diagenetic and catagenetic products of isorenieratene molecular indicators for photic zone anoxia a wide range of novel diagenetic and catagenetic products of the diaromatic carotenoid isorenieratene a pigment of the photosynthetic green sulphur bacteria chlorobiaceae has been identified in a number of sedimentary rocks ranging from ordovician to miocene compound identification is based on nmr mass spectrometry the presence of atropisomers and stable carbon isotopes atropisomers contain an axially chiral centre which in combination with other chiral centres results in two or more diastereomers that can be separated on a normal gc column chlorobiaceae use the reverse tca cycle to fix carbon so that their biomass is enriched in 13c high 13c contents of isorenieratene derivatives therefore support their inferred origins isorenieratene derivatives include c 40 c 33 and c 32 diaryl isoprenoids and short chain aryl isoprenoids with additional aromatic and or s containing rings c 33 and c 32 compounds are diagenetic products of c 33 and c 32 carotenoids formed from isorenieratene during early diagenesis through expulsion of toluene and m xylene respectively cyclisation of the polyene acyclic isoprenoid chain can proceed via an intramolecular diels alder reaction followed by aromatisation of the newly formed ring sulphurisation is also an important process during early diagenesis competing with expulsion and cyclisation sulphur bound isorenieratane is released during progressive diagenesis due to cleavage of relatively weak ss and cs bonds cleavage of c c bonds during aromatisation of newly formed rings and during catagenesis yields short chain compounds the inherent presence of a conjugated double bond system in carotenoids implies that similar diagenetic and catagenetic reactions can occur with all carotenoids chlorobiaceae live at or below the oxic anoxic boundary layer and require both light and h 2s the presence of isorenieratene or its diagenetic and catagenetic products in ancient sedimentary rocks and crude oils is therefore an excellent indication for photic zone anoxia in the depositional environment diagenetic and catagenetic products of isorenieratene are expected to find applications in reconstruction of palaeoenvironments and in oil oil and oil source rock correlation studies their presence in several petroleum source rocks suggests that anoxia is an important environmental parameter for the preservation of organic matter

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

archaeal tetraether membrane lipid fluxes in the northeastern pacific and the arabian sea implications for tex86 paleothermometry the newly introduced temperature proxy the tetraether index of archaeal lipids with 86 carbon atoms tex86 is based on the number of cyclopentane moieties in the glycerol dialkyl glycerol tetraether gdgt lipids of marine crenarchaeota the composition of sedimentary gdgts used for tex86 paleothermometry is thought to reflect sea surface temperature sst however marine crenarchaeota occur ubiquitously in the world oceans over the entire depth range and not just in surface waters we analyzed the gdgt distribution in settling particulate organic matter collected in sediment traps from the northeastern pacific ocean and the arabian sea to investigate the seasonal and spatial distribution of the fluxes of crenarchaeotal gdgts and the origin of the tex86 signal transported to the sediment in both settings the tex86 measured at all trap deployment depths reflects sst in the arabian sea analysis of an annual time series showed that the sst estimate based on tex86 in the shallowest trap at 500 m followed the in situ sst with a 1 to 3 week time delay likely caused by the relatively low settling speed of sinking particles this revealed that the gdgt signal that reaches deeper water is derived from the upper water column rather than in situ production of gdgts the gdgt temperature signal in deeper traps at 1500 m and 3000 m did not show a seasonal cyclicity observed in the 500 m trap but rather reflected the annual mean sst this is probably due to a homogenization of the tex86 sst signal carried by particles as they ultimately reach the interior of the ocean our data confirm the use of tex86 as a temperature proxy of surface ocean waters

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

long chain alkenones in qinghai lake sediments abstract long chain methyl and ethyl alkenones c 37 c 40 containing two to four double bonds have been detected in sediments from qinghai lake china this is the first report of the alkenones in lake sediments deposited under a variety of salinity conditions where the lake has not encountered any marine incursions the presence of the alkenones suggests the presence of prymnesiophyceae in the lake which may have reached the lake via eolian transportation or seabirds sediment samples from the more saline areas of the lake contained higher concentrations of the more highly unsaturated compounds widespread use of these compounds as paleotemperature indicators in marine sediments introduces the possibility of extrapolating this approach to lacustrine environments if appropriate calibrations can be undertaken

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

coherence between tropical east african and south american records of the little ice age 1 comparison of high resolution paleoclimate records from lake malawi and the cariaco basin reveals a consistent tropical behavior during the little ice age these records which are interpreted to represent southward excursions of intertropical convergence zone position over southern tropical east africa and northeastern south america are characterized by subcentennial variability superimposed on a ramp of increasing intensity from ce 1400 to 1800 this response appears similar to that of cold episodes during the late glacial the synchrony of these records suggests a teleconnection in tropical climate that may be a manifestation of persistent enso like conditions

applicability and calibration of the tex86 paleothermometer in lakes abstract we have conducted a global survey of archaeal glycerol dialkyl glycerol tetraether gdgt lipids in lake sediments in order to develop the tex86 paleotemperature proxy for application in continental systems surface sediments of 46 globally distributed lakes were analyzed for gdgt but isoprenoid gdgt derived from aquatic crenarchaeota were only unambiguously detected in 20 of the 46 lakes analyzed aquatic crenarchaeotal gdgt were detected mainly in sediments from large lakes 4000 km2 and hydrothermal or volcanic lakes suggesting that in some mostly smaller lakes either aquatic crenarchaeota are present at low abundance resulting in sedimentary lipids below levels of detection or they are absent branched gdgt thought to be derived primarily from soil bacteria were identified in all lake sediments analyzed correlation of the tex86 in those lakes with sufficient amounts of putative crenarchaeotal gdgt with annual mean lake temperature is reasonably good r2 0 68 n 20 in order to reduce the influence of soil derived isoprenoid gdgt on the tex86 lake temperatures we have applied a filter based on relative soil derived inputs as determined by the bit branched and isoprenoid tetraether index which results in a calibration relationship with r2 0 86 n 12 and an estimated temperature error of 3 6 c our results suggest that the tex86 should be applied only in lakes with sufficient production of gdgt by aquatic crenarchaeota relative to isoprenoid gdgt derived from soil in the watershed or other aquatic sources

molecular fossil evidence for anaerobic ammonium oxidation in the arabian sea over the last glacial cycle anaerobic ammonium oxidation anammox has been recognized as an important process converting fixed nitrogen to n2 in many marine environments thereby having a major impact on the present day marine nitrogen cycle however essentially nothing is known about the importance of anammox in past marine nitrogen cycles in this study we analyzed the distribution of fossil ladderane lipids derived from bacteria performing anammox in a sediment core from the northern arabian sea concentrations of ladderane lipids varied between 0 3 and 5 3 ng g 1 sediment during the past 140 ka with high values observed during the holocene intervals during the last glacial and during the penultimate interglacial maxima in ladderane lipid abundances correlate with high total organic carbon 4 6 and elevated 15n 8 values anammox activity therefore seems enhanced during periods characterized by an intense oxygen minimum zone omz low concentrations of ladderanes 0 5 ng g 1 sediment indicating low anammox activity coincide with periods during which the omz was severely diminished since anammox activity covaried with omz intensity it may play an important role in the loss of fixed inorganic nitrogen from the global ocean on glacial interglacial timescales which was so far attributed only to heterotrophic denitrification

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

combined dna and lipid analyses of sediments reveal changes in holocene haptophyte and diatom populations in an antarctic lake preserved ribosomal dna of planktonic phototrophic algae was recovered from holocene anoxic sediments of ace lake antarctica and the ancient community members were identified based on comparative sequence analysis the similar concentration profiles of dna of haptophytes and their traditional lipid biomarkers alkenones and alkenoates revealed that fossil rdna also served as quantitative biomarkers in this environment the dna data clearly revealed the presence of six novel phylotypes related to known alkenone and alkenoate biosynthesizing haptophytes with isochrysis galbana uio 102 as their closest relative the relative abundance of these phylotypes changed as the lake chemistry particularly salinity evolved over time changes in the alkenone distributions reflect these population changes rather than a physiological response to salinity by a single haptophyte using this novel paleo ecological approach of combining data from lipid biomarkers and preserved dna we showed that the post glacial development of ace lake from freshwater basin to marine inlet and the present day lacustrine saline system caused major qualitative and quantitative changes in the biodiversity of the planktonic populations over time

aging of marine organic matter during cross shelf lateral transport in the benguela upwelling system revealed by compound specific radiocarbon dating organic matter accumulation and burial on the namibian shelf and upper slope are spatially heterogeneous and strongly controlled by lateral transport in subsurface nepheloid layers much of the material deposited in depo centers on the slope ultimately derives from the shelf supply of organic matter from the shelf involves selective transport of organic matter we studied these selective transport processes by analyzing the radiocarbon content of co occurring sediment fractions here we present radiocarbon data for total organic carbon as well as three tracers of surface ocean productivity phytoplankton derived alkenones membrane lipids of pelagic crenarchaeota crenarchaeol and calcareous microfossils of planktic foraminifera in core top and near surface sediment samples the samples were collected on the namibian margin along a shelf slope transect 85 to 1040 m at 24 s and from the upper slope depo center at 25 5 s in core top sediments alkenone ages gradually increased from modern to 3490 radiocarbon years with distance from shore and with water depth crenarchaeol while younger than alkenones also increased in age with distance offshore it was concluded that the observed ages were a consequence of cross shelf transport and associated aging of organic matter radiocarbon ages of preserved lipid biomarkers in sediments thus at least partially depend on the relative amount of laterally supplied pre aged material present in a sample highlighting the importance of nepheloid transport for the sedimentation of organic matter over the namibian margin

