climatic fluctuations reflected in the evolution of fluvial systems of central eastern europe 60 8 ka cal bp abstract in general the evolution of fluvial systems in central eastern europe reflects the main phases of climatic changes during the period of 60 8 ka cal bp registered in greenland ice cores and their isotopic 18 o curves the greenland isotope curve shows many more wiggles and stages than the fluvial record of the same time especially during the interpleniglacial phase in central eastern europe we observe several deviations from those climatic trends connected with different factors among which are the long distance of the region from the atlantic ocean and an increase in continentality at times this region was occupied by permafrost although the coexisting warm summers during a part of the studied period enabled the presence of a forest cover these factors together controlled the specific features of the fluvial regime and sediment load reflected in alternating trends to erosion or aggradation and from meandering to braiding the permafrost influenced snowmelt floods and tendency to braiding the dense vegetation with trees reduced the supply of sediments and stabilized the meandering channels very distinct changes occurred in the river valleys that drain the mountains where ceaseless fluctuations of vegetation vertical zones were present especially during the unstable interpleniglacial when the supply of load from the higher vegetation zones was increased this system controlled by the climate and plant vegetation was modified by other factors including tectonics wind activity during dry periods blocking of valleys by ice sheets meltwater supply and sea level fluctuations of two reservoirs

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

biomarker based reconstructions of holocene lake level changes at lake gahai on the northeastern tibetan plateau holocene hydrological changes in regions dominated by the westerlies significantly differ from those by the asian summer monsoon the high elevated northeastern tibetan plateau located in between is likely influenced by the interactions of both circulation systems here we attempt to use biomarkers n alkanes and alkenones to reconstruct holocene lake level changes at lake gahai in the qaidam basin we choose a sediment core drilled at the lake shore where biomarkers would be sensitive to lake level changes the n alkane records show high average chain length acl high carbon preference index cpi and low proportion of aquatic macrophyte paq values at 7 2 kyr thousand calibrated years ago with peaked values around 6 kyr whereas low acl low cpi and high paq values occurred after 2 kyr and before 7 kyr no alkenones were detected at 7 2 kyr suggesting that lake level at this period was incapable of constantly reaching to the coring site therefore combined results provide unambiguous evide

lateglacial early holocene fluvial reactions of the jeetzel river elbe valley northern germany to abrupt climatic and environmental changes abstract mechanisms of climatic control on river system development are still only partially known palaeohydrological investigations from river valleys often lack a precise chronological control of climatic processes and fluvial dynamics which is why their specific forces remain unclear in this multidisciplinary case study from the middle elbe river valley northern germany multiple dating of sites palynostratigraphy radiocarbon and osl dating and high resolution analyses of environmental and climatological proxies pollen plant macro remains and ostracods reveal a continuous record of the environmental and fluvial history from the lateglacial to the early holocene biostratigraphical correlation to northwest european key sites shows that river system development was partially out of phase with the main climatic shifts the transition from a braided to an incised channel system predated the main phase of lateglacial warming 14 6 ka bp and the meandering river did not change its drainage pattern during the cooling of the younger dryas period environmental reconstructions suggest that river dynamics were largely affected by vegetation cover as a vegetation cover consisting of herbs dwarf shrubs and a few larger shrubs seems to have developed before the onset of the main lateglacial warming and pine forests appear to have persisted in the river valley during the younger dryas in addition two phases of high fluvial activity and new channel incision during the middle part of the younger dryas and during the boreal were correlated with changes from dry towards wet climatic conditions as indicated by evident lake level rises lateglacial human occupation in the river valley which is shown by numerous palaeolithic sites forming one of the largest settlement areas of that period known in the european plain is assigned to the specific fluvial and environmental conditions of the early allerod

miocene sedimentary environment and climate change in the northwestern qaidam basin northeastern tibetan plateau facies biomarker and stable isotopic evidences abstract facies biomarker and stable isotopic records from the miocene lacustrine sediments in the northwestern qaidam basin were investigated to reconstruct the miocene sedimentary environment and climatic history three distinct facies can be recognized these include the following 1 gray black laminated mudstone and marlstone which represent a semi deep fresh to semi brackish lake environment 2 gray yellowish massive mudstone marlstone and siltstone and 3 yellowish massive sandstone which imply a shallow brackish lake environment the decreasing c 27 c 31 and c 27 c 29 c 31 c 33 values the increasing acl mean chain length values of n alkanes and the vertical evolution of sedimentary environments indicate the overall intensified aridity which is considered to be an integrated result of high elevation of the himalaya tibetan system retreat of the paratethys and global cooling high fluctuations of the 18 o values and primary dolomite contents reveal the hydrologically closed paleolake with intermittently open conditions in the study area during middle late miocene the qaidam basin is suggested to be hydrologically segmented based on the stable isotopic data comparison between the study area and the northeastern area the most negative end of the oscillations of the 18 o values indicating the minimal evaporation which likely represents the isotopic ratio of the meteoric water surprisingly conveys stability in the shang youshashan and shizigou formations and displays a positive 2 5 shift this significant shift was probably due to the climatic aridification and air mass changes around 10 8 ma rather than the global cooling

a sea change in smuggler s cove detection of decadal scale compositional transitions in the subfossil record abstract molluscan death assemblages in coastal marine settings are compositionally dynamic in time and space here we describe a significant temporal faunal transition recorded over some two decades in the upper sedimentary veneer of a currently accumulating shell bed in smuggler s cove st croix us virgin islands it had been demonstrated previously that molluscan death assemblages in the study area reflect the living assemblages from which they were derived further a gradient among these assemblages reflects an environmental gradient of decreasing seagrass cover and increasing bioturbation transitioning from lucinid bivalves and grazing gastropods inhabiting dense seagrass to other bivalves and predatory gastropods in bioturbated areas more than two decades after initial sampling the study area was resampled to investigate whether the environment and assemblages had changed relative to those reported in the earlier investigation results demonstrate that while the general faunal gradient has remained intact a notable area wide biotic transition occurred among the living molluscan assemblages during the intervening period and is reflected in the accumulated death assemblage this change is characterized by a major decline in the previously prolific grazing gastropod cerithium litteratum and a similarly dramatic increase in the abundance of another grazing gastropod eulithidium affine while the cause of this transition is not yet known it demonstrates the compositional dynamism of this time averaged assemblage on a decadal time scale

