aliphatic hydrocarbons and triterpenes of the congo deep sea fan abstract hydrocarbons were analyzed in sediments from the congo river deep sea fan from the congo river and in sinking particles collected by sediment traps 40 m above the sediment studied sites encompassed three lobes of decreasing age of formation along the canyon sites a f and c and a another lobe system disconnected from the active channel since 4 ka site e terrestrial long chain odd n alkanes were dominant in all sediments of the lobe system unsaturated terpenoids sourced by higher plants such as gammacerene lupene ursene and oleanene were also detected at site c characterized by high accumulation rates 10 20 cm yr 1 the organic matter spends less time in the oxic layer than at other sites and high phytadiene concentrations 10 17 g g oc 1 evidenced recent terrestrial and phytoplanktonic remains reworked in anaerobic conditions in these sediments organic carbon normalized concentrations of terrestrial alkanes and terpenoids were several fold higher than in the lobe sediments with lower accumulation rates sites a and f arguing for a more rapid degradation of terrestrial hydrocarbons than bulk organic carbon in the first steps of pre diagenesis ample variations in the contributions of biomarkers from higher plants ferns bacteria and angiosperms indicate an heterogeneous contribution of the soil and vegetation detritus delivered to the congo lobe sediments lower concentrations in terrestrial hydrocarbons at site e 45 km away from the active canyon indicated that river particles are still admixed to the dominant marine organic matter diploptene and hop 7 21 ene have a dual origin from terrestrial and marine microorganisms scatter in their relationship to gammacerene argues for a contribution of marine microorganisms in addition to soils sourced microorganisms the close distribution patterns of diploptene hop 21 ene hop 7 21 ene and neohop 13 18 ene is in line with the hypothesis of sequential clay catalyzed isomerisation of bacterial hopenes terrestrial biomarker accumulation fluxes at site c are one order of magnitude higher than vertical pelagic flux demonstrating the magnitude of the inputs delivered through turbiditic transport in the submarine canyon crude oil contamination was evidenced at the disconnected site e ucm c 21 to c 26 tricyclic diterpanes cpi and in smaller amounts in some sediments from sites a and c it may be related to marine crude oil extraction and transport a short chain mode of alkanes with an even predominance is evidenced in sediments of the lobe complex and likely sources crude oil microorganisms and ferns are discussed

origin and distribution of terrestrial organic matter in the nw mediterranean gulf of lions exploring the newly developed bit index the branched and isoprenoid tetraether bit index is based on the relative abundance of nonisoprenoidal glycerol dialkyl glycerol tetraethers gdgts derived from organisms living in terrestrial environments versus a structurally related isoprenoid gdgt crenarchaeol produced by marine crenarchaeota the bit index varies between 0 and 1 representing marine and terrestrial organic matter om end members respectively hopmans et al earth planet sci lett 224 107 116 2004 in this study the applicability of the bit index to trace terrestrial om is tested in combination with other organic parameters toc c n ratio 13corg total lipid and n alkane in the gulf of lions a river dominated continental margin of the western mediterranean we analyzed a variety of soils and riverbed sediments from the continent as well as surface sediments from the shelf and canyons the bit index in soils and riverbed sediments shows high values 0 9 while it varies between 0 02 and 0 83 in marine sediments decreasing seaward from the inner shelf to the slope for marine surface sediments high bit values are associated with lower 13corg values as well as higher toc contents and higher n alkane concentrations our results confirm that the bit index can be applied in coastal marine environments in order to characterize terrestrial om as proposed by hopmans et al 2004 therefore the bit index is a useful addition to the proxies presently available for studying the origin and distribution of om in continental margins and especially valuable in multiproxy studies

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

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

ichnofabric analysis of the shallow marine nukhul formation miocene suez rift egypt implications for depositional processes and sequence stratigraphic evolution abstract the shallow marine early syn rift miocene nukhul formation suez rift egypt is highly bioturbated and allows relationships between changes in trace fossils and ichnofabrics within a shallow marine depositional system to be documented and placed in a high resolution sequence stratigraphic framework seven ichnofabrics are present in a succession of interfingering calcareous mudstones and calcarenites forming coarsening up units of up to 30 m thick bounded by marine flooding surfaces the units grade upwards from a basal mudstone package with bed parallel concretions and a planolites chondrites ichnofabric offshore through a coarsening up succession of alternating calcarenites and mudstones with thalassinoides mottled sediment offshore transition ophiomorpha irregulaire lower shoreface ophiomorpha nodosa thalassinoides lower middle shoreface thalassinoides taenidium middle shoreface and o nodosa upper shoreface ichnofabrics gastrochaenolites hardground ichnofabric is separate as it is not genetically related to the other ichnofabrics ichnofabric development is primarily controlled by depositional environment e g bottom water oxygenation sediment type food abundance and energy level which control substrate colonisation sedimentation rate marine flooding surfaces are generally well cemented and marked by distinctive epifaunal and infaunal colonisation and can be traced out from proximal to distal settings over distances of 5 km the epifaunal colonisation in proximal settings consists of abundant oysters and corals with the substrate below marine flooding surfaces containing abundant thalassinoides and ophiomorpha isp abundance and diversity of epifauna and trace fossils and burrow size decreases distally into the basin in the most distal settings epifaunal colonisation is absent and only planolites and chondrites colonise the basinal mudstone marine flooding surfaces in the most distal settings are poorly cemented but are marked by carbonate concretions 10 15 cm below the surface