millennial scale sea surface temperature changes in the eastern mediterranean nile river delta region over the last 27 000 years 1 in this study we utilize two organic geochemical proxies the u37k index and tex86 to examine past sea surface temperatures sst from a site located near the nile river delta in the eastern mediterranean em sea the u37k and tex86 records generally are in agreement and indicate sst ranges of 14 c 26 c and 14 c 28 c respectively during the last 27 cal ka during the holocene tex86 based sst estimates are usually higher than u37k based sst estimates which is likely due to seasonal differences between the timing of the haptophyte and crenarchaeota blooms in the em and is related to the onset of the modern flow regime of the nile river both records show that sst varied on centennial to millennial timescales in response to global climate events i e cooling during the last glacial maximum lgm heinrich event 1 h1 and the younger dryas yd and warming during the bolling allerod and in the early holocene during deposition of sapropel s1 the h1 cooling was particularly severe and is marked by a drop in sst of 4 5 c in comparison to pre h1 sst with temperatures 1 c cooler than during the lgm in contrast to high latitude and western mediterranean records which indicate both an abrupt onset and termination of the yd event the transition from the yd to the holocene was much more gradual in the em

unusual distributions of long chain alkenones and tetrahymanol from the highly alkaline lake van turkey long chain c37 to c40 alkenones with di tri and tetra unsaturation are very abundant in sediment trap material and holocene to late pleistocene core samples from the earth s largest soda lake lake van turkey thus the known distribution range of these typical biomarkers for haptophyte microalgae is extended to highly alkaline environments the observed unsaturation patterns differ strikingly from those found in open marine haptophytes and sediments by an enhanced relative abundance of the tetra unsaturated compounds especially the c37 4 methyl ketone their preponderance is suggested to be a facies marker pattern for lacustrine and marginal marine areas of sedimentation using published u37k calibrations no reliable absolute temperatures were obtained for the lake van samples accordingly marine sea surface temperature determinations based on long chain alkenones should be applied with caution when a contribution of these compounds from coastal or nonmarine sources can not be excluded the presence of tetrahymanol and gammacer 3 one in the lake van materials is attributed to organic matter contributions of ciliates the relative abundance of long chain alkenones and of tetrahymanol gammacer 3 one is considered to reflect changes in the environmental conditions in particular in the hydrological setting we suggest that times of pronounced stagnation are recognised by very high tetrahymanol gammacer 3 one concentrations together with drastically increased stanol stenol ratios and intervals of enhanced convection or of high freshwater input are characterised by high alkenone contributions

fossil pigments in paleoecology and paleolimnology abstract for the past several decades scientists have been examining the nature of sedimentary chlorophylls and carotenoids from freshwater lakes for their value in paleoecology and paleolimnology unaltered chlorophyll molecules are rarely preserved for long periods but the pheo derivatives and chlorophyllides are common throughout lake sedimentary columns carotenoids tend to preserve largely unaltered from their conditions in living plant membranes but degrade quickly to colorless derivatives when oxidized measurements of sedimentary pigment concentrations ratios of chlorophyll derivatives to carotenoids and diversity especially as regards prokaryote carotenoids are most commonly published this paper assesses the value of using sedimentary pigment data to provide paleoecological information on lake evolution and changing patterns of aquatic primary productivity factors that promote pigment preservation are contrasted to those that alter and cause destruction of organic molecules the value of fossil pigments is considered in ascertaining the sources of organic matter to sediments and for providing clues to the changing diversity of aquatic flora both rooted and planktonic consideration is given to recent investigations that have sought information from sedimentary pigments on the onset and intensity of cultural eutrophication both in individual lakes and on a regional basis and in the monitoring of progress toward lake restoration a special case is made for the value of sampling meromictic lakes in addition this review provides information on the limitations of the sampling procedures laboratory techniques and interpretation of results discussion is made of the most valuable and easily obtainable data that can provide reliable comparable and reproducible results special consideration is given to the value of the pigment data in supplementing additional paleoecological indicators such as sedimentary pollen grains zooplankton and various other sedimentary bio and geochemical products

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

comparison of lignin phenols and branched isoprenoid tetraethers bit index as indices of terrestrial organic matter in doubtful sound fiordland new zealand abstract the branched isoprenoid tetraether bit index has recently been proposed as a qualitative proxy for the relative amounts of soil and marine derived organic matter om in marine sediments we compare bit values with lignin phenol cuo oxidation products and bulk om proxies in surface sediment samples from doubtful sound a fjord in the southwestern end of new zealand s south island as well as in soils and leaf litter from the local pristine temperate rainforest watershed the region has extreme rates of annual rainfall 7 m year 1 and large mass wasting soil and vegetation events on fjord slopes which results in relatively high fluxes of terrestrial organic matter om terr to fjord sediments sediments contained up to 11 4 w w organic carbon oc with terrestrial to a mixture of terrestrial marine 13 c 24 3 to 28 7 and c n 14 7 36 8 signatures bit values ranged from 0 24 to 0 93 lignin abundance in sediments reported as 8 values mg 8 lignin phenols 100 mg oc 1 ranged from 2 7 to 11 2 a weak correlation was found between concentrations of lignin phenols and bit values r 2 0 313 the likely cause of the differences between the two proxies is differences in the relative amounts of soil om om soil and vegetation intact and detrital transported to the fjord by episodic mass wasting events and gradual accumulation from overland leaching by rainfall and riverine sources interestingly the bit index correlated significantly with bulk sedimentary om om sed proxies 13 c r 2 0 774 c n r 2 0 629 while lignin phenol values 8 exhibited a much weaker correlation with 13 c values r 2 0 320 and no correlation with c n values r 2 0 005 this suggests that om soil represents the dominant fraction of om terr delivered to fjord sediments

pronounced occurrence of long chain alkenones and dinosterol in a 25 000 year lipid molecular fossil record from lake titicaca south america abstract our analysis of lipid molecular fossils from a lake titicaca 16 s 69 w sediment core reveals distinct changes in the ecology of the lake over an 25 000 yr period spanning latest pleistocene to late holocene time previous investigations have shown that over this time period lake titicaca was subject to large changes in lake level in response to regional climatic variability our results indicate that lake algal populations were greatly affected by the changing physical and chemical conditions in lake titicaca hydrocarbons are characterized by a combination of odd numbered mid to long chain c 21 c 31 normal alkanes and alkenes during periods when lake level was higher latest pleistocene early holocene and late holocene the c 21 n alkane and the c 25 and c 27 alkenes dominate hydrocarbon distributions and indicate contribution from an algal source potentially the freshwater alga botryococcus braunii the c 30 4 methyl sterol dinosterol increases sharply during the mid holocene suggesting a greatly increased dinoflagellate presence at that time long chain alkenones lcas become significant during the early holocene and are highly abundant in mid holocene samples there are relatively few published records of lca detection in lake sediments but their occurrence is geographically widespread antarctica asia europe north america lake titicaca represents the first south american lake and the first low latitude lake in which lcas have been reported lca abundance and distribution may be related to the temperature dependent response of an unidentified algal precursor although the lca unsaturation indices cannot be used to determine absolute lake titicaca temperatures we suspect that the published lca u 37 k unsaturation calibrations can be applied to infer relative temperatures for early to mid holocene time when lca concentrations are high using these criteria the u 37 k unsaturation indices suggest relatively warmer temperatures in the mid holocene in contrast to previous speculation lipid analysis provides little evidence of a greatly increased presence of aquatic plants during the mid holocene instead it appears that a few algal species were dominant in the lake based on the dramatic rise in abundances of lcas and dinosterol during the early to mid holocene we suspect that the algal producers of these compounds rose in response to a combination of physical and chemical changes in the lake these include temperature salinity and alkalinity changes that occurred as lake level dropped sharply during a multi millennial drought affecting the central andean altiplano

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

wet phases in the sahara sahel region and human migration patterns in north africa the carbon isotopic composition of individual plant leaf waxes a proxy for c3 vs c4 vegetation in a marine sediment core collected from beneath the plume of sahara derived dust in northwest africa reveals three periods during the past 192 000 years when the central sahara sahel contained c3 plants likely trees indicating substantially wetter conditions than at present our data suggest that variability in the strength of atlantic meridional overturning circulation amoc is a main control on vegetation distribution in central north africa and we note expansions of c3 vegetation during the african humid period early holocene and within marine isotope stage mis 3 50 45 ka and mis 5 120 110 ka the wet periods within mis 3 and 5 coincide with major human migration events out of sub saharan africa our results thus suggest that changes in amoc influenced north african climate and at times contributed to amenable conditions in the central sahara sahel allowing humans to cross this otherwise inhospitable region