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

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

fluvial history of the sub carpathian basins poland during the last cold stage 60 8 cal ka bp abstract the fluvial landforms of the last cold stage are represented in the sub carpathian basins by a system of 2 3 terraces which grade into alluvial fans of a height of 15 20 8 12 and 6 8 m above the present riverbeds in the mountain foreland in the vistula river valley the 15 20 m high terrace covered with loess extends along the western margin of the sandomierz basin and northern margin of the carpathians away from the mountain margin it passes into the sandy terrace plain with dunes it is formed of at least two interpleniglacial alluvial fills the older one dated at 48 36 ka bp over 50 40 6 ka cal bp and the younger one dated 30 25 ka bp 34 1 29 0 ka cal bp thus pertaining to the upper pleniglacial this latter forms a terrace 15 m high in general accumulation of fluvial sediments interrupted with erosion phases dominated in the mountain foreland during the period 60 25 ka bp over 60 29 ka cal bp the most significant erosion phase took place before the maximum extension of the vistulian weichselian wisconsinian ice sheet i e before 25 20 ka bp 29 24 ka cal bp and was connected with a change from an oceanic to a more continental climate the next alluvial fill of terrace 8 12 m high with remnants of braided river channels was formed at the end of the upper plenivistulian the incision of the river channels below the present channel level was followed by aggradation in the late vistulian 15 13 ka bp 18 2 15 6 ka cal bp accompanied by a change in river channel system from braided to meandering in the wisloka and san river valleys alluvial plains extending by lateral erosion of large meanders were abandoned by rivers mainly in the younger dryas and the preboreal the late vistulian large palaeomeanders are missing along lower sola and lower dunajec these rivers fed from higher mountains had still tendency to braiding the climate cooling of the younger dryas brought an increase in the delivery of bedload to the river channels and a tendency to braiding in vistula valley drwinka depression the expansion of forest in the early holocene reduced the water discharge and the size of meanders as a result their width fallen by 3 5 times alluvial data showed also a distinct humid climatic phase ca 9 5 8 5 ka cal bp

molecular fossils in a pleistocene river terrace in southern china related to paleoclimate variation abstract the red paleosols oxisols in southern china provide a record of global climate oscillation during at least the last 0 80 ma here we present a correlation between the marine oxygen isotope record stage 11 21 and the paleosol molecular fossil signature in the fourth xiushui river terrace in southern china temporal variations seen in two molecular ratios c15 21 c22 33n alkanes and pristane to phytane pr ph down the paleosol profile are postulated to have arisen from variations in biological input and subsequent pedogenesis in response to the changing strength of the east asian summer monsoon climate the preliminary findings suggest strong couplings among the soil vegetation and climate and provide a basis for a correlation between the terrestrial and oceanic records

the use of faunal gradient analysis for intraregional correlation and assessment of changes in sea floor topography in the type cincinnatian abstract in paleobiology and stratigraphy there is a growing need to develop high resolution chronostratigraphic frameworks at regional scales which would permit unprecedented assessments of spatiotemporal variation in preserved biotas here we present an intraregional correlation for the kope and lower fairview formations of the type cincinnatian on the basis of detrended correspondence analysis dca of faunal census data we believe that the method also holds promise as a tool of correlation in other fossiliferous venues the data were collected directly in the field at closely spaced stratigraphic intervals but with relatively coarse taxonomic and quantitative data resolution this approach is independent of lithologic assessments and does not require the delineation of sequence stratigraphic architecture in the study area faunal curves were constructed for each locality on the basis of stratigraphic changes in sample scores for dca axis 1 the curves were smoothed to reveal a long term signal of

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

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

a north to south transect of holocene southeast atlantic continental margin sediments relationship between aerosol transport and compound specific δ13c land plant biomarker and pollen records 1 we examined near surface late holocene deep sea sediments at nine sites on a north south transect from the congo fan 4 s to the cape basin 30 s along the southwest african continental margin contents distribution patterns and molecular stable carbon isotope signatures of long chain n alkanes c27 c33 and n alkanols c22 c32 are indicators of land plant vegetation of different biosynthetic types which can be correlated with concentrations and distributions of pollen taxa in the same sediments calculated clusters of wind trajectories and satellite aerosol index imagery afford information on the source areas for the lipids and pollen on land and their transport pathways to the ocean sites this multidisciplinary approach on an almost continental scale provides clear evidence of latitudinal differences in lipid and pollen composition paralleling the major phytogeographic zonations on the adjacent continent dust and smoke aerosols are mainly derived from the western and central south african hinterland dominated by deserts semi deserts and savannah regions rich in c4 and cam plants the northern sites congo fan area and northern angola basin which get most of their terrestrial material from the congo basin and the angolan highlands may also receive some material from the chad region very little aerosol from the african continent is transported to the most southerly sites in the cape basin as can be expected from the present position of the phytogeographic zones the carbon isotopic signatures of the n alkanes and n alkanols both become isotopically more enriched in 13c from north to south the results of the study suggest that this combination of pollen data and compound specific isotope geochemical proxies can be effectively applied in the reconstruction of past continental phytogeographic developments