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

variability of tetraether lipids in yellow river dominated continental margin during the past eight decades implications for organic matter sources and river channel shifts abstract glycerol dialkyl glycerol tetraethers gdgts and bulk organic geochemical parameters were examined for a short core from the bohai sea a yellow river dominated continental margin a three end member mixing model using branched isoprenoid tetraethers bit index 13c and c n shows that the average fractions of soil marine and plant organic matter om during the period of 1933 2011 are 67 7 38 92 26 1 0 58 and 6 2 0 23 respectively abrupt changes of sedimentary om compositions around 1953 1976 and 1996 are synchronous with the yellow river mouth relocations the bit index values 0 33 0 80 present a stronger correlation with crenarchaeol abundance r2 0 88 than branched gdgts abundance r2 0 27 suggesting that variations of marine thaumarchaeota abundance rather than soil om inputs is the first order factor controlling the bit index values although this proxy has been widely used for soil om the comparison between the bit index nutrient status and historical yellow river sediment load indicates that the high sensitivity of the bit index to the yellow river channel shifts cannot be explained by a nutrient stimulation mechanism but instead is likely caused by the restriction of thaumarchaeota growth in highly turbid water due to the enormous sediment inputs from yellow river our study demonstrates that local conditions should be considered when applying the bit index as an environmental proxy

carbon isotopic compositions of prokaryotic lipids as tracers of carbon cycling in diverse settings recent work has highlighted the ubiquity of bacteria and archaea and continues to affirm their significance in diverse biogeochemical processes the 13c values and distributions of diagnostic lipids derived from such microorganisms can provide insights into prokaryotic processes in modern settings and are one of the few means by which past prokaryotic processes in depositional settings can be elucidated here we present a brief review of prokaryotic lipids commonly observed in sediments and the controls on their carbon isotopic compositions we then present two case studies one of mediterranean cold seeps at which anaerobic oxidation of methane occurs and one of a holocene peat deposit in which a variety of aerobic and anaerobic microorganisms govern the degradation of organic matter these two studies illustrate the potential utility of compound specific carbon isotope analyses to deconvolute pathways of carbon flow in microbial communities

transport and depositional process of soil organic matter during wet and dry storms on the tet inner shelf nw mediterranean article i nfo river floods and storm waves are major processes for the dispersal and deposition of terrestrial organic matter om in river dominated coastal areas a wet storm is connected to a flood with a high river discharge while a dry storm is not associated with a flood to better understand the sedimentation dynamics of terrestrial om especially soil om at the land ocean interface during wet and dry storms we studied sediment trap and core material collected on the tet inner shelf nw mediterranean using multiple organic proxies in combination with hydrodynamic parameters the proportion of soil om to the total om in the trap material calculated based on the bit branched and isoprenoid tetraether index was higher during both wet 40 and dry 30 storms than during non storm periods 10 however only surface sediments 1 cm thick layers recovered after december wet and moderate storms in 2003 showed enhanced soil om percentages compared to the deeper sediments deposited during the last century given that the wet storm eroded 4 cm of seabed at the study site flood induced fresh soil om was not deposited on the tet inner shelf during the wet storm however the following moderate storm caused resuspension of flood associated soil om which was previously trapped nearshore accordingly soil om was transported to the tet inner shelf and stored there until the dry storm occurred

spatial distributions of core and intact glycerol dialkyl glycerol tetraethers gdgts in the columbia river basin and willapa bay washington insights into origin and implications for the bit index abstract branched and isoprenoid glycerol dialkyl glycerol tetraethers brgdgts and isogdgts respectively are used to reconstruct carbon flow from terrestrial landscapes to the ocean in a proxy called the branched vs isoprenoid tetraether index or bit index the index is based on analysis of core gdgts c gdgts that are produced from intact gdgts i gdgts upon cell death gdgts are a component of the cell membranes of bacteria in soils br and archaea iso primarily in the marine environment however uncertainty as to the identity of the organisms that biosynthesize brgdgts the variation in the extent to which gdgts represent end member carbon pools and the suspected production of brgdgts and isogdgts in both marine and terrigenous environments hinders interpretation of the bit index since brgdgts remain our only tool for measuring the presence of unknown brgdgt producing organisms it is particularly important to use the intact form of brgdgts in living cells rather than c brgdgts in relict biomass to infer the distributions of the likely source organisms in situ production within riverine lacustrine and marine environments is currently thought to be possible yet few measures of i brgdgts are available in these environments to support these claims here we assess the spatial distribution of core and intact gdgts in the columbia river basin and nearby willapa bay washington and oregon in order to elucidate source environments and behavior of i gdgts vs c gdgts the presence of i brgdgts throughout the studied soils rivers and estuaries suggests in situ production across the continuum from soil to marine environments likewise intact crenarchaeol the marine end member isogdgt used in the bit index was present in all samples widespread production of each gdgt class along terrigenous carbon transport paths likely alters the bit index along this continuum core to intact ratios and the weak correlation between i gdgt derived bit values and carbon isotope signatures suggest a mixture of allochthonous and autochthonous sources of gdgts in riverine and marine environments our findings highlight the need for further work into the provenance and behavior of gdgts in order to improve interpretation of the bit index and other environmental proxies that rely on them

