ring index a new strategy to evaluate the integrity of tex86 paleothermometry the tex86 tetraether index of 86 carbon atoms sea surface temperature proxy has been increasingly applied in the reconstruction of mesozoic and cenozoic ocean temperatures however the archaeal lipids that compose tex86 indices glycerol dialkyl glycerol tetraethers gdgts can derive from water column production terrestrial sources and or within sediments tex86 sea surface temperature estimates can also be influenced by non temperature factors such as growth phase and nutrient levels here we show that the weighted average of cyclopentane moieties known as the ring index ri can be used to determine if tex86 temperature estimates are influenced by non thermal factors and or deviate from modern analogues we demonstrate that ri and tex86 indices from the published global core top data set and mesocosm cultures are significantly correlated as predicted through the influence of temperature on lipid biochemistry we further show that when ri and tex86 indices in modern or ancient records deviate from the modern global tex86 ri relationship gdgt distributions are not solely controlled by environmental temperature and or tex86 based temperature reconstructions are questionable

long chain alkenones and alkyl alkenoates as palaeotemperature indicators their production flux and early sedimentary diagenesis in the eastern north atlantic the production and fate of long chain alkenones and alkenoates was examined with regard to their use as palaeotemperature indicators alkenoate abundances were higher than previously reported for other regions and more strongly correlated with temperature than was alkenone unsaturation u37k suggesting biogeographical variability in alkenone and alkenoate production in surface waters we define the aa36 ratio to parameterize alkenoate abundance and present an empirical temperature calibration derived from our euphotic zone samples for use in the north atlantic t 17 35 25 12 u37k 26 73 aa36 93 90 u37k aa36 significant diagenetic losses of alkenones and alkenoates were found within the water column and near surface sediments in spite of diagenetic losses the temperature signal recorded by these compounds in the sediments remains largely unaltered and corresponds to the euphotic zone water temperature during the springtime period of maximum coccolithophorid production and flux rather than the average annual sea surface temperature

variability in upwelling intensity and nutrient regime in the coastal upwelling system offshore namibia results from sediment archives the coastal upwelling system offshore namibia is ideally suited to address a focal question of the integrated marine biogeochemistry and ecosystem research programme what are the mechanisms that drive long term changes in ecosystems considerable interannual variability in climatic forcing is indicated by long time series of meteorological and remote sensing observation these accompany considerable interannual to interdecadal changes in the upwelling intensity over the last 100 years as well as a centennial trend on longer time scales the only archives available are sediment records spanning the late holocene to decipher the sediment record we mapped surface sediment patterns of proxies for physical sea surface temperature sst from alkenone unsaturation indexes and nutrient 15n on bulk sedimentary n variables their present day surface sediment patterns outline the coastal upwelling cells and filaments and associated high productivity area analysed in an array of dated sediment cores the spatial patterns of sst suggest long term 100 years variability in the location and intensity of individual upwelling cells the patterns of 15n outline an area of intense denitrification near the coast and advection of water with low oxygen concentrations in the undercurrent from the north 15n exhibits considerable downcore variability in particular over the last 50 years the variability appears to be governed by differences in extent of denitrification and thus of the shelf oxygen balance which appears to have deteriorated in the last 50 years together the data suggest that sst and denitrification conditions have remained in the narrow bounds outlined by today s patterns in surface sediments but that spatially small variability in upwelling intensity and make up of upwelling feed waters induced considerable changes in the lower trophic levels of the coastal upwelling ecosystem over the last 6 000 years attempts to correlate proxy records from sediments with observational time series and regional climate reconstructions were not successful possibly because annual to interannual environmental signals are erased in the process of sediment formation

reconstruction of sea surface temperature variations in the arabian sea over the last 23 kyr using organic proxies tex86 and u37k well established u37 0 based on long chain unsaturated ketones synthesized by haptophyte algae and the newly proposed tex86 derived from the membrane lipids of crenarchaeota comparison of niop905 and 74kl core top data with present day sst 0 10 m values indicates that both proxies yield temperatures similar to local annual mean ssts however tex86 and u37 0 sst down core records derived from the same cores differ in magnitude and phasing the alkenone sst record of niop905 shows small changes in sst 0 5 c over the last 23 kyr while that of core 74kl shows a 2 c increase from the last glacial maximum lgm 23 19 calendar cal kyr b p through the holocene the last 11 5 cal kyr b p synchronous with changes in the northern hemisphere in contrast the tex86 records of both cores show a large increase in sst from 22 23 c in the lgm to 28 30 c during termination i 19 11 5 cal kyr b p decreasing to present day annual means of 26 c a cold phase between 14 5 and 12 cal kyr b p that may correspond to the antarctic cold reversal is also observed this implies a southern hemisphere control on tropical sst reconstructed by the tex86 possibly related to sw monsoon our results suggest that the application of both tex86 and u37 0 give different but complementary information on sst developments in past marine environments