high dead live mismatch in richness of molluscan assemblages from carbonate tidal flats in the persian arabian gulf live dead ld fidelity studies are a fundamental tool for assessing the quality of the paleobiological information preserved in the fossil record an important feature of death assemblages das is that they are time averaged to some degree previous studies found that subtidal carbonate environments are characterized by lower time averaging in comparison to siliciclastic settings primarily because of a high rate of shell loss due to bioerosion and dissolution these factors lead to increased temporal resolution in subtidal carbonate death assemblages das but more intense bias in species composition due to differential loss of vulnerable shells a consequence of lower time averaging is a better match in live dead ld richness we evaluated ld fidelity of molluscan assemblages from soft sediments in subtropical carbonate tidal flats along the coast of the united arab emirates persian arabian gulf to test these predictions a total of 7193 mollusks from six sites were analyzed we found that das are on average over five times richer than living assemblages las at site scale and nearly five times at habitat scale we found that early cementation lateral mixing intense bioturbation and moderate sedimentation rates can account for large ld differences in richness differential intensity in lateral mixing by post mortem transport inflated alpha beta and gamma diversity by 28 10 and 42 however beta diversity is strongly underestimated in das when compared to las evenness was larger in das both at site and at habitat scales but there was only a high mismatch at sites with patchy las fidelity of feeding guild structure was high for rank abundance with secondary consumers well represented in das the occurrence of out of habitat taxa did not affect fidelity in rank abundance of feeding guild structure our results suggest that time averaging in carbonate tidal flats can potentially be higher compared with subtidal carbonate environments

paleoclimate changes of the last 1000 yr on the eastern qinghai tibetan plateau recorded by elemental isotopic and molecular organic matter proxies in sediment from glacial lake ximencuo abstract total organic carbon corg and nitrogen ntot concentrations and isotope compositions and n alkane and n alkan ol molecular biomarker compositions were measured in two parallel sediment cores from lake ximencuo a typical glacial lake on the eastern qinghai tibetan plateau qtp to reconstruct local climatic variations during the past 1000 yr concentrations of corg and ntot vary similarly with changes in precipitation recorded by tree rings in dulan northeastern qtp indicating their close relation to precipitation carbon preference index cpi values of c22 c33 n alkanes and c22 c28 n alkan 1 ols and average chain length acl values of c27 c33 n alkanes generally negatively correlate with 13corg and 15ntot and also vary comparably with the oxygen isotope temperature record from the dunde ice core northeastern qtp these patterns indicate that high cpi values and negative shifts of the 13corg and 15ntot correspond to warmer conditions that favor the growth of vascular land plants and that lower values and positive shifts correspond to cooler conditions in the lake ximencuo locality this observation contradicts previous interpretations from peat and modern soil studies that conclude that the cpi indices were controlled by microbial degradation under different climate conditions here we propose that the changes of organic matter sources under different climate regimes combined with physiological adjustments of vascular plants to different air temperatures might yield different cpi responses to climate changes in glacial plateau lakes air temperature and precipitation increases and decreases reconstructed in this 1000 yr study were generally independent of each other but they both occurred at centennial or multi centennial scales the interaction between subtropical asian monsoon and mid latitude westerly atmospheric circulation systems probably dominated the local precipitation variations in the lake ximencuo catchment whereas solar insolation volcanism and greenhouse gas variations were likely responsible for the air temperature changes that are recorded in the lake sediments and that are consistent with regional temperature variations in the eastern qtp

climate related river activity at the weichselian holocene transition a comparative study of the warta and maas rivers huvial systems from the dutch and polish lowlands are compared for their evolution during the weichselian deglaciation period in both regions the pleniglacial braided river pattern changed to a meandering pattern in the beginning of the lateglacial several transitional stages between braided and high sinuosity meandering systems have been recognized a difference in fluvial activity is found during the younger dryas when the maas transformed to a braided pattern while the warta maintained its meandering pattern phases of erosion and aggradation are more or less synchronous in the different river basins but their intensity may differ greatly the major characteristics of the fluvial systems are obviously a response to the general climatic evolution and related to changes in vegetation the regional differences are of minor importance and can be explained by site specific factors threshold values within the latter factors define the changes in river dynamics

molecular isotopic stratigraphy of long chain n alkanes in lake baikal holocene and glacial age sediments the molecular distribution and the carbon isotopic composition d 13 c of n alkanes extracted from a lake baikal core spanning the last 20 kyr of sediment accumulation have been investigated a terrestrial origin has been inferred for the odd carbon numbered long chain c27 n alkanes on the basis of the observed high cpi27 33 values range 8 7 10 8 typical of n alkanes derived from leaf waxes of higher plants a shift in the abundance of n c27 alkane relative to n c31 homologue is observed across the late pleistocene glacial holocene interglacial climate change perhaps indicative of the climate induced vegetational change previously deduced from palynological analyses compound specific isotope analyses indicate remarkably uniform d 13 c values in the range of 31 0 to 33 5 for the leaf wax c27 c33 nalkanes in the entire cored sequence such an isotopic compositional range is characteristic for n alkanes biosynthesized by plants utilizing the c3 photosynthetic pathway our data suggest that the observed 13 c enrichment in the bulk organic matter in the glacial age sediments relative to d 13 c values of total organic carbon in the holocene section is therefore unlikely to be attributed to an expansion of c4 type vegetation in the baikal watershed during the late pleistocene glacial interval 2000 elsevier science ltd all rights reserved

last glacial interglacial cycle in the evolution of river valleys in southern and central poland abstract the last glacial interglacial cycle is represented usually by several cuts and fills which have formed 2 3 terrace steps from the last cold stage and by two or more fills of lateglacial holocene age their number depends on the size of the river valley and the position in the longitudinal profile the sequence of changes reflects shorter stadial interstadial climatic fluctuations generally aggradation dominates during the cooler phases of the vistulian and during the interpleniglacial the most distinct erosional phases occurred during the change from a more oceanic to a more continental climate before the maximum extension of the ice sheet 25 20 ka bp and during the upper pleniglacial lateglacial transition 15 13 ka bp the second phase coincides with the rapid downcutting in the lower course of the main vistula valley which had been blocked earlier by the scandinavian ice sheet in the holocene aggradation prevailed accelerated by anthropogenic soil erosion it was only in the mountain foreland that shorter lived hydrological changes resulted in well expressed several cuts and fills