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

abrupt holocene climate change as an important factor for human migration in west greenland west greenland has had multiple episodes of human colonization and cultural transitions over the past 4 500 y however the explanations for these large scale human migrations are varied including climatic factors resistance to adaptation economic marginalization mercantile exploration and hostile neighborhood interactions evaluating the potential role of climate change is complicated by the lack of quantitative paleoclimate reconstructions near settlement areas and by the relative stability of holocene temperature derived from ice cores atop the greenland ice sheet here we present high resolution records of temperature over the past 5 600 y based on alkenone unsaturation in sediments of two lakes in west greenland we find that major temperature changes in the past 4 500 y occurred abruptly within decades and were coeval in timing with the archaeological records of settlement and abandonment of the saqqaq dorset and norse cultures which suggests that abrupt temperature changes profoundly impacted human civilization in the region temperature variations in west greenland display an antiphased relationship to temperature changes in ireland over centennial to millennial timescales resembling the interannual to multidecadal temperature seesaw associated with the north atlantic oscillation

co2 and temperature controlled altitudinal shifts of c4 and c3 dominated grasslands allow reconstruction of palaeoatmospheric pco2 abstract during the pleistocene the vegetation changes in the high colombian andes included changes from c3 to c4 plants this is inferred from 13c values of the c31 n alkane from the funza 2 sedimentary record taken from the high plain of bogota at 2550 m elevation the environmental factors thought to be responsible for these changes were investigated using a single point simulation of the biome3 vegetation model including changes in precipitation temperature and atmospheric co2 concentrations the model shows that changes are for a major part caused by these latter two factors the isotopic signature of the n alkanes of several extant c3 and c4 grasses from the area were determined to calibrate the interpretation of the isotopic record from the geochemical record we estimated the altitudinal distribution of c3 and c4 plants using present grass distribution patterns based on floristic data as a template this information in combination with palaeotemperature estimates enabled the reconstruction of atmospheric co2 concentrations the reconstructed co2 concentrations follow the trends of the vostok antarctic ice core through three glacial and two interglacial stages the lowest calculated co2 concentration is ca 210 ppmv for the glacial maxima and within the range of lowest values from vostok our highest value 310 ppmv is for interglacial mis 7 this represents a new method to reconstruct palaeoatmospheric pco2 it is less accurate than measurements from ice cores but has potential to be used for sediments that are much older than the ice cores

organic geochemical records of environmental variability in lake malawi during the last 700 years part i the tex86 temperature record abstract we have applied the tex86 paleothermometer to produce a surface water temperature record for lake malawi spanning the past 700 years over much of the record temperature fluctuates from 24 27 c with a mean of 25 c however there has been a substantial increase in temperature of 2 0 c during the past 100 years the tex86 temperature record reveals a strong similarity to the instrumental record both records demonstrate warming 0 7 1 4 c over the past 50 years as well as a cooling anomaly around 1959 comparison of the tex86 temperature record with the proxy records of primary productivity suggests that wind induced upwelling and or precipitation have a strong influence on the surface temperature of lake malawi

centennial scale compound specific hydrogen isotope record of pleistocene holocene climate transition from southern new england 1 northeastern north america experienced major climate shifts during the pleistocene holocene transition however there have been no high resolution isotopic records of climate change from this region here we present a centennial scale record of climate change during the transition based on d h ratios of behenic acid c22 nacid or ddba from a sediment core in blood pond massachusetts surface calibrations from a transect of 19 lakes in eastern north america show that ddba values track mean annual atmospheric temperature variations the abrupt climate events observed in blood pond records show remarkable similarity with greenland ice core d 18 o records during the pleistocene during the early holocene the northeastern north america ddba record was more variable than greenland possibly due to the close proximity of the laurentide ice sheet and impact of freshwater outbursts as the ice sheet rapidly retreated citation hou j y huang w w oswald d r foster and b shuman 2007 centennialscale compound specific hydrogen isotope record of pleistocene holocene climate transition from southern new england geophys res lett 34 l19706 doi 10 1029 2007gl030303

wet and arid phases in the southeast african tropics since the last glacial maximum plant leaf wax carbon isotopes provide a record of c 3 versus c 4 vegetation a sensitive indicator of aridity from the southeast african tropics since the last glacial maximum wet and arid phases in southeast africa were in phase with conditions in the global tropics from 23 to 11 ka but at the start of the holocene these relationships ended and an antiphase relationship prevailed the abrupt switch from in phase to out of phase conditions may partially be attributed to a southward displacement of the intertropical convergence zone itcz during the last glacial southward displacements of the itcz are also linked to arid conditions in southeast africa during the younger dryas and the little ice age

a comparison of biomarker records of northeast african vegetation from lacustrine and marine sediments ca 3 40 ma integrated terrestrial and marine records of northeast african vegetation are needed to provide long high resolution records of environmental variability with established links to specific terrestrial environments in this study we compare records of terrestrial vegetation preserved in marine sediments in the gulf of aden deep sea drilling project dsdp site 231 and an outcrop of lacustrine sediments in the turkana basin kenya part of the east african rift system we analyzed higher plant biomarkers in sediments from both deposits of known equivalent age corresponding to a ca 50 100 ka humid interval prior to the b tulu bor eruption ca 3 40 ma when the lokochot lake occupied part of the turkana basin molecular abundance distributions indicate that long chain n alkanoic acids in marine sediments are the most reliable proxy for terrestrial vegetation carbon preference index cpi 4 5 with more cautious interpretation needed for n alkanes and lacustrine archives marine sediments record carbon isotopic variability in terrestrial biomarkers of 2 3 roughly equivalent to 20 variability in the c3 c4 vegetation contribution the proportion of c4 vegetation apparently increased at times of low terrigenous dust input terrestrial sediments reveal much larger 2 10 shifts in n alkanoic acid d 13 c values however molecular abundance and isotopic composition suggest that microbial sources may also contribute fatty acids contaminating the lacustrine sedimentary record of terrestrial vegetation 2007 elsevier ltd all rights reserved

distribution and significance of long chain alkenones as salinity and temperature indicators in spanish saline lake sediments abstract we investigated relationships between sedimentary solvent extractable long chain alkenone lca concentration and composition and environmental factors in a suite of endorheic lakes from inland spain lcas were found in 14 of the 54 lakes examined with concentrations comparable with those from previously published lacustrine settings the composition of lcas in our sites however contrast from the majority of those previously reported from lake environments in our study the tri unsaturated component is the most abundant component at most sites where lcas are detected and c38 3 is the most abundant lca in the majority of sites lca occurrence appears to be restricted to brackish hypersaline sites and c37 lcas are absent above a salinity of 40 g l 1 suggesting a salinity control on lca producing organisms in these sites low concentrations of c37 lca components means u 37 k and u 37 k temperature indices are generally not applicable instead we find good relationships between c38 components and in particular mean autumn temperature and the strongest lca temperature relationships are found when using a combination of all c37 and c38 compounds we propose a new alkenone temperature index for lakes with elevated salinity and where the c38 components dominate the lca distributions this is expressed as u 3738 k 0 0464 mautat 0 867 r2 0 80 n 13 in this paper we provide the first account of sedimentary lca distributions from lakes in inland spain extending the range of environments within which these compounds have been found and highlighting their significance as indicators of both salinity and temperature in saline endorheic lake environments this has important implications for extending the potential role of lcas as palaeoclimatic indicators in lacustrine environments

diverse biohopanoid compositions of non marine sediments abstract biohopanoid compositions were determined for modern sediments from 27 lacustrine environments and 1 near coastal lagoon gc ms analysis of existing hopanols and those produced by a side chain cleavage reaction periodic acid and sodium borohydride of the bacteriohopanepolyols provided quantitative data for bacteriohopanetetrol bht bacteriohopanepentol and composite tetra penta and hexafunctionalised biohopanoids additional analysis of acetylated total extracts by hplc apci ms has allowed us to identify up to seven intact bacteriohopanepolyols in these environments including the first direct observation of 35 aminobacteriohopanepentol in environmental samples this method is complementary to the periodic acid approach in providing more specific compositional information the lacustrine environments exhibit a wide range of compositions many with high inputs of hexafunctionalised biohopanoids up to 60 of total tetra penta and hexafunctionalised biohopanoids indicative of major contributions to the sediment from type i methanotrophic bacteria several methylated biohopanoids were also detected in most of the samples with 2 as the dominant configuration of the methyl group 2 methylbacteriohopanetetrol was by far the most abundant and most commonly occurring compound of this type and comprised the most abundant bacteriohopanepolyol in one saline lake laguna grande spain such compounds are believed to be derived from cyanobacteria currently the only known quantitatively significant source of 2 methylated biohopanoids biohopanoids containing a methyl group at c 3 were also detected in a limited number of environments these data demonstrate the wide variability in bacteriohopanepolyol compositions among depositional environments and the potential of these compounds to preserve bacterial source information and thereby to record environmental change

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

determination of sediment provenance at drift sites using hydrogen isotopes and unsaturation ratios in alkenones the large 20 hydrogen isotopic gradient in surface waters of the northwest atlantic ocean is exploited to track changes in the source of alkenones to the bermuda rise sediment drift cultures of the predominant alkenone producing coccolithophorid e huxleyi were grown in deuterium enriched seawater and shown to possess alkenones with a d h ratio that closely tracked the water d h ratio r 2 0 999 n 5 isotopic enrichments with a fractionation factor between 0 732 and 0 775 a hydrogen isotopic depletion of 193 3 n 9 was measured in alkenones from suspended particles relative to seawater in the subpolar and subtropical northwest atlantic ocean this value was used to calculate the water d values in which alkenones from bermuda rise sediment were synthesized and by extension the water mass in which they were produced applying this technique we find that 60 to 100 of the alkenones in late holocene bermuda rise sediment were produced in deuterium depleted subpolar water to the northwest of the drift to reconcile values of the alkenone unsaturation ratio u k 37 a widely used proxy for sea surface temperature with the d values of alkenones in late holocene sediments from the bermuda rise at least three sources of sediment must be invoked a cold very isotopically depleted source almost certain to be the scotian margin a warm moderately isotopically depleted source likely to be the northwestern edge of the subtropical gyre and a cold isotopically enriched source which we hypothesize to be the subpolar waters overlying the main branch of north atlantic deep water flowing southwest from the nordic seas copyright 2005 elsevier ltd paleoclimate records with sufficient length and temporal resolution to study the occurrence and causal mechanisms of abrupt climate change are exceedingly rare rapidly deposited ocean sediments provide the best archive for studying these events through geologic time but such sites in the open ocean are limited to sediment drift deposits such as the bermuda rise in the northwest atlantic using multiple climate proxies in a single core is becoming more common in high resolution pa leoclimate investigations but a major potential concern for this approach arises from the possibility that the fine fraction of sediment e g 63 m and the climate proxies within it may represent conditions far from the deposition site here we propose and test the hypothesis that hydrogen isotope ratios of alkenones a class of lipids from phytoplankton may provide insight into the source of fine grained sediment because of their restricted sources broad geographic distri bution and excellent preservation properties alkenones are of particular interest in the emerging field of compound specific hydrogen isotopic analysis the sedimentary abundances ex tents of unsaturations and isotopic compositions of alkenones provide quantitative and near continuous records we isolated alkenones from cultured unicellular algae haptophyte emil iania huxleyi surface ocean particulate material and open ocean sediments to determine the extent and variability of hydrogen isotopic fractionation in the di tri and tetraunsat urated c37 compounds we then compared the d values of the alkenones in surface sediments between the bermuda rise and the scotian margin above which a large 20 d gradient exists we determined the fractionation between alkenones from suspended particulate samples and the water in which the phytoplanton lived and examined the variability of alkenone d values during the medieval warm period little ice age climate transition cf keigwin 1996 at the bermuda rise