evolution of the eastern tropical pacific through plio pleistocene glaciation a tropical pacific climate state resembling that of a permanent el nino is hypothesized to have ended as a result of a reorganization of the ocean heat budget 3 million years ago a time when large ice sheets appeared in the high latitudes of the northern hemisphere we report a high resolution alkenone reconstruction of conditions in the heart of the eastern equatorial pacific eep cold tongue that reflects the combined influences of changes in the equatorial thermocline the properties of the thermocline s source waters atmospheric greenhouse gas content and orbital variations on sea surface temperature sst and biological productivity over the past 5 million years our data indicate that the intensification of northern hemisphere glaciation 3 million years ago did not interrupt an almost monotonic cooling of the eep during the plio pleistocene sst and productivity in the eastern tropical pacific varied in phase with global ice volume changes at a dominant 41 000 year obliquity frequency throughout this time changes in the southern hemisphere most likely modulated most of the changes observed

postdepositional oxic degradation of alkenones implications for the measurement of palaeo sea surface temperatures free and bound long chain alkenones c37 2 and c37 3 in oxidized and unoxidized sections of four organic matter rich pliocene and miocene madeira abyssal plain turbidites one from ocean drilling program site 951b and three from site 952a were analyzed to determine the effect of severe post depositional oxidation on the value of u37k the profiles of both alkenones across the redox boundary show a preferential degradation of the c37 3 compared to the c37 2 compound because of the high initial u37k values and the way of calculating the u37k this degradation hardly influences the u37k profiles however for lower u37k values measured selective degradation would increase u37k up to 0 17 units equivalent to 5 c for most of the u37k band width much smaller degradation already increases u37k beyond the analytical error 0 017 units consequently for interpreting the u37k record in terms of past sea surface temperatures selective degradation needs serious consideration

an offset in tex86 values between interbedded lithologies implications for sea surface temperature reconstructions abstract the tex 86 tetraether index of tetraethers consisting of 86 carbon atoms sea surface temperature sst proxy is based on the distribution of isoprenoid glycerol dialkyl glycerol tetraether gdgt membrane lipids of pelagic thaumarchaeota that are preserved in marine sediments it is a valuable tool for reconstructing past ssts from sedimentary archives however there are still major uncertainties as to the effects of variables other than temperature on the proxy here we present the first study of gdgt variability across early cretaceous interbedded pelagic and shelf sourced turbiditic sediments from two deep sea drilling project dsdp sites in the western north atlantic the results indicate that a small but consistent offset in tex 86 ratios equivalent to 1 2 c of temperature difference occurs between interbedded lithologies of a similar age the offset can be attributed to spatial differences in sea surface temperatures or thaumarchaeotal populations between the shelf and the open ocean or to secondary diagenetic effects related to oxic degradation of the gdgts of these a difference in either thaumarchaeotal taxa or ecology between those living in the shelf and ocean areas seems most plausible regardless of the root cause of the offset these findings highlight the necessity of careful sample selection prior to tex 86 analysis to ensure robust interpretation of palaeotemperature trends

variations in gdgt distributions through the water column in the south east atlantic ocean abstract the tetraether index of 86 carbon atoms tex 86 temperature proxy is widely used in reconstructions of past sea surface temperature most current calibrations are based on surface sediment distributions of the glycerol dialkyl glycerol tetraether lipids gdgts that comprise tex 86 and assume that these gdgts are exported from the upper mixed layer however gdgt export from deeper waters could impact sedimentary gdgt distributions and therefore tex 86 paleothermometry here we examine gdgt distributions in suspended particulate matter spm and underlying sediments collected from the southeast atlantic ocean our results reveal different gdgt distributions specifically the ratio between gdgts bearing 2 vs 3 cyclopentyl moieties 2 3 ratios between surface subsurface 50 200 m and deep water 200 m spm which suggests the occurrence of in situ deep production that is not apparent when considering tex 86 the gdgt distributions in sediments match those of subsurface waters rather than surface waters suggesting that they have not been preferentially derived from the upper mixed layer this is consistent with gdgt abundances being highest in shallow subsurface spm 100 to 200 m it remains unclear what governs the different 2 3 ratios throughout the water column but it is likely related to a combination of temperature and thaumarchaeotal community structure