branched glycerol dialkyl glycerol tetraethers in arctic lake sediments sources and implications for paleothermometry at high latitudes branched glycerol dialkyl glycerol tetraethers brgdgts are analyzed in different lakes of the mackenzie canadian arctic and kolyma siberian arctic river basins to evaluate their sources and the implications for brgdgt based paleothermometry in high latitude lakes the comparison of brgdgt distributions and concentrations in the lakes with those in river suspended particulate matter riverbank sediments and permafrost material indicates that brgdgts in arctic lake sediments have mixed sources in contrast to global observations distributional offsets between brgdgts in arctic lakes and elsewhere in the catchment are minor likely due to the extreme seasonality and short window of biological production at high latitudes consequently both soil and lake calibrated brgdgt based temperature proxies return sensible temperature estimates even though the mean air temperature mat in the arctic is below the calibration range the original soil calibrated mbt cbt methylation of branched tetraethers cyclisation of branched tetraethers proxy generates mats similar to those in the studied river basins whereas using the recently revised mbt cbt calibration overestimates mat the application of the two global lake calibrations generating summer air temperatures sat and mat respectively illustrates the influence of seasonality on the production of brgdgts in lakes as the latter overestimates actual mat whereas the sat based lake calibration accounts for this influence and consequently returns more accurate temperatures our results in principle support the application of brgdgt based temperature proxies in high latitude lakes in order to obtain long term paleotemperature records for the arctic although the calibration and associated transfer function have to be selected with care

sources and distributions of tetraether lipids in surface sediments across a large river dominated continental margin glycerol dialkyl glycerol tetraether gdgt based proxies are increasingly used in modern carbon cycling and palaeoenvironmental investigations it is therefore crucial to examine the robustness sources transport and degradation of all gdgt based proxies in continental margins where sedimentation rates and extent of carbon cycling are high we have analyzed the distributions of gdgts in surface sediments from the lower yangtze river and east china sea ecs shelf the results revealed multiple sources and complex shelf processes that govern the distributions the isoprenoid gdgt inferred sea surface temperatures ssts are robust and reflect the satellite derived annual mean ssts on the shallow ecs shelf confirming an origin from surface water column dwelling crenarchaeota the input from methanogen sourced isoprenoid gdgts is significant in the river surface sediments but they are almost absent from the ecs shelf branched gdgts are also abundant in the river sediments but ca 95 are degraded in the yangtze estuary a much greater extent than observed for other terrigenous organic matter om proxies there is also evidence for production of branched gdgts in the oxic ecs shelf water column and the anoxic sediments waters of the lower yangtze river as a result branched gdgt based proxies in the lower river and ecs surface sediments do not reflect the catchment environmental conditions the effective degradation in the estuary and widespread aquatic contributions of branched gdgts improves our understanding of how to use branched gdgt based proxies in marginal seas

major changes in glacial and holocene terrestrial temperatures and sources of organic carbon recorded in the amazon fan by tetraether lipids the amazon basin is a major component of the global carbon and hydrological cycles a significant natural source of methane and home to remarkable biodiversity and endemism reconstructing past climate changes in the amazon basin is important for a better understanding of the effect of such changes on these critical functions of the basin using a novel biomarker proxy based on the membrane lipids of soil bacteria with a new regional calibration we present a reconstruction of changes in mean annual air temperatures for the amazon catchment during the last 37 kyr b p biomarkers were extracted from ocean drilling program sediment core odp942 recovered from the amazon fan the amazon fan is a major depository for terrestrial sediments with the advantage that the terrestrial material captured reflects a regional integration of the whole river catchment the reconstructed tropical amazonian temperatures were similar to 5 degrees c cooler at the last glacial maximum similar to 21 degrees c compared to modern values similar to 26 degrees c this is in agreement with previous estimates of tropical continental temperatures in the tropical amazon basin and tropical africa during the last glacial maximum moreover we also illustrate how the soil bacterial membrane lipid record reveals major changes in basin dynamics and sediment provenance during the glacial holocene transition impacting the biomarker reconstructions from similar to 11 kyr onward

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

a 30 ma history of the amazon river inferred from terrigenous sediments and organic matter on the ceara rise abstract the history of the amazon river is a much discussed subject and the timing of the development of a transcontinental system in particular is a matter of some controversy with estimations varying between the early miocene and the pliocene or even the pleistocene to shed further light on this we studied the sediment provenance of an oligocene to late pleistocene marine sedimentary section from the ceara rise odp site 925 a topographic high in the central atlantic ocean using major element concentrations and nd isotopic composition in 85 samples in addition the carbon isotopic composition of bulk organic matter and changes in the distribution of glycerol dialkyl glycerol tetraethers gdgts were used to identify periods of increased river outflow on the basis of these results we suggest that the history of the development of the amazon river is characterized by specific steps during the late oligocene early miocene 30 18 3 ma the terrigenous mass accumulation rates tars were high and sediment and gdgt compositions suggest that a large river system existed which at times received weathering products from a younger and probably andean sediment source a shift to a younger andean sediment provenance after 8 7 ma indicates that the amazon river became permanently connected with the andes between 18 3 and 4 5 ma tars were generally low and gdgts were derived for the most part from in situ production in marine waters around 4 5 ma the river expanded probably due to ongoing tectonic activity and uplift in the andes increased andean rock erosion this led to a strong increase in terrigenous sediment deposition and enhanced organic matter preservation on the ceara rise and the delivery of terrestrial both soil and riverine branched gdgts to the ceara rise