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

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

paleovan international continental scientific drilling program icdp site survey results and perspectives lake van is the fourth largest terminal lake in the world volume 607 km 3 area 3570 km 2 maximum depth 460 m extending for 130 km wsw ene on the eastern anatolian high plateau turkey the sedimentary record of lake van partly laminated has the potential to obtain a long and continuous continental sequence that covers several glacial interglacial cycles ca 500 kyr therefore lake van is a key site within the international continental scientific drilling program icdp for the investigation of the quaternary climate evolution in the near east paleovan as preparation for an icdp drilling campaign a site survey was carried out during the past years we collected 50 seismic profiles with a total length of similar to 850 km to identify continuous undisturbed sedimentary sequences for potential icdp locations based on the seismic results we cored 10 different locations to water depths of up to 420 m multidisciplinary scientific work at positions of a proposed icdp drill site included measurements of magnetic susceptibility physical properties stable isotopes xrf scans and pollen and spores this core extends back to the last glacial maximum lgm a more extended record than all the other lake van cores obtained to date both coring and seismic data do not show any indication that the deepest part of the lake tatvan basin ahlat ridge was dry or almost dry during past times these results show potential for obtaining a continuous undisturbed long continental palaeoclimate record in addition this paper discusses the potential of paleovan to establish new results on the dynamics of lake level fluctuations noble gas concentration in pore water of the lake sediment history of volcanism and volcanic activities based on tephrostratigraphy and paleoseismic and earthquake activities c 2009 elsevier ltd all rights reserved

pigment preservation and remineralization in oxic coastal marine sediments abstract complex mixtures of sedimentary chlorophyll degradation products were measured using high performance liquid chromatography hplc in 210 pb dated box and piston core sediments sediments were collected from dabob bay washington a coastal marine fjord conducive to studies yielding an understanding of the remineralization and diagenesis of organic carbon greater than 99 of the pheopigment flux out of the water column does not accumulate in the top 2 cm of sediment surface sediment pigment profiles indicate that pheophorbides are the dominant pheopigments observed with concentrations decreasing rapidly with depth concentrations of chlorophyll c derivatives also decrease rapidly but ratios of a c pheopigments remain within ranges reported for natural and cultured phytoplankton sharp pheopigment concentration decreases within the bioturbated surface sediments as defined by 210 pb activities were modeled using a one dimensional mixing model the in situ pheopigment decomposition rate corrected for bioturbation and sediment accumulation corresponds to an approximate half life of 40 days sedimentary humic acid fulvic acid and residual humin associated pheopigments in sediments which had been previously acetone extracted to remove the lipophilic pheopigment fraction were typed by chromic acid oxidation and release of pyrrole derived maleimides this humic associated pyrrole derived nitrogen while a small fraction of total sedimentary or humic nitrogen accounted for 16 75 of the total sedimentary pheopigment accumulation and may be significant in understanding the diagenetic fate and transformation of pheopigments to petroporphyrins

glacial interglacial variations in carbon cycling revealed by molecular and isotope stratigraphy of lake nkunga mt kenya east africa abstract the lipid content n alkanes n alkanols n alkanoic acids and the 13c values of these lipids were measured in nineteen sediment samples taken from a 21 18 m long core from lake nkunga a high altitude 1820 m a s l freshwater lake situated in the montane rain forest on mt kenya the record spans the early last glacial marine isotope stages 5a to 4 and the late holocene 1030 45 14c yr bp to the present day the intervening hiatus spans the last glacial maximum and the early to mid holocene the molecular biogeochemical results are interpreted in terms of past changes in climate vegetation and atmospheric co2 concentration three different sources of organic matter input were identified from the n alkyl lipids namely terrestrial plants aquatic plants and algae unusual distribution patterns of dominant mid chain length n alkanes c23 25 n alkanols c22 24 and n alkanoic acids c22 24 are attributed to aquatic macrophytes an 11 decrease in bulk carbon isotope values between the sediments of early glacial 17 and late holocene age 28 is also apparent in the individual homologues of the n alkyl lipids the observed isotopic shift in terrestrial higher plant biomarkers is similar to that observed in nearby sacred lake and is consistent with an expansion of c4 grasses or sedges during the early glacial the corresponding vegetation was a dry montane juniper olive forest with a grassy understorey representing cold dry conditions with lower co2

prediction of impending failure of embankments on soft ground the deformation behaviour and excess pore pressure response of 13 well monitored embankments on soft ground that were constructed to failure have been analyzed the analysis shows that by monitorin

occurrence of novel monocyclic alkenes from diatoms in marine particulate matter and sediments abstract widely occurring alkenes reported in sediments from around the globe but which previously had unknown identities and sources have now been assigned they include a novel monocyclic c 25 triene and novel c 30 monocyclic tetra and pentaenes recently these compounds have been shown to be biosynthesised by some strains of the widespread planktonic diatom rhizosolenia setigera and this appears to be the likely source of the alkenes in the marine environment the hydrocarbons were identified by comparison of the gas chromatographic retention data and mass spectra of the sedimentary alkenes isolated from the arabian sea peru upwelling region and cariaco trench with data for the pure isolated alkenes from r setigera the compounds co occur with well known diatomaceous 7 20 highly branched isoprenoid haslenes and rhizenes in all of these environments but were absent from sediments from the black sea even though 5 haslenes were abundant in the latter sediments these differences possibly reflect the different diatom species contributing alkene lipids to each sedimentary environment the newly identified compounds may be further useful biological markers of diatom inputs to sediments

sedimentary pigments as markers for environmental change in an antarctic lake abstract fossil pigments were identified in a sediment core from kirisjes pond a small lake in the larsemann hills east antarctica using reversed phase hplc and lc ms ms chlorophyll a and b derived components indicate the presence of oxygenic primary producers steryl chlorin esters provide evidence of grazing while shifts in their esterifying sterol composition record changes in the primary producer community bacteriochlorophyll c and d derived components indicative of photic zone anoxia were identified with structural variations including extensive alkylation in the macrocycle up to c 6 the pigment distribution reveals a change from oxygenated freshwater to a stratified water body with development of photic zone anoxia this coincides with a marine incursion identified from diatom records and is followed by re isolation and reversion to oxygenated freshwater conditions

possible algal origin of long chain odd n alkanes in immature sediments as revealed by distributions and carbon isotope ratios a pliocene oil shale pula hungary a c3 plant triticum aestivum and a c4 plant zea mays were compared using isotopic composition of bulk organic matter along with distributions and individual carbon isotope ratios of n alkanes from organic extracts the microalga botryococcus braunii a race was thus shown to be the main source of the predominant 27 29 and 31 n alkanes of pula sediment therefore the dominance of odd carbon numbered n alkanes in the range c25 35 in extracts from immature sediments shall not be systematically assigned to higher plant contribution but algal input is also possible in fact the long chain n alkanes with an odd predominance previously observed in extracts of various immature sediments are likely to be derived at least partially from algae

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

inferring paleotemperature from the d h ratio of lacustrine organic matter abstract linking the d h d records of the kerogen from bulk organic matter in lake sediments to known temperature d of precipitation relationships may offer new possibilities in paleoclimate studies here we examine the hydrogen isotope ratio obtained from a radiocarbon dated lake core from wisconsin situated in the midwestern part of the united states to infer paleo surface temperatures paleotemperatures were estimated by converting the d values of the organic fraction to the d values of the lake water and by implication to that of local precipitation the temperature estimates show that the middle holocene from 7000 to 5000 years before present bp was warmer by about 3 c in general agreement with speleothem data from the midwestern united states our study shows the usefulness of the d h rations of kerogen from bulk sediment as a climate proxy that can compliment compound specific hydrogen isotope studies

compound specific radiocarbon dating of the varved holocene sedimentary record of saanich inlet canada 1 the radiocarbon contents of various biomarkers extracted from the varve counted sediments of saanich inlet canada were determined to assess their applicability for dating purposes calibrated ages obtained from the marine planktonic archaeal biomarker crenarchaeol compared favorably with varve count ages the same conclusion could be drawn for a more general archaeal biomarker gdgt 0 although this biomarker proved to be less reliable due to its less specific origin the results also lend support to earlier indications that marine crenarchaeota use dissolved inorganic carbon dic as their carbon source the average reservoir age offset r of 430 years determined using the crenarchaeol radiocarbon ages varied by 110 years this may be caused by natural variations in ocean atmosphere mixing or upwelling at the ne pacific coast but variability may also be due to an inconsistency in the marine calibration curve when used at sites with high reservoir ages