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

climatic and environmental changes reflected by lake level fluctuations at gerzensee from 14 850 to 13 050yrbp abstract high resolution sediment analysis at gerzensee swiss plateau focused on the reconstruction of lake level changes during the last glaciation greenland stadial 2a gs 2a and a large portion of lateglacial including the gerzensee oscillation the chronology is derived from a comparison of the oxygen isotope stratigraphy established at gerzensee with that of the ngrip ice core on a multi millennial scale differences between the lake level and oxygen isotope records established from cores gej gek reflect a complex interplay among climate vegetation and lake level during retreat of the ice sheet but on a multi centennial scale both the lake level and oxygen isotope records show a general agreement i e cool periods such as greenland stadial gs 2a and greenland interstadials 1d and 1b which coincided with more positive water budgets and conversely warm periods greenland interstadials 1e and 1c with more negative water budget this is in agreement with the regional pattern of palaeohydrological changes reconstructed from previous studies despite possible reduced annual precipitation during gs 2a the maintenance of relatively high lake level conditions at gerzensee at this time could have resulted from reduced evaporation and stronger runoff on bare slopes whereas during the lateglacial interstadial the phases of lake level lowering may have been associated with summer dryness linked to increasing summer insolation

dead delta s former productivity two trillion shells at the mouth of the colorado river the diversion of the colorado river by dams and irrigation projects started in the 1930s triggered the collapse of the colorado delta ecosystem paleontological ecological geochronological stable isotope field and satellite image data provide estimates of the delta s benthic productivity during the 1 k y directly preceding the artificial shutdown of the river at least 2 1012 shells of bivalve mollusks make up the current beaches and islands of the delta the 125 individual valves dated using 14c calibrated amino acid racemization indicate that these shells range in age from a d 950 to 1950 seasonal intrashell cycles in 180 values indicate that average sized bivalves lived at least 3 yr the most conservative calculation based on these numbers indicates that during the time of natural river flow an average standing population of 6 109 bivalve mollusks population density 50 m2 thrived on the delta in contrast the present abundance of shelly benthic macroinvertebrates is 94 lower 3 m2 in 1999 2000 the dramatic decrease in abundance testifies to the severe loss of benthic productivity resulting from diversion of the river s flow and the inadequacy of its partial resumption 1981 to present an integration of paleontological records with geomorphological geochemical and geochronological data can provide quantitative insights into human impact on coastal ecosystems

organic geochemical characteristics and organic matter enrichment of mudstones in an eocene saline lake qianjiang depression hubei province china abstract the qianjiang depression is a typical eocene hypersaline lake basin developing good source rocks in the qianjiang formation which have recently been identified as a potential target for saline lacustrine shale oil exploration previous studies have only focused on estimates of source rock potential and reservoir quality however studies on organic matter enrichment mechanisms in evaporative environments are limited based on organic geochemical and mineralogical data as well as sedimentological analyses we researched the factors controlling differences in organic matter enrichment in the basin the results show that total organic carbon toc contents are closely associated with lithofacies with distinct variations three main lithofacies associations las were identified 1 glauberite rich la1 with medium toc 2 carbonate rich la2 with high toc and 3 anhydrite rich la3 with low toc the distribution of biomarkers from 14 samples indicate both higher land plants and aquatic organisms were involved in the organic matter accumulations combining experimental results on gammacerane c30 hopane extended tricyclic terpane ratio etr sr ba v ni and sedimentary characteristics we analyzed the sedimentary environments of the three las la1 was deposited in a salinity stratified waterbody with strong evaporation la2 was deposited in a still stratified deep waterbody whereas la3 was deposited in a disturbed saline waterbody sedimentary environments not only controlled the formation of the lithofacies but also influenced the organic matter sources and preservation relatively low salinity strong anoxic condition without physical disturbance appropriate nutritional terrigenous material inputs and algal blooms produced the best organic matter enrichment in the saline lake system

response of the selle river to climatic modifications during the lateglacial and early holocene somme basin northern france abstract research on lateglacial sequences from the selle valley leads to an overview of its evolution in relation to climatic variations between the end of the weichselian upper pleniglacial and the beginning of the holocene the first major modification of the fluvial morphology is dated at the upper pleniglacial lateglacial transition 13 000 14 c yr bp at that time the response to climatic improvement and environmental modifications is marked by downcutting and evolution from a braided river to a transitional river pattern bolling infilling in the newly created channels after a short cold phase recorded in a thin calcareous bed at the top of the bolling peat attributed to the older dryas dr ii the allerod is characterized by the deposition of organic overbank silts within a large single channel meandering system in lower slope environments this period is also marked by slow rates of colluvial accumulation and by the development of upbuilding soils allerod soil on the other hand the end of the lateglacial is characterised by the infilling of the whole valley by fine calcareous overbank silts during the younger dryas cold phase overflow of a large single channel and lateral input of chalk mud a second major downcutting phase occurs at the beginning of the holocene at around 10 000 bp in parallel with another rapid climatic improvement and the renewed spread of vegetation from a general point of view the evolution of fluvial environments in the selle valley is comparable with many other river valleys in nw europe showing that fluvial systems react very quickly to climatic variations of short duration 1000 to 100 years finally in the upper selle river incision events occur clearly before the main modifications of the vegetal cover they are most likely linked to a rapid shift in the balance between water discharge and sediment supply caused by climate modifications shift to more temperate and oceanic conditions and the resulting environmental changes cessation in aeolian sedimentation strong reduction of slope processes permafrost disappearance and soil development