impact of riverine suspended particulate matter on the branched glycerol dialkyl glycerol tetraether composition of lakes the outflow of the selenga river in lake baikal russia branched glycerol dialkyl glycerol tetraethers brgdgts are bacterial membrane lipids found in several environments including soils rivers and lakes whose distribution varies with temperature and ph although this dependence is apparently not the same for the different environments mixing of brgdgt sources may thus complicate palaeoenvironmental reconstruction the extent to which brgdgts in a lake outflow reflect the distribution delivered by upstream rivers was studied for lake baikal russia one of the largest freshwater lakes worldwide fifteen brgdgts in suspended particulate matter spm of the selenga river and its outflow from the lake were quantified the river and lake spm had rather different distributions the riverine distribution was still apparent in the spm of the lake surface water 5 km from the river mouth but shifts in the distribution were already apparent in the spm of the surface water after 1 km based on the brgdgt distributions of the spm of the selenga outflow and that of the lake conservative mixing between the river and the lake brgdgt distributions could not fully explain the observed shifts in distributions both preferential degradation and in situ production of brgdgts in the surface and especially bottom water of the river outflow were potentially responsible this implies that a riverine lipid distribution delivered to a lake can be modified prior to being transported downstream the lacustrine brgdgt distribution that possibly could have reflected a mixture of mountainous and selenga river spm was not recognized in downstream yenisei river spm the watershed of lake baikal thus does not seem to contribute to the brgdgts transported to the marine system as many large rivers have major lakes in their watershed this has implications for palaeoclimate reconstruction from river fan sediments globally

sources and transport of terrestrial organic matter in vancouver island fjords and the vancouver washington margin a multiproxy approach using d13corg lignin phenols and the ether lipid bit index the branched and isoprenoid tetraether bit index a ratio of marine and terrestrial glycerol dialkyl glycerol tetraether gdgt membrane lipids was recently introduced as a proxy for the fraction of fluvially derived organic carbon oc buried in marine sediments we investigate the source and distribution of terrestrial oc in marine sediments in a large spatial data set that encompasses the washington vancouver island margin vancouver island fjords and puget sound with the goal of comparing the bit index to other traditional measures of terrestrial oc d13 co f oc d13corg and lignin phenols d13corg values and lignin concentrations indicate that the fjords are a significant trap for undegraded wood derived terrestrial material with surface sediments containing up to 76 terrestrial oc these proxies also show significant terrestrial oc contributions to margin sediments up to 54 with most likely an angiosperm source from the columbia river in contrast to d13corg values and lignin concentrations bit index values indicate extremely low terrestrial carbon throughout the study area bit index values range from 0 to 0 28 and are uncorrelated with the other proxies though the bit index did not correlate with other proxies margin gdgt concentrations varied offshore similarly to other terrestrially derived oc and are well correlated with other proxies we suggest that the bit index is best interpreted as a proxy for soil or peat derived oc the majority of terrestrially derived oc delivered to sediment in this area has a lignin rich nonsoil source the disparity between the bit index and other proxies implies that the bit index significantly underestimates terrestrial relative to marine oc input to sediments in areas in which riverine oc input is not soil or peat derived burial of organic carbon oc on continental margins is estimated to account for the majority of the total carbon burial in the ocean and is a significant sink for terrestrial oc hedges and keil 1995 understanding the sources and fate of this terrestrial oc in marine sediments is thus of importance in understanding global biogeochemical cycles in this study we use two traditional proxies for terrestrial oc input to sediments the d 13 c of bulk sedimentary oc d13corg and the concentration of lignin phenols to examine the sources and quantity of terrestrial oc in sediments throughout the washington vancouver island margin vancouver island fjords and puget sound we compare these results to those obtained using a recently introduced proxy for terrestrial oc in marine sediments the branched and isoprenoid tetraether bit index

spatial heterogeneity of sources of branched tetraethers in shelf systems the geochemistry of tetraethers in the berau river delta kalimantan indonesia abstract the bulk organic matter composition total organic carbon toc content and 13ctoc and composition of isoprenoid and branched glycerol dialkyl glycerol tetraethers gdgt in surface sediments from 43 stations in the berau river delta east kalimantan indonesia including two coast shelf transects and stations within the river mouth were examined to reveal the spatial heterogeneity in these parameters in order to assess the impact of a tropical river loaded with suspended matter on the sedimentary organic matter in the shelf system the high resolution study showed that despite the extensive transport of eroded soil material by the river to the sea terrestrial organic matter and brgdgts are only deposited on a relatively small part of the shelf the concentrations of brgdgts are highest up to 120 g g 1 toc in sediments deposited in and close to the mouth of the berau river and their distribution indicates that they represent a mixture of soil derived and river in situ produced brgdgts crenarchaeol concentrations reach 700 g g 1 toc in sediments deposited on the outer shelf due to thaumarchaeotal production in shelf waters this results in a strong gradient 0 93 0 03 in the bit index with high values in the river mouth and low values on the shelf the decline in the bit index is caused by both decreasing concentrations of the brgdgts and increasing concentrations of crenarchaeol the bit index shows a highly significant but non linear relationship with 13ctoc on the shelf in the area not under the direct influence of the berau river cyclic brgdgts become relatively dominant most probably due to in situ production in the alkaline pore waters of the surface sediments the spatial heterogeneity of sources of brgdgts on the berau shelf complicates the use of brgdgts as temperature proxies application of the global soil calibration to sedimentary mixtures of brgdgts in the river influenced area of the shelf results in a severe underestimation of mean annual air temperature mat by 6 c this is due to the mixed origin of the brgdgts which are not only derived from soil erosion but likely also from riverine production as has been observed for other river systems comparison of the berau shelf other shelf systems indicates that in situ production of brgdgts in shelf sediments is a widespread phenomenon that is especially pronounced at water depths of ca 50 300 m it is hypothesized that this is so because benthic in situ production of heterotrophic brgdgt producing bacteria is fueled by the higher delivery of fresh organic matter to these sediments as the consequence of higher primary productivity in shelf waters and a decreased mineralization due to the relatively short settling times of particles on the shelf for palaeoclimatic studies of marine shelf sediments the application of brgdgts as proxies is severely complicated by the heterogeneity of sources of brgdgts comparison of the brgdgt composition of soils with those of shelf sediments may assist in deciding if sedimentary brgdgts are predominantly derived from soil erosion several methods to do so are discussed