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

δd values of n alkanes in tibetan lake sediments and aquatic macrophytes a surface sediment study and application to a 16 ka record from lake koucha abstract a set of lake surface sediment samples and aquatic macrophytes from the eastern and central tibetan plateau and a sediment core from koucha lake northeastern tibetan plateau were analysed for hydrogen isotope signals of aliphatic lipid biomarkers the d values of n alkanes were correlated with those of meteoric water in the summer months and showed increasing pearson correlation coefficients with increasing n alkane chain length r 0 80 for n c 31 while in samples from the most humid regions southeastern tibetan plateau the apparent enrichment factors between meteoric water and lipids are close to those reported for other humid sites e 135 for mid chain and 125 for long chain n alkanes they become smaller e 118 to 41 mean value 86 at sites with a negative moisture balance northeastern and central tibetan plateau and qaidam basin this might be caused by enrichment in deuterium of the source water used for lipid synthesis as a result of lake water evaporation and soil and leaf water evapotranspiration in the core from lake koucha decreasing d values of all n alkanes between 15 and 10 cal ka bp give evidence for an intensification of the asian summer monsoon at ca 9 cal ka bp a ca 15 shift towards higher d values of mid chain n alkanes suggests enhanced evaporation of the lake water which outweighs higher precipitation amounts because of a temperature increase during the early holocene monsoonal maximum only a few surface sediment samples show a significant offset between d values of mid chain n alkanes and n c 31 d mid n c31 and no systematic dependence between this offset and environmental parameters such as mean annual precipitation was found in the core available data for most samples also do not show a significant offset only a slight increase 15 of d mid n c31 at ca 10 0 cal ka bp and a decrease 17 at ca 6 8 cal ka bp might indicate wetter and drier conditions respectively however interpretation of d mid n c31 throughout the record is difficult because of a lack of reliable data for n c 31 in key sections of the core so more records are necessary to further test the potential applicability of d mid n c31 as a proxy for palaeo hydrological conditions

lipid geochemistry of lake sediments from semi arid spain relationships with source inputs and environmental factors the lipid geochemistry of lake sediments can provide information on past environmental change detailed interpretation is however often hampered by a limited understanding of the provenance of many compounds and the multiple factors influencing their distributions in modern lake sediments we have quantified the solvent extractable lipid compositions of modern surface sediments from fifty four spanish lakes covering a range of hydrochemical fresh to hypersaline and hydrological shallow ephemeral to deep permanent conditions lipid compositions across the dataset are dominated by carboxylic acids up to 86 total solvent extractable lipids alkanols up to 63 and sterols up to 58 with smaller relative proportions of alkanes alkenes ketones including long chain alkenones and hopanols here we employ the distributions of these dominant compounds to explore relationships between lipid composition source inputs and lake type source input is the major factor influencing the lipid composition but there are also some indicators of early stages of lipid diagenesis in these surface sediments multivariate data analysis non metric multidimensional scaling ordination and cluster analysis of normalised lipid concentrations shows a distinction between compounds originating primarily from algal bacterial macrophyte or terrestrial plant sources this statistical technique enables sites to be grouped according to their dominant lipid compositional characteristics as well as enabling us to identify broad trends in groups of sites in terms of their environmental features e g shallow or deep lakes this modern training set study provides insight into patterns of contemporary lipid distributions and lipid source and site relationships across diverse lacustrine environments which can then be useful in environmental monitoring and palaeoenvironmental studies using sediment cores

variability of unusual distributions of alkenones in the surface waters of the nordic seas 1 samples of filtered particulate organic matter pom were obtained during the summers of 1999 and 2000 from the surface waters of the nordic seas to monitor the spatial distribution of long chain alkenones the aim of the study was to appraise existing alkenone based climatic proxies in northern high latitudes unusually high percentages of the tetraunsaturated alkenone were measured in the polar waters of the east greenland current with c37 4 of up to 77 in 80 of sea ice cover values of percent c37 4 across the nordic seas showed a strong association with water mass type analysis of coccoliths in filters indicated that calcified emiliania huxleyi could not be discounted as the biological precursor of alkenones in all the water masses a combined data set of 69 samples of pom revealed a stronger correlation of percent c37 4 to sea surface salinity sss r2 0 72 than to sea surface temperature sst r2 0 50 values of percent c37 4 in sea surface pom were much higher than those in surficial sediments of the northern north atlantic to explain the discrepancy in sedimentary and surface water column percent c37 4 we propose that the alkenone contents in surface sediments underlying arctic and polar waters are a combination of autochthonous and allochthonous inputs of alkenones our results show that percent c37 4 can be used to reconstruct the relative extension of arctic polar water masses in the north atlantic however the results prevent confirmation of percent c37 4 as a paleo sss proxy in the nordic seas given its multivariate nature in our data set and the decoupling between its range of values in surface waters and sediments

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

alkenone distributions in the north atlantic and nordic sea surface waters 1 the c37 c39 alkenones were quantified in suspended particulate matter obtained from the surface waters of the north atlantic including the nordic seas over a temperature range of 4 20 c u37k values were linearly correlated to temperature over the entire range covered by our data set i e 4 20 c u37k 0 027t 0 036 r2 0 97 the compilation of water column data from the atlantic pacific and southern ocean and mediterranean sea suggests that the linear model may not be the best function for fitting u37k and in situ temperature values it also shows that suspended matter data from warm waters t 20 c are still needed to constrain the equation of the global curve high abundances of c37 4 were found in the coldest polar waters around 4 c c37 4 represented up to 35 a value that dropped to zero at temperatures above 10 c values of c37 4 were linearly correlated to temperature c37 4 3 7t 43 7 r2 0 50 and salinity c37 4 48 1s 1691 r2 0 78 further investigations from other oceanic basins are necessary to confirm these findings

kerogen origin evolution and structure kerogen commonly defined as the insoluble macromolecular organic matter om dispersed in sedimentary rocks is by far the most abundant form of om on earth this fossil material is of prime importance as the source of oil and natural gas moreover kerogen can provide essential information on major topics such as past environments climates and biota this review reports the main advances in kerogen studies since the comprehensive synthesis edited by durand durand b ed kerogen insoluble organic matter from sedimentary rocks editions technip paris 1980 it is organized into eight sections the first two are concerned with the successive definitions of kerogen and the definition used here the different techniques used for kerogen isolation without loss or degradation and basic kerogen analysis the third and fourth focus on sedimentary om sources and preservation processes in relation to depositional environment including sedimentation conditions favourable for kerogen accumulation and extrapolation to past geological time great strides have been made in the latter topics over the last 25 years owing to a combination of classical studies in organic geochemistry and studies in other domains such as biogeochemistry oceanography hydrology and soil science along with the development of powerful analytical tools the next two sections deal with the different kerogen classifications by type and kerogen evolution and maturation upon burial in sediments structural modelling of coal and kerogen based on physical and or chemical structural analysis is described in the following section although only statistical the models thus derived provide a synthetic view of the main structural resemblances and differences among various samples in relation to source maturity or physicochemical properties finally the last section explores some of the advances in kerogen understanding expected for the near future the review includes a list containing about 500 references

decoupling of bio and geohopanoids in sediments of the benguela upwelling system bus abstract geohopanoids derive from bacteriohopanepolyol bhp precursors however knowledge of the specific sources and diagenetic fate of both compound classes in marine sediments is fragmentary we studied the relationship between bhps and geohopanoids in a sediment core from the central benguela upwelling system bus including deposits over the last 75 ka the bus is a palaeo oceanographically stable setting where primary production is largely controlled by variation in upwelling intensity and therefore nutrient supply marine production in the bus was generally higher during glacial than during interglacial times as reflected in the levels of sedimentary total organic carbon geohopanoids at the study site consisted mainly of extractable hopanes and hopanols and occurred in the highest amounts during glacial periods a minor but still considerable fraction of geohopanoids was sulfur linked to geomacromolecular organic matter among these s bound hopane moieties 17 h 21 h trishomohopane c33 was the predominant compound suggesting a diagenetic overprint of bhps before linkage among the bhps a rare bacteriohopanetetrol with likely 22s configuration was observed this structural feature was lacking in the geohopanoids which all had the 22r configuration different behaviour of bhp and geohopanoid concentrations as well as 13c discrepancies indicate a decoupling of bio and geohopanoids geohopanoids most likely reflect laterally transported fossil organic matter whereas bhps are indigenous to the upper water column of the study site and may relate to past upwelling intensity nutrient levels hence care has to be taken using geohopanoids and other biomarkers for palaeoreconstruction in settings where sedimentation processes are not fully understood

early diagenesis of bacteriohopanoids in recent sediments of lake pollen norway abstract the distribution of free bio and geohopanoids were studied in a short 46 cm core from recent sediments of lake pollen norway bacteriohopanepolyols are abundant components of the sediments totalling up to 321 g g dry sediment 7485 g g toc being dominated by c 32 33 34 35 tetrafunctionalised hopanoids significantly bacteriohopanetetrol only accounts for between 7 to 62 of these 24 on average indicating that composite bacteriohopanoids are more abundant sedimentary constituents and thus more important precursors of geohopanoids than previously recognised downcore profiles of bio and geohopanoid abundance show maxima at ca 25 to 30 cm with a marked decrease in abundance above this depth which coincides with a well documented change in environment from fjord to isolated lake a second maximum in biohopanoid abundance occurs at ca 5 to 12 cm depth specific biohopanoids were affected to different extents by the change in environment suggesting that they have at least partly different sources our data thus indicate that biohopanoids and their geohopanoid products may be sensitive to changes in depositional environment and that they have potential to act as markers for environmental conditions