estuarine fluvial floodplain formation in the holocene lower tagus valley central portugal and implications for quaternary fluvial system evolution abstract we present a brief synthesis of the quaternary fluvial record in the lower tagus basin central portugal concentrating on factors controlling infill and incision the holocene part of the record forms the focus of this paper and guides the questioning of the basic assumptions of the established quaternary fluvial evolution model in particular the link between sea level change and fluvial incision deposition we suggest that several incision aggradation phases may have occurred during glacial periods major aggradation events may overlap with cold episodes while incision appears to concentrate on the warming limb of climate transitions the complex stratigraphy of the quaternary record in the lower tagus valley is influenced by repeated base level and climate changes this paper submits the first chronostratigraphic framework for valley fill deposits in the lower tagus area sea level rise forced aggradation and controlled deposition of the fine grained sedimentary wedge underlying the low gradient lower tagus floodplain investigations have focused on the lower muge tributary where rapidly aggrading estuarine and fluvial environments were abruptly established 8150 cal bp as sea level rose base level at the valley mouth controlled the upstream extent of the fine grained backfill tidal environments disappeared abruptly 5800 cal bp when the open estuary at the muge confluence was infilled by the tagus river the decrease and final still stand of sea level rise led to floodplain stabilisation with peat 6400 5200 cal bp and soil formation 5200 2200 cal bp localised renewed sedimentation 2200 200 cal bp is linked to human activity

stratigraphic paleoecology bathymetric signatures and sequence overprint of mollusk associations from upper quaternary sequences of the po plain italy upper quaternary sequences of the po plain italy were used to assess the informative strength and sequence stratigraphic overprint of quantitative paleoecological patterns three densely sampled cores 89 samples 98 genera 23 280 specimens dominated by extant mollusk species with known environmental distributions were analyzed with detrended correspondence analysis dca the dca scores calibrated using extant genera provided outstanding estimates of bathymetry 3 m and related environmental parameters depth related successions of mollusk associations delineated by using dca were consistent with independent sequence stratigraphic interpretations and yielded insights inaccessible via routine techniques e g depth estimates for maximum flooding surfaces the dca ordination demonstrates the severity of the sequence stratigraphic overprint samples are highly uniform taxonomically during late transgressive systems tracts and highly variable during the following highstand systems tracts when analyzed across comparable systems tracts similar species associations repeat during the last and current interglacial cycles suggesting that po plain mollusk associations have remained remarkably stable over the past 125 k y the results are consistent with the bathymetric interpretation of the dc axis 1 postulated previously for the paleozoic fossil record demonstrate the sequence stratigraphic overprint of paleoecological patterns predicted by computer modeling and illustrate the utility of quantitative paleoecological patterns in augmenting sequence stratigraphic interpretations

sensitivity of weichselian fluvial systems to climate change nochten mine eastern germany abstract this paper aims to contribute to the understanding of fluvial system response to climate change during the last glacial interglacial cycle fluvial and aeolian successions have been studied in the opencast brown coal mine nochten in eastern germany an absolute chronology was established by luminescence and 14 c dating enabling to demonstrate the relations between depositional units and changes in sedimentary environment over time with regional climatic and vegetational changes it is concluded that the major climatic periods coinciding with the oxygen isotope stages are generally reflected in the fluvial sequence by distinct fluvial environments major climatic changes oxygen isotope stage boundaries have been preserved in the fluvial record as erosional bounding surfaces and by changes in fluvial style rapid climate changes like the middle pleniglacial dansgaard oeschger cycles are in general not reflected in the fluvial succession these cycles were too short or with too low amplitude to cause a strong vegetational response and related changes in water and sediment supply it is emphasized that also the preservation potential of short lived climatic warming events in high energy fluvial systems is low warming events may however have been preserved in lacustrine successions in former thermokarst lakes a strong cooling event at ca 40 ka leading to continuous permafrost conditions and changes in the water and sediment budget was reflected in the fluvial archive by a change from sandy anabranching to braided river conditions

distribution of the c37 tetra unsaturated alkenone in lake qinghai china a potential lake salinity indicator abstract the alkenone unsaturation index u k 37 has been applied to reconstruct past temperature changes in both marine and lacustrine systems however few studies have addressed whether the relative abundance of the c 37 4 alkenone to the total c 37 production c 37 4 can reflect surface salinity changes in lacustrine systems here we present long chain c 37 alkenone distribution patterns in surface sediments from lake qinghai china surface sediments were sampled over a large range of surface salinity changes 1 7 25 g l within lake qinghai and its surrounding lakes while temperature differences at these sampling locations should be relatively small we have found that c 37 4 varies from 15 to 49 as surface salinity decreases we tentatively describe this c 37 4 salinity link with a general linear regression c 37 4 53 4 7 8 1 73 0 45 s n 28 r 2 0 62 although step wise c 37 4 changes in response to salinity variation may exist u k 37 values vary between 0 10 and 0 16 at these sites and the inferred range of lake water temperature changes is 2 3 c suggesting that u k 37 largely reflects temperature signal across a large salinity range consistent with previous findings that u k 37 can indicate temperature changes over a large diversity of environmental settings we have also found that u k 37 values are correlated with salinity changes r 2 0 4 and thus cannot exclude potential temperature effect on c 37 4 and salinity effect on u k 37 in this study however even extreme estimates of temperature differences within the lake are still unable to explain the observed c 37 4 changes we therefore suggest that c 37 4 could be used to infer past lake salinity changes at a regional scale