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

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

sources of organic matter in changjiang yangtze river bed sediments preliminary insights from organic geochemical proxies insight into the content and composition of organic carbon oc in river systems contributes to our understanding of the global carbon cycle the changjiang yangtze river plays a significant role in global carbon and hydrological cycles as it is an important supplier of sediment nutrients and oc to the east china sea to provide a preliminary insight into the source of oc transported by the changjiang we analyzed bulk grain size organic carbon content 13c and molecular lignin phenols branched and isoprenoid gdgts characteristics of organic matter in bed sediments at eight locations along the river the 13c values and lignin phenol composition indicate that the oc originates from a mixture of primarily soils and plants comparison between branched gdgt br gdgt distributions in riverbed sediments and those in the different soil types in the drainage basin indicate that the br gdgt signal in the upper reaches is largely derived from soils from the qinghai tibet plateau downstream changes in br gdgt distributions can be linked to subsequent input of local soil material the observed variation in br gdgt composition along the river implies that a portion of the oc may be oxidized or replaced by the local input during transit although the relationship between 13c and lignin phenol composition indicates that the contribution of phytoplankton is limited comparison of gdgt ratios gdgt 0 crenarchaeol iso gdgts br gdgts bit index for the sediments and surrounding soils indicates that at least part of the iso gdgts has an aquatic origin overall the downstream evolution of br gdgts in the changjiang implies that their use as paleoclimate proxy in downcore applications will likely yield a local rather than a basin integrated continental climate record

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

characterization of transport and deposition of terrestrial organic matter in the southern north sea using the bit index we have applied a recently introduced proxy the bit branched and isoprenoid tetraether index to determine terrestrial organic matter tom transport from the rivers rhine and meuse and their tributaries to the southern north sea this index is based on crenarchaeol an isoprenoidal glycerol dialkyl glycerol tetraether gdgt predominantly derived from aquatic crenarchaeota and branched gdgts produced by soil bacteria up to 1 6 ng l 1 of branched gdgts were measured in seawater demonstrating the presence of tom in the southern north sea bit indices were inversely correlated with salinity indicating that this tom was recently supplied by rivers the substantial amount of branched gdgts 35 ng l 1 detected in river water and the high branched gdgt concentration measured in the water of a swiss peat bog 5 900 ng l 1 suggest fluvial transport of branched gdgts from peats and soils to the oceans the high crenarchaeol concentration measured in river water 4 4 ng l 1 was probably derived from crenarchaeota living in rivers and organic material from soil and peat the bit index 13c value and c n ratio of surface sediments deposited in the southern north sea were compared to determine tom deposition bit index 0 07 to 0 26 and d13c 220 6 to 222 9 both showed substantial small scale differences in tom deposition in the southern north sea but this pattern was not obvious from the c n ratios a good correlation was found between 13c and branched gdgt concentrations indicating that the absolute gdgt concentrations give additional information to the bit index

sources and distributions of branched and isoprenoid tetraether lipids on the amazon shelf and fan implications for the use of gdgt based proxies in marine sediments branched glycerol dialkyl glycerol tetraethers brgdgts in river fan sediments have been used successfully to reconstruct mean annual air temperature maat and soil ph of the congo river drainage basin however in a previous study of amazon deep sea fan sediments the reconstructed maats were ca 10 c colder than the actual maat of the amazon basin in this study we investigated this apparent offset by comparing the concentrations and distributions of brgdgts in amazon river suspended particulate matter spm and sediments to those in marine spm and surface sediments the riverine brgdgt input was evident from the elevated brgdgt concentrations in marine spm and surface sediments close to the river mouth the distributions of brgdgts in marine spm and sediments varied widely but generally showed a higher relative abundance of methylated and cyclic brgdgts than those in the river since this difference in brgdgt distribution was also found in intact polar lipid ipl derived brgdgts which were more recently produced the change in the marine brgdgt distribution was most likely due to marine in situ production consequently the maats calculated based on the methylation of branched tetraethers mbt and the cyclisation of branched tetraethers cbt were lower and the cbt derived ph values were higher than those of the amazon basin however spm and sediments from stations close to the river mouth still showed mbt cbt values that were similar to those of the river therefore we recommend caution when applying the mbt cbt proxy it should only be used in sediment cores that were under high river influence the influence of riverine derived isoprenoid gdgt isogdgt on the isogdgt based tex86 temperature proxy was also examined in marine spm and sediments an input of riverine isogdgts from the amazon river was apparent but its influence on the marine tex86 was minor since the tex86 of spm in the amazon river was similar to that in the marine spm and sediments