rapid sulfurisation of highly branched isoprenoid hbi alkenes in sulfidic holocene sediments from ellis fjord antarctica samples of particulate organic matter from the water column and anoxic holocene sediment layers from the small meromictic basin smb in ellis fjord eastern antarctica were analyzed to study the early incorporation of reduced inorganic sulfur species into highly branched isoprenoid hbi alkenes hbis were not detected in the water column samples taken during austral winter whereas compounds containing the c25 hbi skeleton were abundant in all analyzed holocene sediment layers the structure of the c25 2 hbi alkene and its enriched stable carbon isotopic composition suggest that it is produced by a diatom or diatoms probably belonging to the navicula genus in the sea ice which covers the area most of the year within just 500 years of deposition all of the hbi alkene was sulfurised a mixture of products was formed including components tentatively identified as a c25 hbi thiane and three s containing dimers composed of two c25 1 hbi skeletons linked together by a sulfide bond most was however converted to polar s containing compounds the reaction rate for sulfurisation of the c25 2 hbi alkene is the highest observed so far in natural systems sterols and other lipids known to be prone to sulfurisation were not sulfurised the reason for this is unclear

δd values of individual n alkanes from terrestrial plants along a climatic gradient implications for the sedimentary biomarker record abstract the compound specific hydrogen isotope composition d of sedimentary n alkanes is increasingly used as a palaeoclimate proxy to explore the origin of the hydrogen isotope signal of n alkanes from higher terrestrial plant biomass in sedimentary organic matter of small lakes we have analysed the n alkane composition and d values of 31 plant biomass samples birch betula beech fagus oak quercus alder alnus hornbeam carpinus and myrtle myrtus as well as non stomata containing sphagnum cladonia and moss from 14 sites along a climatic gradient from northern finland to southern italy eleven of the sites were previously investigated for the n alkane d values in adjacent lake sediments and are compared to the leaf wax n alkane d values the distribution of terrestrial n alkanes in lake sediments was not found to be characteristic of the dominant vegetation around the lake evidently n alkane distributions within the same species at different sites were found to be variable these findings complicate the use of certain n alkane distributions in sediments as a palaeoenvironmental indicator d values of plant biomass n alkanes show a significant positive correlation with the precipitation d values biomass n alkane d values are in general less negative than the associated sedimentary n alkanes of terrestrial origin possibly due to the stronger evapotranspiration during the summer when sampling took place this suggests that n alkanes in leaves show seasonal variations and the sedimentary organic matter receives the lighter isotope signal of the autumn when most leaves are incorporated into the sediment the variability of the d values from non stomata containing plants is much higher than for broadleaf trees since stomata can regulate water loss through evapotranspiration the average chain length acl of n alkanes from deciduous tree leaves increases from north to south with increasing acl the hydrogen isotopic fractionation e between source water and n alkanes also increases our results prove that terrestrial n alkane d values record the d value of precipitation modified by the amount of isotope enrichment in the leaf water due to plant anatomy stomata vs no stomata and site specific meteorological conditions such as evapotranspiration relative humidity and soil moisture therefore terrestrial n alkanes in lake sediments can deliver information on changes in these parameters over geological timescales in lake sediments where aquatic n alkanes such as n c 17 record the lake water d value the isotopic difference between terrestrial and aquatic n alkanes could therefore be used to reconstruct changes in evapotranspiration

occurrence of long chain n alkenols diols keto ols and sec alkanols in a sediment core from a hypereutrophic freshwater lake abstract long chain mid chain diols and keto ols have been reported mainly in marine environments but only rarely in lacustrine sediments in this work exceptionally high abundances and diversity of keto ols diols and structurally related long chain n alkenols and secondary alkanols were detected in sediments from a hypereutrophic freshwater lake lake valencia venezuela the maximum concentrations are 241 g g toc for n alkenols 75 g g toc for diols 367 g g toc for keto ols and 8 7 g g toc for secondary alkanols eleven keto ol isomers were identified which is the highest diversity yet reported for sediments the presence of five keto ol isomers namely 1 12 c 30 keto ol 1 14 c 31 keto ol 1 15 c 33 keto ol 1 16 c 33 keto ol and 1 18 c 35 keto ol is reported for the first time the mass spectra for osmium tetroxide derivatives from long chain n alkenols confirmed the double bond location at carbons 13 14 or 15 the carbon isotope compositions were substantially enriched in 13 c for n alkenols diols and keto ols 13 c 22 0 2 2 relative to the corresponding long chain n alkanols 29 6 0 8 suggesting an autochthonous aquatic microbial origin rather than from a terrestrial i e fern source although a strong predominance of cyanobacteria was reported for in the lake s plankton community 90 and relatively low abundance of sedimentary sterols suggests cyanobacteria as a potential source eustigmatophytes a major reported producer of diols and keto ols cannot be excluded because eustigmatophytes are easily confused with other microalgae and may have been overlooked in previous studies n alkenols and keto ols displayed similar historical patterns over the past 10 000 years but there were distinct differences from the diol patterns this result suggested that n alkenols and keto ols may be derived from the same sources while diols either undergo different environmental diagenesis or have different sources a keto ol index coincides well with the hydrological changes of lake valencia over the last 10 000 years and corroborates its validity as a paleo indicator

carotenoid diagenesis in recent marine sediments ii degradation of fucoxanthin to loliolide abstract the quantitative distributions of loliolide and the major phytoplankton carotenoids fucoxanthin diadinochrome diatoxanthin and carotene in two cores of anoxic marine sediment recovered from the peru continental shelf are reported our results demonstrate that the rapid degradation of carotenoids in sediments is not a result of their high degree of unsaturation as has been previously suggested instead carotenoids exhibit a wide range of degradation rates that are proportional to the ability of specific pigments to form unstable bicyclic furanoxides carotenoid furanoxides undergo subsequent fragmentation to loliolide isololiolide dihydroactinidiolide and other as yet undetermined low molecular weight products this degradation pathway accounts for the relative rates of removal for specific carotenoids fucoxanthin fucoxanthinol diadinoxanthin diatoxanthin carotene the distribution of carotenoids reported by wpatts and maxwell 1977 and c ardoso et al 1978 in ancient sediments the occurrence of novel carotenoid transformation products in surface sediments reported by r pidout et al 1984 and the distribution of loliolides in recent sediments recovered from the namibian shelf reported by k plok et al 1984a b we predict that loliolide and isololiolide will inherit a specific stereochemistry from their carotenoid precursors but that dihydroactinidiolide will be racemic for every mole of fucoxanthin degraded in peru sediments 0 7 1 1 mole of loliolide is produced summation of fucoxanthin and loliolide at each subsurface horizon yields an estimate of the total deposition of fucoxanthin at t 0 throughout the 0 20 cm depth of our samples this parameter is remarkably constant to 16 individual horizons exhibit excursions which may reflect changes in surface productivity extrapolation of our measurements to deeper sediments may therefore be of some value in deciphering questions on environmental conditions of deposition and paleoproductivity

spatial and temporal offsets between proxy records in a sediment drift chronologies for late quaternary marine sediment records are usually based on radiocarbon ages of planktonic foraminifera signals carried by other sedimentary components measured in parallel can provide complementary paleoclimate information a key premise is that microfossils and other indicators within a given sediment horizon are of equal age we show here that haptophyte derived alkenones isolated from bermuda rise drift sediments are up to 7000 years older than coexisting planktonic foraminifera this temporal offset which is apparently due to lateral transport of alkenones on fine grained particles from the nova scotian margin markedly influences molecular estimates of sea surface temperatures more broadly the observation raises questions about both the temporal and the geographic fidelity of paleoenvironmental records encoded by readily transported components of sediments

well preserved palaeogene and cretaceous biomarkers from the kilwa area tanzania we have investigated the biomarker composition of sediments ranging in age from 30 to 70 ma from the kilwa area of tanzania they are dominated by material of terrestrial n alkanols n alkanoic acids n alkanes and triterpenoids and bacterial hopanoids and a dipentadecyl glycerol diether dgd origin with only a minor contribution of marine origin crenarchaeol and some algal steroids this indicates a marine setting dominated by higher plant input which most likely stimulated sedimentary microbial activity including sulfate reduction the lipid composition specifically the presence of bacteriohopanepolyols bhps and the stereochemistry of hopanoids suggests a low degree of thermal maturity many biomarkers have still retained functionality even after 30 70 million years this is in good agreement with the exceptional preservation of foraminifera and nannofossils and can probably be attributed to the very low sediment permeability and burial depth there is a clear distinction in the biomarker distributions between the oligocene age sediments collected at the end of the peninsula near kilwa masoko and the older sediments collected from elsewhere indicating differences in depositional environment sediments from the end of the peninsula have higher branched and isoprenoid tetraether index values indicating a relatively higher terrestrial input they also contain two tentatively assigned c28 hopenes 28 30 dinorneohop 13 18 ene and 28 30 dinorhop 17 21 ene aromatic des a triterpenes des e hopenes aromatic pentacyclic triterpenoids c33 dgd archaeol and bhps which are absent from or only present in small amounts in the other sediments these differences likely reflect an evolution of the depositional area from a relative open shelf environment with substantial water depth to a shallower setting during the early oligocene