characterisation of n alkanes and their hydrogen isotopic composition in sediments from lake qinghai china the distributions of n alkanes and their hydrogen isotopic composition dd in surface and core sediments from the saline qinghai lake were measured to assess whether or not biological source information was recorded in the dd values of n alkanes the results indicate that the n alkane distributions between shallow water surface and core sediments were similar and closer to those of terrestrial herbaceous plants from the qinghai lake surrounding areas rather than the aquatic plants living in the lake the n alkanes in the surface and core sediments had similar mean dd values ranging from 185 to 133 and 163 to 142 respectively the mean dd values of n alkanes in the sediments showed that the even n alkanes were heavier in d compared with the odd homologues

environmental controls on shallow subtidal molluscan death assemblages on san salvador island the bahamas abstract ecological studies that span multiple marine depositional environments frequently find that benthic invertebrate assemblages are correlated primarily with an onshore offshore gradient variability within the same depositional environment is inferred to not result from water depth differences but other parameters such as substrate consistency and shear stress modern studies focusing on assemblage variations within the same depositional environment can identify which variables affecting assemblage compositions are independent of water depth this study examines the environmental controls on the composition of molluscan death assemblages from the shallow subtidal environments of san salvador island molluscan assemblages were tabulated from twenty nine bulk samples collected from four locations around san salvador island representing seagrass meadows open sandflats and patch reef systems common in the shallow subtidal in addition quantitative environmental data for each sample was characterized including seagrass density water depth temperature ph dissolved oxygen and grain size as well as qualitative observations of wave energy and bioturbation cluster analysis and canonical correspondence analysis cca were performed to identify environmental gradients associated with molluscan assemblage composition cluster analysis and cca axis 1 identify seagrass coverage and substrate consistency as the primary environmental variables describing molluscan death assemblage compositions cca axis 2 identifies wave energy bioturbation and dissolved oxygen as the secondary environmental variables though the small range of dissolved oxygen values 17 21 mg l collected using single instantaneous measurements make it unclear whether the oxygen gradient is ecologically significant for our time averaged assemblages our analysis demonstrates the variability of assemblages within a single depositional environment as well as the utility of fine resolution studies for identifying secondary environmental variables that control the composition of marine invertebrate assemblages

total organic carbon isotopes a novel proxy of lake level from lake qinghai in the qinghai tibet plateau china abstract the isotopic compositions of total organic carbon toc in lakes have been widely used to interpret paleoclimatic changes and the depositional environments of lake sediments however the main factors that affect the carbon isotopes of toc source of organic material water condition and others may vary in different lake sediment records which have limited the applicability of organic carbon isotopes in explaining biogeochemical and environmental changes in lakes in this study the organic carbon isotopic compositions of aquatic plants and surface sediments from lake qinghai and the living terrestrial plants and surface soils around the lake were systematically investigated to identify the sources of toc in the sediments and the significance of the organic carbon isotopes of sedimentary toc we found that the aquatic plants in the deep water areas 10 m were primarily dominated by cladophora but submerged plants potamogeton and ruppia l are the dominant species in shallow water 13 c org values 33 6 to 28 6 that are caused by c 3 like photosynthesis but the submerged plants have enriched 13 c org values 17 8 to 15 4 that are caused by c 4 like photosynthesis in addition the 13 c org values of cladophora become more negative with increasing water depth because of the slow photosynthetic rate caused by the weak light intensity at depth the isotopic data indicate that the carbon isotopes of organic material in the surface sediments are primarily controlled by the types of aquatic plant and that the 13 c org values of toc can be used to indicate the variation of the water depth lake level the organic carbon isotopic data from the 1f core showed that the water was shallow

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

modeling the response of the rhine meuse fluvial system to late pleistocene climate change abstract we use a landscape evolution model to infer the effect of late pleistocene climate change on the incision aggradation behaviour of the rhine meuse fluvial system we model the routing of runoff and sediment in the catchment in order to predict grainsize trends and the incision and aggradation behaviour in the downstream reach where we compare it to the sequence of events and grainsize characteristics inferred from borehole corings this sequence starts with an important incision taking place around the mis 3 to mis 2 climatic transition during the coldest part of mis 2 a coarse grained sedimentary unit is deposited that shows an upward increase in the sand gravel ratio the model experiments do not predict an incision at the mis 3 to mis 2 transition therefore the incision should be attributed to other causes most likely effects of glacio isostatic uplift however a relative upward increase in sand content of the sediments is predicted by the model this increase is the result of the difference in transport rates between sand and gravel starting from a homogeneous pre existing mis 3 deposit the gravel content in the active layer increases because the sand is removed quickly and transported further downstream whereas the gravel travels slowly and piles up with gravel originating from immediately upstream resulting in a net accumulation at a later stage sand originating from much further upstream progrades fan like over the gravelly deposits according to the record during the early late glacial warming part of mis 2 bolling allerod interstadial neither incision nor aggradation has taken place this is in accordance with modelling results which show that despite the reduction of sediment input due to re vegetation of hillslopes sufficient sediment remains available for fluvial transport in the channel network itself it takes several thousands of years before effects of sediment depletion in the catchment are noted downstream that is why we argue that the inferred incision at the late late glacial the start of the younger dryas in our downstream study area might reflect depletion effects related to the preceding early late glacial conditions in general our modelling results show that terraces along one large fluvial system are diachronic features in particular terrace surfaces are older upstream compared to downstream in addition complex responses to climate change are likely to occur in a large fluvial system like the rhine meuse and correlation of morphological features in the fluvial record to specific short term palaeo climatic events for example dansgaard oeschger events could be risky without consideration of catchment size characteristics and associated response times