exchanges of sediment between the flood plain and channel of the amazon river in brazil sediment transport through the brazilian sector of the amazon river valley a distance of 2010 km involves exchanges between the channel and the flood plain that in each direction exceed the annual flux of sediment out of the river at obidos 1200 mt yr 1 the exchanges occur through bank erosion bar deposition settling from diffuse overbank flow and sedimentation in flood plain channels we estimated the magnitude of these exchanges for each of 10 reaches of the valley and combined them with calculations of sediment transport into and out of the reaches based on sediment sampling and flow records to define a sediment budget for each reach residuals in the sediment budget of a reach include errors of estimation and erosion or deposition within the channel the annual supply of sediment entering the channel from bank erosion was estimated to average 1570 mt yr 1 1 3 the obidos flux and the amount transferred from channel transport to the bars 380 mt yr 1 and the flood plain 460 mt yr 1 in channelized flow 1230 mt yr 1 in diffuse overbank flow totaled 2070 mt yr 1 1 7 the obidos flux thus deposition on the bars and flood plain exceeded bank erosion by 500 mt yr 1 over a 10 16 yr period sampling and calculation of sediment loads in the channel indicate a net accumulation in the valley floor of approximately 200 mt yr 1 over 16 yr crudely validating the process based calculations of the sediment budget which in turn illuminate the physical controls on each exchange process another 300 400 mt yr 1 are deposited in a delta plain downstream of obidos the components of the sediment budget reflect hydrologic characteristics of the valley floor and geomorphic characteristics of the channel and flood plain which in turn are influenced by tectonic features of the amazon structural trough

impact of river channel shifts on tetraether lipids in the rhone prodelta nw mediterranean implication for the bit index as an indicator of palaeoflood events we tested the applicability of the bit branched and isoprenoid tetraether index as a proxy for palaeoflood events in the river dominated continental margin of the gulf of lions nw mediterranean we compared the concentrations of branched glycerol dialkyl glycerol tetraethers br gdgts and crenarchaeol in suspended particulate matter spm collected downstream in the rhone river as well as in surface sediments and a ca 8m piston core from the rhone prodelta the core covered the last 400 yr with four distinct intervals recording the river influence under natural and man induced shifts in four main channels of the river mouth bras de fer grand rhone pegoulier and roustan the results indicate that there are mixed sources of br gdgts and crenarchaeol in the prodelta complicating applicationof the bit index as an indicator of continental organic carbon input and thus as a palaeoflood proxy however the sedimentary bit record for the period when continental material was delivered by the river more directly to the core site roustan phase 1892 to present mimics the historical palaeoflood record this shows the potential of the bit index as a palaeoflood proxy provided that the delivery route of the continental material by rivers to the core sites remains constant over time the study also highlights the idea that shifts in river channels should be taken into account for the use of the bit index as a palaeoflood proxy

tracing soil organic carbon in the lower amazon river and its tributaries using gdgt distributions and bulk organic matter properties abstract in order to trace the transport of soil organic carbon oc in the lower amazon basin we investigated the distributions of crenarchaeol and branched glycerol dialkyl glycerol tetraethers gdgts by analyzing riverbed sediments and river suspended particulate matter spm collected in the solimoes amazon river mainstem and its tributaries the branched and isoprenoid tetraether bit index a proxy for river transported soil oc into the ocean was determined from the distributions of these gdgts the gdgt derived parameters were compared with other bulk geochemical data i e c n ratio and stable carbon isotopic composition the gdgt derived and bulk geochemical data indicate that riverine spm and riverbed sediments in the lower amazon river and its tributaries are a mixture of c3 plant derived soil oc and aquatic derived oc the branched gdgts in the spm and riverbed sediments did not predominantly originate from the high andes soils 2500 m in altitude as was suggested previously however further constraint on the soil source area of branched gdgts was hampered due to the deficiency of soil data from the lower montane forest areas in the andes our study also revealed seasonal and interannual variation in gdgt composition as well as soil oc discharge which was closely related to the hydrological cycle by way of a simple binary mixing model using the flux weighted bit values at obidos the last gauging station in the amazon river we estimated that 70 80 of the poc pool in the river was derived of soil oc however care should be taken to use the bit index since it showed a non conservative behaviour along the river continuum due to the aquatic production of crenarchaeol further investigation using a continuous sampling strategy following the full hydrological cycle is required to fully understand how soil derived gdgt signals are transformed in large tropical river systems through their transport pathway to the ocean

selective preservation of soil organic matter in oxidized marine sediments madeira abyssal plain in ocean margin sediments both marine and terrestrial organic matter om are buried but the factors governing their relative preservation and degradation are not well understood in this study we analysed the degree of preservation of marine isoprenoidal and soil derived branched glycerol dialkyl glycerol tetraethers gdgts upon long term oxygen exposure in om rich turbidites from the madeira abyssal plain by analyzing gdgt concentrations across oxidation fronts relative to the anoxic part of the turbidites ca 7 20 of the soil derived branched gdgts were preserved in the oxidized part while only 0 2 3 of the marine isoprenoid gdgt crenarchaeol was preserved due to these different preservation factors the branched isoprenoid tetraether bit index a ratio between crenarchaeol and the major branched gdgts that is used as a tracer for soil derived organic matter substantially increases from 0 02 to 0 4 split flow thin cell splitt separation of turbidite sediments showed that the enhanced preservation of soil derived carbon was a general phenomenon across the fine particle size ranges 38 m calculations reveal that despite their relatively similar chemical structures degradation rates of crenarchaeol are 2 fold higher than those of soil derived branched gdgts suggesting preferential soil om preservation possibly due to matrix protection