coupled thermal and hydrological evolution of tropical africa over the last deglaciation we analyzed the distribution of branched tetraether membrane lipids derived from soil bacteria in a marine sediment record that was recovered close to the congo river outflow and the results enabled us to reconstruct large scale continental temperature changes in tropical africa that span the past 25 000 years tropical african temperatures gradually increased from 21 to 25 c over the last deglaciation which is a larger warming than estimated for the tropical atlantic ocean a direct comparison with sea surface temperature estimates from the same core revealed that the land sea temperature difference was through the thermal pressure gradient an important control on central african precipitation patterns

bacteriohopanepolyols as tracers for continental and marine organic matter supply and phases of enhanced nitrogen cycling on the late quaternary congo deep sea fan abstract few studies have successfully identified bacteriohopanepolyols bhps in continuous sedimentary records older than 100 ka here we expand significantly on previous work and report high resolution records of a variety of fully functionalised bhps from odp site 1075 in the congo deep sea fan bhps are present throughout the core in sediments up to ca 1 2 ma including composite and unsaturated homologues although adenosylhopane a proposed tracer for soil organic matter input seems to undergo significant diagenesis with increasing depth below 65 m below the sea floor mbsf most bhps appear to be relatively resilient to degradation highlighting their potential as sedimentary tracers for past bacterial population distributions an unusual unsaturated bht cyclitol ether is present in high concentration between 500 and 600 ka and is interpreted as a possible biomarker for nitrogen fixing trichodesmium cyanobacteria this previously unrecognised ecosystem change may have been partially driven by a decrease in nutrient supply to surface waters resulting in more intense pelagic n fixation

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

comparison of ladderane phospholipid and core lipids as indicators for anaerobic ammonium oxidation anammox in marine sediments abstract we investigated anaerobic ammonium oxidation anammox in continental shelf and slope sediments of the irish and celtic seas by using anammox specific ladderane biomarker lipids we used the presence of an intact ladderane phospholipid as a direct indicator for living anammox bacteria and compared it with the abundance of ladderane core lipids derived from both living and dead bacterial biomass all investigated sediments contained ladderane core lipids as well as the intact ladderane phospholipid in agreement with 15 n labeling experiments which revealed anammox activity at all sites ladderane core lipid and intact ladderane phospholipid concentrations were significantly correlated r 2 0 957 and 0 464 respectively with anammox activity over the transect of the continental shelf and slope sediments in the irish sea 50 100 m water depth highest abundances of the intact ladderane phospholipid were found in the upper 2 cm of the sediment indicating a zone of active anammox a sharp decline further down core suggested a strong decrease in anammox biomass and rapid degradation of the intact lipids in comparison ladderane core lipids were 1 2 orders of magnitude higher in concentration than the intact ladderane phospholipid and accumulated as dead cell remnants with depth in the slope sediments of the celtic sea both ladderane core lipids and the intact ladderane phospholipid were found in sediments at water depths ranging from 500 to 2000 m here anammox seemed to be active at greater depths of the sediment 2 cm mean abundances of both intact and core ladderane lipids in whole sediment cores increased downslope indicating an increasing importance of anammox in deeper slope sediments

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

environmental influence on the biohopanoid composition of recent sediments abstract bacteriohopanepolyols are the biological precursors of extended hopane biomarkers which are ubiquitous in the geosphere the abundance and composition of these biohopanoids were determined for modern sediments from eight depositional environments by gc ms analysis of hopanols derived from a side chain cleavage reaction periodic acid and sodium borohydride of the bacteriohopanepolyols we report quantitative data for bacteriohopanetetrol bht composite tetrafunctionalised biohopanoids pentafunctionalised biohopanoids and hexafunctionalised biohopanoids bht was found in concentrations higher than previously reported up to ca 1500 g g toc but comprised only a relatively small proportion 0 26 of the total biohopanoids in all except one sample composite tetrafunctionalised biohopanoids were the dominant group of bacteriohopanepolyols in all other sediments and are likely to be a major source of the geologically occurring extended hopanes hexafunctionalised biohopanoids were most abundant in lake sediments particularly two small highly productive stratified lakes where they comprised 20 40 of total biohopanoids this feature is interpreted to be due to greater contribution to the organic matter of these sediments from type i methanotrophic bacteria which produce dominantly hexafunctionalised biohopanoids consistent with the environmental settings in the marine environments where sulphate reduction is dominant hexafunctionalised biohopanoids are relatively minor constituents 2 6 of total biohopanoids these data comprise the first clear demonstration that bacteriohopanepolyols vary in composition between depositional environments and have the potential to preserve specific bacterial source information in sedimentary organic matter

identification of aryl isoprenoids in source rocks and crude oils biological markers for the green sulphur bacteria abstract a series of c13 to c31 aryl isoprenoids 1 alkyl 2 3 6 trimethylbenzenes have been identified in reef hosted oils and their source rocks from the middle and upper silurian of the michigan basin and middle devonian of the alberta basin canada their structure has been confirmed by unambiguous synthesis of the c14 member of the series their structure and isotopic composition indicate that they are derived from isorenieratene from the chlorobiaceae family of sulphur bacteria these results are consistent with geological and geochemical studies that show that the source rocks were deposited under metahaline to hypersaline sulphate and sulphide rich water columns the distribution of other biomarkers in these oils and source rocks indicates that a diverse biota contributed organic matter to the source environment in conjunction with the aryl isoprenoids they show that there is a remarkable similarity in composition between the two sets of oils and source rocks despite their great temporal and geographic separation this reflects the similarity of their environments and emphasizes the importance of sedimentary facies in controlling the composition of organic matter in source rocks and their derived oils

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

an experimental field study to test the stability of lipids used for the tex86 and uk 37 palaeothermometers abstract we report a one year field experiment to study sedimentary degradation of isoprenoid glycerol dialkyl glycerol tetraethers gdgts and long chain alkenones lipids used for the tex86 and u 37 k sea surface temperature sst proxies respectively homogenised surface sediments from the namibian upwelling region were set out on moorings in oxic oder bay and arkona bay baltic sea and sub oxic to anoxic gottland basin baltic sea waters and in oxic atlantic waters off cape blanc for one year to assess the influence of oxygen exposure on gdgts and alkenones no selective degradation effect on both tex86 and u 37 k proxies was evident under anoxic and sub oxic conditions under oxic conditions gdgt concentrations and the tex86 did not significantly change as well however selective degradation of alkenones occurred at all oxic sites resulting in a small but significant increase of the u 37 k index by up to 0 06 units corresponding to a temperature increase of up to 1 8 c our results demonstrate that selective alkenone degradation is a relatively fast process and complement earlier evidence for selective degradation of alkenones in the laboratory water column and sediments in contrast our results suggest that the tex86 is relatively resistant to selective oxic degradation at least on relatively short years time scales

late miocene atmospheric co2 concentrations and the expansion of c4 grasses the global expansion of c4 grasslands in the late miocene has been attributed to a large scale decrease in atmospheric carbon dioxide co2 concentrations this triggering mechanism is controversial in part because of a lack of direct evidence for change in the partial pressure of co2 pco2 and because other factors are also important determinants in controlling plant type distributions alkenone based pco2 estimates for the late miocene indicate that pco2 increased from 14 to 9 million years ago and stabilized at preindustrial values by 9 million years ago the estimates presented here provide no evidence for major changes in pco2 during the late miocene thus c4 plant expansion was likely driven by additional factors possibly a tectonically related episode of enhanced low latitude aridity or changes in seasonal precipitation patterns on a global scale or both

a study of the alkenone tex86 and planktonic foraminifera in the benguela upwelling system implications for past sea surface temperature estimates suspended particulate matter from seawater and core top sediments were collected during 2003 meteor cruise m57 1 in january february from the continental margin off western south africa for analysis of alkenones glycerol dibiphytanyl glycerol tetraether gdgt lipids and planktonic foraminifera alkenone analysis of suspended particulates in seawater and core top sediments indicates that u37k temperatures were representative of annual mean sea surface temperature in contrast gdgt analysis suggests that tex86 temperatures are cold biased due to upward transports of gdgts produced below the mixed layer the analysis of plankton tow samples revealed that the 18o of globorotalia inflata in core top sediments could be biased toward lower temperatures due to subsurface calcification accordingly our study shows that each paleotemperature proxy may record different temperature signals in the benguela upwelling system emphasizing the general need to constrain potential biases in each proxy for better interpreting paleoclimate records

alkenone producers inferred from well preserved 18s rdna in greenland lake sediments 1 the 18s ribosomal dna rdna sequences of haptophyte algae were successfully amplified using the polymerase chain reaction pcr from water filtrate surface sediments and a late holocene sediment sample 1000 years old from a group of lakes in the sondre stromfjord region of west greenland the dna of the algal primary producer is extremely well preserved in the laminated lake sediments which have been deposited in cold 1 2c anoxic and sulphidic bottom water phylogenetic analyses of the greenland haptophyte rdna sequences suggest that alkenones in the greenland lake sediments are produced by haptophyte algae of the class prymnesiophyceae the 18s rdna sequences from the greenland samples cluster within a distinct phylotype differing from both marine haptophytes and from those reported previously from ace lake antarctica the similarity of haptophyte rdna sequences among all samples in this study suggests a single alkenone based temperature calibration may be applied to these lakes for at least the past 1000 years these sedimentary archives hold great promise for highresolution alkenone based paleotemperature reconstruction of southern west greenland a region sensitive to atmospheric oceanic climate phenomena such as the north atlantic oscillation nao