dust induced changes in phytoplankton composition in the tasman sea during the last four glacial cycles 1 an increase in iron supply associated with enhanced dust inputs could be responsible for higher marine phytoplankton production leading to the typically lower glacial atmospheric co2 concentrations as suggested by the iron hypothesis the enhanced dust supply may also have provided the oceans with significant amounts of silica which would have favored the growth of diatoms over coccolithophores as suggested by the silica hypothesis here we present new data on molecular biomarkers in a sediment core from the midlatitudes of the southern hemisphere which reveal dust induced changes in the relative contribution of the phytoplankton to total productivity our results illustrate a shift in the relative abundance of siliceous over calcareous organisms during glacial times when terrestrial aeolian input was enhanced although we did not detect a significant glacial decrease in coccolithophorid productivity the decrease in the caco3 corg rain ratio could have still contributed to some extent in lowering atmospheric co2 levels

saturated hydrocarbons in the sediments of lake apopka florida lake apopka sediments were analyzed for n alkanes and total organic carbon toc from which long chain hydrocarbon short chain hydrocarbon ratios lhc shc and lhc toc and shc toc ratios were calculated these ratios were used to distinguish the three types of organic sediments that originated historically mainly from byproducts of the primary producer community these types are phytoplankton derived sediments deposited during the hypereutrophic phase of the lake macrophyte derived sediments deposited during a low nutrient clear water phase and transitional sediments deposited as the primary producer community shifted rapidly in the late 1940s from macrophyte dominance to phytoplankton abundance the three ratios employed distinguish the three sediment types with exceptions that may result from a mixture of sediment types formed during the transition from macrophyte abundance to phytoplankton abundance this study supports the hypothesis that the rapid shift from macrophyte dominance to phytoplankton dominance was induced by anthropogenic phosphorus loading more detailed sampling and n alkane analysis of cores from lake apopka have the potential to define when changes in the primary producer community occurred and to infer the temporal dynamics of the well known shift in the primary producer community

paleosalinity in a brackish lake during the holocene based on stable oxygen and carbon isotopes of shell carbonate in nakaumi lagoon southwest japan abstract based on the relationship between salinity and 18 o and 13 c of modern shells in the lake nakaumi shinji lagoon system southwestern japan where the salinity changes regularly from ca 1 psu to 34 psu a paleosalinity record for nakaumi lagoon during the holocene has been derived from bulk mollusk shell 18 o and 13 c data the robust relationships between the salinity and modern shell 18 o ar and 13 c ar aragonite were used to calibrate the paleosalinity reconstruction the salinity relationships are expressed by the regressions salinity psu 3 86 18 o ar vpdb 33 9 n 18 r 0 978 salinity psu 4 05 13 c ar vpdb 31 8 n 18 r 0 977 applying these equations to bulk shell 18 o ar and 13 c ar in the 20 m sediment core very similar salinity histories were reconstructed from either oxygen or carbon isotope ratio data at the beginning of lacustrine sediment deposition 8000 7500 14 c yr b p paleosalinity of the bottom water in the central portion of nakaumi lagoon increased from 22 to 32 psu during the 7500 5500 yr b p interval which approximately corresponds to the holocene climatic optimum and high sea level stand salinity ranged from 27 to 37 psu after 5500 yr b p salinity lessened under the cooling climate with a minimum value of 24 27 psu at 3000 1000 yr b p the results show a consistent relationship between climate change sea level and salinity in the lagoon during the holocene

two late pleistocene climate driven incision aggradation rhythms in the middle dnieper river basin west central russian plain abstract in valleys of the river seim and its tributaries in the middle dnieper basin west central russian plain two low terraces t1 10 16 m and t0 5 7 m above the river and a floodplain 2 4 m with characteristic large and small palaeochannels exist a range of field and laboratory techniques was applied and 30 new numerical ages osl and 14c dates were obtained to establish a chronology of incision and aggradation events that resulted in the current valley morphology two full incision aggradation rhythms and one additional aggradation phase from the previous rhythm were recognized in the late pleistocene holocene climate cycle the following events were detected 1 late mis 5 early mis 4 aggradation of terrace t1 following the deep incision at the end of mis 6 2 late mis 4 40 30 ka incision into terrace t1 below the present day river formation of the main scarp in the bottom of the valley between terrace t1 and terrace t0 floodplain levels 3 mis 2 aggradation of terrace t0 lateral migrations of a shallow braided channel located few meters above the present day river since 25 ka through the lgm 4 18 13 ka incision into terrace t0 below the modern river multiple thread channels concentrated in a single flow that at some places formed large meanders in the period 15 13 ka high floods that rose above the present day floods left large levees and overbank loams on terrace t0 5 younger dryas holocene transition aggradation up to the modern channel level transformation of large late glacial to small holocene meanders the established incision aggradation rhythms are believed to be manifested over the central russian plain outside the influence of ice sheets in the north and base level changes in the south the two phase deepening of the valley occurred in the last quarter of the last glacial epoch but can not be attributed directly to the glacial interglacial transition both the detected incision events correspond to relatively warm climate phases late mis 3 post lgm warming including the bolling allerod interstadial anomalously large size of the preserved river palaeochannels prove that the post lgm incision phase was induced by a climatically forced large increase of water runoff considerable increase of water discharges is considered the most probably cause for the late mis 4 incision phase also therefore river incision seems to have been governed rather by changing water runoff that oscillated in phase shift with the thermal regime