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

disentangling marine soil and plant organic carbon contributions to continental margin sediments a multi proxy approach in a 20 000 year sediment record from the congo deep sea fan abstract a 20 kyr long sediment sequence from the congo deep sea fan core geob 6518 1 one of the world s largest deep sea river fans has been analysed for bulk and molecular proxies in order to reconstruct the marine soil and plant organic carbon oc contributions to these sediments since the last glacial maximum the bulk proxies applied c n ratio and 13 c org ranged from 10 to 12 5 and from 24 5 to 21 vpdb respectively as molecular proxies concentrations of marine derived alkenones and terrestrial derived odd numbered n alkanes were used which varied between 0 2 and 4 g g dry weight sediment in addition the branched vs isoprenoid tetraether bit index a proxy for soil organic matter input was used which varied from 0 3 to 0 5 in this core application of binary mixing models based on the different individual proxies showed estimates for terrestrial oc input varying by up to 50 due to the heterogeneous nature of the oc application of a three end member mixing model using the 13 c org content the c n ratio and the bit index enabled the distinction of soil and plant organic matter as separate contributors to the sedimentary oc pool the results show that marine oc accounts for 20 to 40 of the total oc present in the deep sea fan sediments over the last 20 kyr and that soil oc accounts for about half 45 on average of the oc present this suggests that soil oc represents the majority of the terrestrial oc delivered to the fan sediments accumulation rates of the plant and soil oc fractions over the last 20 kyr varied by a factor of up to 5 and are strongly related to sediment accumulation rates they showed an increase starting at ca 17 kyr bp a decline during the younger dryas peak values during the early holocene and lower values in the late holocene this pattern matches with reconstructions of past central african humidity and congo river discharge from the same core and revealed that central african precipitation patterns exert a dominant control on terrestrial oc deposition in the congo deep sea fan marine oc accumulation rates are only weakly related to sediment accumulation rates and vary only little over time compared to the terrigenous fractions these variations are likely a result of enhanced preservation during times of higher sedimentation rates and of relative small fluctuations in primary production due to wind driven upwelling

a mineralogical and organic geochemical overview of the effects of holocene changes in amazon river flow on three floodplain lakes abstract a synthesis of the impacts of the amazon river hydrological changes on the sedimentation process of organic matter om in three different floodplain lakes santa ninha maraca and comprido lakes is presented in this study today the santa ninha and maraca lakes are directly and permanently connected with the main channel of the amazon river in contrast to comprido lake which is indirectly and periodically influenced by the amazon river due to its greater distance from the main channel all three lake sediment records showed a reduced river inflow due to dry climatic conditions during the early and middle holocene followed by an increased fluvial input during the wetter late holocene in santa ninha and maraca lakes the reduced river inflow period was recorded by sediments with a low abundance of smectite on average 20 wt a clay mineral mainly transported by the fluvial system high total organic carbon toc contents on average 8 2 wt and a predominantly acidic soil om input evidenced by high concentrations on average 180 g gtoc 1 of branched glycerol dialkyl glycerol tetraethers gdgt during the late holocene a higher smectite abundance on average 43 wt and a lower toc content on average 1 4 wt pointed to greater dilution by riverine lithogenic matter this change was accompanied by a proportional increase in the aquatically produced crenarchaeol suggesting a higher lake water level in comprido lake a sedimentation gap occurred during the early and middle holocene the wetter late holocene since 3000 cal years bp was characterized by high toc values on average 9 wt and a sharp increase in soil om input as recorded by an increase in branched gdgt concentrations on average 81 g gtoc 1 but the smectite content was low on average 14 this combination suggests that the soil om input to comprido lake from the local catchment area became dominant during the wet climate late holocene due to the large distance of the lake from the amazon river main channel consequently our study shows that the sedimentation processes of om in amazonian floodplain lakes were strongly influenced by variations in the hydrodynamic regime of the amazon river during the holocene however the impacts of the variations on the three floodplain lakes were different depending on the distance of each lake from the main channel of the amazon river

climatic and geomorphic drivers of plant organic matter transport in the arun river e nepal fixation of atmospheric co2 in terrestrial vegetation and subsequent export and deposition of terrestrial plant organic matter in marine sediments is an important component of the global carbon cycle yet it is difficult to quantify this is partly due to the lack of understanding of relevant processes and mechanisms responsible for organic matter transport throughout a landscape here we present a new approach to identify terrestrial plant organic matter source areas quantify contributions and ascertain the role of ecologic climatic and geomorphic controls on plant wax export in the arun river catchment spanning the world s largest elevation gradient from 205 to 8848 m asl in eastern nepal our approach takes advantage of the distinct stable hydrogen isotopic composition expressed as d d values of plant wax n alkanes produced along this gradient transported in river waters and deposited in flood deposits alongside the arun river and its tributaries in mainstem flood deposits we found that plant wax n alkanes were mostly derived from the lower elevations constituting only a small fraction 15 of the catchment informed by remote sensing data we tested four differently weighted isotopic mixing models that quantify sourcing of tributary plant derived organic matter along the arun and compare it to our field observations the weighting parameters included catchment area net primary productivity npp and annual rainfall amount as well as catchment relief as erosion proxy when weighted by catchment area the isotopic mixing model could not explain field observations on plant wax d d values along the arun which is not surprising because the large arid tibetan plateau is not expected to be a major source weighting areal contributions by annual rainfall and npp captured field observations within model prediction errors suggesting that plant productivity may influence source strength however weighting by a combination of rainfall and catchment relief also captured the observed d d value pattern suggesting dominantly erosive control we conclude that tributaries at the southern himalayan front with high rainfall high productivity high relief and high erosion rates dominate plant wax exports from the catchment