a study of the tex86 paleothermometer in the water column and sediments of the santa barbara basin california 1 particulate organic matter collected during a 2 year period as part of an ongoing sediment trap study and a high resolution sediment record from 1850 to 1987 a d from the santa barbara basin were analyzed for tex86 a temperature proxy based on marine crenarchaeotal membrane lipids highest fluxes of crenarchaeotal lipids in the water column were found in may june 1996 and from october 1996 to january 1997 and in general showed a good correlation with mass fluxes tex86 reconstructed temperatures from the sediment trap series ranged from 8 to 11 c and were usually substantially lower than sea surface temperatures sst indicating that unlike in previous studies the tex86 corresponds to subsurface temperatures likely between 100 and 150 m tex86 temperature variations observed in trap samples were not coupled to changes in sst or deep water temperatures and only to some degree with crenarchaeotal lipid fluxes this suggests that a complex combination of different depth origins and seasonal growth periods of crenarchaeota contributed to the variations in tex86 signal during the annual cycle tex86 temperatures in the two sediment cores studied 8 13 c were also substantially lower than those of instrumental sst records 14 17 5 c confirming that tex86 records a subsurface temperature signal in the santa barbara basin this result highlights the importance of performing calibration studies using sediment traps and core tops before applying the tex86 temperature proxy in a given study area

late quaternary glaciation and postglacial stratigraphy of the northern pacific margin of canada abstract areas of southeastern alaska and the queen charlotte islands of the northwestern pacific coast of north america were considered to be ice free during the late wisconsinan glaciation and glacial refugia existed however a glacier extended from mainland north america to the shelfbreak in dixon entrance separating alaska and the queen charlotte islands glacial retreat to the east began sometime after 15 000 to 16 000 14 c yr b p and ice had completely left dixon entrance by 13 500 to 13 000 14 c yr b p a rapid sea level regression occurred soon after deglaciation began due to isostatic rebound with relative sea level falling to approximately 150 m below present in central dixon entrance decreasing the size of the inlet by about 30 percent by 12 400 14 c yr b p the late quaternary glacial and postglacial stratigraphic sequence is more than 100 m thick overlying older pleistocene sediments and tertiary bedrock a late wisconsinan diamicton is overlain by glaciomarine muds formed between approximately 14 400 and 13 000 14 c yr b p contemporaneous with the deposition of the glaciomarine muds an extensive outwash deposit formed off the northern coast of the queen charlotte islands to a present depth of 150 m during the sea level lowstand and subsequent transgression a reworked sand unit was deposited over much of the seafloor to depths greater than 450 m the unit is exposed at the seafloor over much of the region suggesting that seabed hydrodynamic energy levels were high after 13 000 14 c yr b p and remain so today

simulation of co2 concentrations temperature and stratification in lake nyos for different degassing scenarios 1 a large gas cloud erupted unexpectedly in 1986 from lake nyos the larger of the two cameroonian killer lakes with devastating consequences regular monitoring subsequently revealed that the deep water of the lake was gradually recharged with co2 to preclude a similar event in the future a degassing pipe was installed in the lake in 2001 in the present study a one dimensional model is used to predict the effects of this pipe and other degassing options on the co2 concentrations and the stratification within the lake for the next 50 years the results of the simulations show that without degassing total co2 content would reach the preeruption value within a few decades the presently installed pipe is sufficient to reduce co2 pressures in the entire water column above the pipe inlet to 5 bar within 10 years and a steady state is reached within 50 years depending on the assessment of the risk due to the gas currently remaining in the lake and the costs involved the installation of additional pipes could be considered 1 to remove the gas more quickly and 2 as a backup for long term failures and maintenance once the steady state is reached degassing with one pipe is a practicable long term solution which can also be used for monitoring the approximate deep water co2 concentrations by nonprofessionals assuming a doubled deep water input in the future as an upper limit of the expected source strength the pipe is still able to prevent a co2 accumulation as a side effect the degassing operation strongly changes the stratification in the lake it transforms the lake from a meromictic to an oligomictic system and gradually removes the dissolved salts from the lake

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

tracking soil organic carbon transport to continental margin sediments using soil specific hopanoid biomarkers a case study from the congo fan odp site 1075 the transport and deposition of terrestrially derived organic matter tom into the ocean is an important but poorly constrained aspect of the modern global carbon cycle a preliminary study of late quaternary sediments from the congo deep sea fan odp leg 175 site 1075 2 km water depth and four surface samples from associated cores has confirmed the presence of proposed soil specific bacteriohopanepolyol biomarkers bhps including adenosylhopane in samples to a depth of 89 m concentrations of soil marker bhps are high in the upper sediment section to 49 m and the closest related surface sample 4913 supporting the case for these molecular markers as novel proxies for soil organic carbon soc supply via riverine transport and subsequent burial distinct peaks for the markers at about 21 34 and 60 m below surface level tentatively imply that the rate of tom discharge from tropical africa significantly increased at these times possibly associated with periods of reduced soil stability in the congo catchment

occurrence and abundance of soil specific bacterial membrane lipid markers in the tet watershed southern france soil specific bhps and branched gdgts recently four bacteriohopanepolyols bhps adenosylhopane and structurally similar adenosylhopane type 1 2 methyl adenosylhopane and 2 methyl adenosylhopane type 1 have been suggested to be characteristic of soil microbial communities and therefore can serve as molecular markers for soil organic matter om supply in river lake and marine sediments in this study we analyzed bhps in peats and soils collected in the tet watershed southern france and compared them with branched glycerol dialkyl glycerol tetraethers gdgts a more established molecular tracer of soil om adenosylhopane type i is identified in all of the samples from the study area except one collected near the tet river mouth with up to three of the related compounds also frequently present particularly in the surface samples the concentrations of soil specific bhps in peat environments have been shown to increase with lower delta 15 n values providing evidence that n 2 fixing bacteria are probably a major source of soil specific bhps in acidic environments it seems likely that soil ph is a major factor controlling bhp occurrence based on statistical analysis of environmental parameters and bhp concentration data the comparison of the soil specific bhp concentrations with those of branched gdgts shows no clear relationship in the tet river system supporting the concept that these two groups of soil specific compounds are synthesized by different microbial organisms living in different niches in the soil profile e g oxic top versus anoxic deep

the biomarker record of lake albano central italy implications for holocene aquatic system response to environmental change abstract a study of lipid biomarkers in predominantly laminated organic carbon rich sediments in lake albano central italy has been used to reconstruct changes in the aquatic system variations and changes in the lake catchment area during the holocene biomarkers of aquatic organic matter such as dinosterol isoarborinol tetrahymanol diplopterol and diploptene reflect two major changes in the mixing behaviour and the biological assemblages of lake albano at around 6 5 and 3 8 ky bp respectively biomarkers for higher land plants such as friedelin long chain n alkanes amyrenone and amyrenone display different distribution patterns indicating changes in the lake s catchment at 6 5 and 5 0 ky bp resulting from soil erosion and changes in the local vegetation analogously the recognised changes in the water column structure and biological components are coherent with previous reconstructions based on independent parameters the new data highlight the importance of multiproxy studies to better characterize palaeoenvironmental changes that are in turn the first step towards elucidating their trigger mechanisms i e climate vs human induced

a radiocarbon based assessment of the preservation characteristics of crenarchaeol and alkenones from continental margin sediments crenarchaeotal glycerol dibiphytanyl glycerol tetraether gdgt lipids and alkenones are two types of biomarkers derived from planktonic marine microorganisms which are used for reconstruction of sea surface temperature we determined the radiocarbon contents of the archaeal gdgt crenarchaeol and of alkenones isolated from continental margin sediments systematic differences were found between the two biomarkers with higher radiocarbon content in crenarchaeol than in the phytoplankton derived alkenones these differences can be explained by variable contributions of pre aged laterally advected material to the core sites crenarchaeol appears to be more efficiently degraded during transport in oxygen replete environments than alkenones whether this reflects the influence of chemical structure or mode of protection e g particle association is not known

stable isotope paleoclimate records for southern ontario canada comparison of results from marl and wood profiles of 18o in two marl cores from southern ontario canada are compared in detail with the records of meteoric water isotopic composition and photosynthetic humidity obtained from previous isotopic studies using wood cellulose at brampton ontario by accounting for the inferred changes in meteoric water composition and temperature the changes in the oxygen isotope content of the marl arising from fluctuations in the evaporative enrichment of the lakewater can be estimated the resulting synthetic profiles of relative evaporative enrichment from both marl cores exhibit strong correspondence to the photosynthetic humidity profile generated from the studies at brampton which substantiates the importance of evaporation in the water budgets of these two lakes a striking analogy exists between the isotopic evaporative enrichment response of such lakewaters and that of the waters in terrestrial plants both of the marl lakes approach close to isotopic steady state during the summer season when carbon

interhemispheric appraisal of the value of alkenone indices as temperature and salinity proxies in high latitude locations alkenone sediment data from the nordic seas and north atlantic are compared to those from sikes et al 1997 for the southern ocean to evaluate further uk37 and uk37 as proxies to estimate cold temperatures 10 c and the effect of salinity and temperature in the relative abundance of 37 4 to the total abundance of c37 alkenones 37 4 uk37 and uk37 are found to be equally viable as proxies but there are significant regional differences in their cold temperature dependence the measurement of 37 4 in cores from the north atlantic region can be used to identify situations when uk37 is not a reliable paleothermometer variations in salinity are probably responsible for changes in the sedimentary record of 37 4 and a preliminary calibration has been obtained for 37 4 f salinity this new relationship should be further confirmed through field or laboratory experiments but it paves the way to derive a molecular proxy to reconstruct paleosalinity in surface waters