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

molluscan live dead agreement in anthropogenically stressed seagrass habitats siliciclastic versus carbonate environments abstract molluscan live dead fidelity studies investigate the influences of anthropogenic activities on marine ecosystems by comparing the taxonomic composition of a living community to its corresponding death assemblage environments subjected to intense anthropogenic stresses tend to yield low fidelity high discordance in rank order abundance and taxonomic similarity between living and dead assemblages this project assesses the sensitivity of the live dead approach by applying various fidelity metrics community richness delta s evenness delta pie rank order correlation spearman rho and taxonomic similarity jaccard chao to molluscan assemblages in seagrass habitats exposed to anthropogenic stresses in different sedimentary environments our study sites include siliciclastic sites in north carolina carbonate sites in florida bay and a siliciclastic carbonate transition locality along the coast of southern florida the dominant forms of human stresses at these seagrass sites consist of increased freshwater runoff increased nutrient runoff and physical substrate disturbance by dredging north carolina and propeller scarring florida bay as a result of such anthropogenic stresses we expected to find low live dead fidelity results at all of our study sites we also anticipated variations in the results between sedimentary environments reflecting intrinsic differences in how molluscan material accumulates and is preserved in siliciclastic versus carbonate settings using bulk sediment samples fidelity analyses consistently yield greater live dead disagreement at the siliciclastic sites despite well documented historical human stresses to florida bay and sediment cores indicating multiple ecological shifts in response to human impacts over time results from carbonate localities yield higher fidelity and provide little evidence for ecological change we argue that greater time averaging allows for the death assemblages at the siliciclastic sites to retain a longer memory of the local communities thus preserving evidence of local ecological changes in contrast less time averaging and more rapid live dead equilibration in carbonate sediments reduces the signal of community changes thus we propose that the live dead fidelity approach is more sensitive at detecting recent ecological changes in siliciclastic versus carbonate environments confirming the conservative nature of the approach and demonstrating the role of taphonomic bias in live dead methodology

fluvial response to weichselian climate changes in the niederlausitz germany the last glacial shows large variations in climate which are reflected in the fluvial record in the niederlausitz eastern germany the entire sequence resembles the fluvial development in other river basins in northwestern europe which show contemporaneous changes in depositional style at the onset of a climatic change during the middle and the late pleniglacial permafrost conditions resulted in an episodic river discharge the presence or absence of vegetation in combination with such ephemeral stream conditions determined the type of river during each period a relatively well developed vegetation cover on the flood plains during the middle pleniglacial resulted in a low sediment yield in combination with the intermittent discharge this caused the development of an ephemeral anastomosing river system a river with stable channels and extensive sandy overbank areas the decline in vegetation cover at ca 28 ka bp caused an increase in sediment yield and peak discharges which resulted in the development of a sandy braided river in adjustment to these new conditions following the coldest period at around 20 ka precipitation was so low that fluvial activity was limited and aeolian deposition took place in the valley 1997 by john wiley sons ltd

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

a global merged land air sea surface temperature reconstruction based on historical observations 1880 1997 abstract a merged land air sea surface temperature reconstruction analysis is developed for monthly anomalies the reconstruction is global and spatially complete reconstructed anomalies damp toward zero in regions with insufficient sampling error estimates account for the damping associated with sparse sampling and also for bias uncertainty in both the land and sea observations averages of the reconstruction are similar to simple averages of the unanalyzed data for most of the analysis period for the nineteenth century when sampling is most sparse and the error estimates are largest the differences between the averaged reconstruction and the simple averages are largest sampling is always sparse poleward of 60 latitude and historic reconstructions for the polar regions should be used with caution

fluvial response to rapid climate change during the devensian weichselian lateglacial in the river great ouse southern england uk few lateglacial 15 200 11 500 cal bp fluvial deposits are known from southern england uk this paper outlines a sedimentological investigation of a lateglacial site near the village of roxton in the middle reach of the river great ouse below the holocene argillaceous alluvium several large gravelly lithofacies units representing long term fluvial processes are recognised based on their lower bounding surfaces and sedimentary features in line with palaeontological evidence and radiocarbon dating detailed facies analysis indicates that the river changed from a braided to a wandering meandering regime in response to the warming induced reduction in nival peak discharge and increase in vegetation cover consisting of birch woodland and grassland during the lateglacial interstadial 15 200 12 700 cal bp this was followed by a change back to a braided river in response to climatic deterioration during the younger dryas chronozone 12 700 11 500 cal bp the interstadial floodplain consisted of both overbank fines and channel lateral or point bar sands and gravels the two suites of contemporaneous sediments in the geological succession may be easily mis interpreted as independent climato stratigraphical units due to their cross cutting relationship and marked difference in facies assemblage lateral channel movement in such a system also implied that the floodplain underwent constant erosion resulting in underdeveloped overbank sequences insufficient to withstand post depositional removal by erosion this probably accounts for the rare preservation of fine textured overbank deposits of the lateglacial interstadial in southern england

timescales climate and river development abstract in the long term glacial interglacial sequences river development follows general climatic evolution however at the scale of one cold warm cycle it appears that the geomorphological effect of river activity is best expressed at times of climatic change such periods of pronounced fluvial action last only a short time in more detail the internal evolution in a drainage basin after a climatic event results in a delayed response of the morphology and sedimentation pattern finally on the shortest timescale local thresholds may play a decisive role in the reactions of river systems it is concluded that the relation between fluvial development and climate is not a simple one but is fundamentally dependant on the timescale