twentieth century proxy records of temperature and soil organic matter input in the drammensfjord southern norway abstract the drammensfjord in southern norway is an enclosed anoxic basin with a laminated sedimentary record the fjord is a transition area between the marine and terrestrial environments and thus its sedimentary archive contains information on both environments in order to reconstruct recent environmental changes in southern norway two sediment cores covering the last 90 years were analyzed we used the branched versus isoprenoid tetraether bit index as an indicator of terrestrial organic mater input and compared it to the stable carbon isotopic composition of total organic carbon 13 c toc the 13 c toc and bit index show opposing trends with 13 c toc indicating an increase in terrestrial input while the bit index suggests a decrease towards the present this contradiction is probably due to the different sources reflected by 13 c toc vegetation soil and anthropogenic input and the bit index only soil organic matter input in addition an increase in the recycling of respired co 2 within the fjord s water column could have depleted the 13 c toc of the marine component towards more negative values thus seemingly indicating an increase in terrestrial input whilst the bit index could have been affected by a reduction of riverine input and or an increase in archaeal biomass production the tetraether index of lipids with 86 carbons tex 86 was determined as a proxy for past water surface temperatures while some of the signal could be coming from the chemocline our results suggest that tex 86 indicates surface upper 25 m temperatures moreover tex 86 temperature patterns seem to follow variations in the historical record of averaged spring to fall oslo air temperature relatively closely suggesting the signal is produced during this period therefore tex 86 temperature records of fjord sediment cores can potentially be a useful tool in reconstructing past variations of coastal climates

an unusual isoprenoid tetraether lipid in marine and lacustrine sediments abstract recent studies have shown that glycerol dialkyl glycerol tetraether gdgt lipids thought be unique for hyper thermophilic archaea are also present in non thermophilic archaea and environments in this study an unusual h shaped isoprenoid gdgt in which the two biphytanyl carbon skeletons are covalently bound by a carbon carbon bond was unambiguously identified in a number of sediments from marine and lacustrine environments its abundance varies from 0 2 to 6 of isoprenoid gdgts the h shaped isoprenoid gdgt was originally identified in hyperthermophilic archaea and its presence in marine and lacustrine sediments suggests it is also synthesized by certain non thermophilic relatives possibly euryarchaeota

origin of particulate organic carbon in the upper st lawrence isotopic constraints abstract seven sampling locations in the upper st lawrence river near the city of cornwall ontario canada including the main river and six near shore ecosystems a creek embayments and a wetland were studied in order to determine the origin of particulate organic carbon parameters studied included chlorophyll a chl a particulate organic carbon poc and dissolved inorganic carbon dic as well as the isotopic compositions of the latter two 13cpoc 13cdic the results show that in situ photosynthesis and detrital inputs are both significant contributors to the poc pool in the isolated embayments the former dominates during warm seasons with poc concentrations up to 2663 g l and chl a concentrations up to 26 1 g l near shore ecosystems have a wide range of 13cpoc values 31 5 to 16 3 but this variability is not reflected in the main channel there the 13cpoc signal is uniformly close to 27 in accord with estimates from earlier studies on the river s estuary this suggests that the poc contribution from near shore ecosystems is minor although the main channel has low chl a concentrations model calculations suggest that most of its poc originates from photosynthetic activity probably within the great lakes

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

sedimentology and paleoecology of upper ordovician mounds of anticosti island quebec relatively thin organic buildups in the ellis bay formation of anticosti island developed in a shallow subtidal regressive marine shelf environment during the late ordovician the ellis bay formati

inland variability of carbon nitrogen concentrations and δ13c in amazon floodplain varzea vegetation and sediment we analysed carbon nitrogen and 13c values in sediment sampled in the amazon floodplains the surface sediment samples were collected along inland transects divided according to their vegetation cover a forest where the dominant vegetation was inundation forests b grass where the dominant vegetation was grasses mainly from echnochloa polystachya c mixed where the vegetation changed from grasses near the river bank to forest inland the average sediment carbon and nitrogen concentrations were significantly higher in forest samples c 0 99 n 0 12 than in grass samples c 0 84 n 0 10 the average sediment 13c was significantly heavier in grass 26 7 than in forest samples 28 6 reflecting the isotopically heavier c4 grasses carbon in the forest and mixed transects inland increases in the carbon and nitrogen concentrations were observed at approximately 50 to 60 m from the riverbank the concentration of carbon and nitrogen became similar to the river particulate organic carbon poc concentration which is the primary floodplain sediment source we hypothesized that this trend is caused by the deposition of carbon and nitrogen depleted sand size particles in the first few metres of the floodplain whereas the more enriched silt clay particles are preferentially deposited far inland in contrast to inland trends no significant downriver trend was observed in the carbon and nitrogen concentrations however a downriver 13c increase was observed for sediment in grass covered areas based on 13c values in different varzea environments we estimated the relative contribution of riverine poc and vegetation material present in the varzea sediments under different vegetation covers for forest sediment samples we estimated that 60 of the carbon was derived from the riverine poc and the forests provided the remaining 40 for open areas covered with grasses we estimated that only 10 was derived from these plants and 90 was derived from riverine poc copyright 2003 john wiley sons ltd