modifications of the c37 alkenone and alkenoate composition in the water column and sediment possible implications for sea surface temperature estimates in paleoceanography 1 the literature pertaining to c37 alkenone and c37 and c38 alkenoate production and diagenesis has been reviewed and evaluated for issues that might jeopardize their usefulness in paleotemperature estimation we also examined the use of the c37 alkenones as paleoproductivity indicators the stability of their 13c isotopic compositions and their incorporation into the nonsolvent extractable organic matter fraction biological transformation of organic matter by bacteria and zooplankton does not appear to cause significant changes to the ratio of c37 2 and c37 3 alkenones but there are major alterations in the relative composition of alkenoates studies of water column processes and postdepositional sedimentary changes indicate overall stability in the c37 2 c37 2 c37 3 ratio leading to effective preservation of the paleotemperature signal this is not the case for alkenoates and there also appear to be some doubts about the dependence between sea surface temperature and the sedimentary abundance of the c37 4 alkenone c37 alkenones may provide useful qualitative estimates of marine paleoproductivity although these compounds are apparently only derived from haptophycea changes in their quantitative composition might reflect changes in nutrient availability that on sedimentary timescales should also be generally significant of other algal species one caveat is that in highly productive upwelling systems productivity may be expressed mostly in diatom growth and thus not measurable by the c37 alkenones no changes in 13c c37 alkenone composition are observed upon zooplankton ingestion although this is expected from a theoretical perspective further studies are encouraged in order to fully assess the stability of the isotopic signal during c37 alkenone diagenesis finally alkenones bound in the nonextractable fraction of sedimentary organics have not been adequately studied and further work is required to clarify any possible correspondence with a temperature signal

sea surface temperature record of a late cretaceous tropical southern tethys upwelling system abstract late cretaceous sea surface temperatures ssts were reconstructed based on tex 86 data from the unique high productivity upwelling system in the southern tethys margin israel ssts were determined from two oil shale sequences of the santonian early maastrichtian 85 to 68 ma in southern efe syncline and central shefela basin israel paleo latitude 8 15 n these two sampling sites represent the inner and outer belts of the upwelling system our tex 86 data indicate a significant long term sst cooling trend from 36 0 to 29 3 c during the late santonian and the early campanian in the southern tethys margin consistent with the opening of the equatorial atlantic gateway eag based on our data from the equatorial region and literature data from the polar region we reassessed the equator to pole sst gradient to 22 c this value is closer to the modern ocean equator to pole sst gradient 30 c than suggested from previous studies furthermore the sst data suggests the presence of cooler surface water in the inner belt 27 7 c caused by the upwelling system and warmer surface water 29 2 c further seaward in the outer belt

mid latitude southern indian ocean response to northern hemisphere heinrich events abstract the lack of temporal resolution and accurate chronology of southern ocean marine cores has hampered comparison of glacial millennial scale oscillations between the southern ocean antarctic ice and other records from both hemispheres in this study glacial climate variability is investigated over the last 50 ka using a multi proxy approach a precise chrono stratigraphy was developed on the high sedimentation rate core md94 103 indian southern ocean 45 35 s 86 31 e 3560 m water depth by geomagnetic synchronization between the later core and napis75 and 14c dates high resolution time series of 18o in planktonic foraminifera globigerina bulloides and neogloboquadrina pachyderma and sea surface temperatures ssts estimated from the alkenone uk 37 index and foraminifera assemblages have been generated temporal evolution of the two temperature proxy records is notably different during the last glacial period while foraminifera data indicate a consistent cooling towards the last glacial maximum anomalous warm glacial alkenone temperatures suggest a strong advection of warm detrital alkenones by surface waters of the agulhas current superimposed to this general trend during heinrich events foraminiferal ssts point to warmer surface waters while concurrent alkenone ssts exhibit apparent coolings probably caused by enhanced local alkenone production by analogy to modern observations possible influence of enso like conditions on the subantarctic southern ocean ssts is discussed

impact of lateral transport on organic proxies in the southern ocean lateral transport of fine grained organic carbon particles can complicate the interpretation of paleoclimate records based on organic proxies here we investigated the effect of lateral transport on newly developed temperature and soil organic matter proxies tex86 and bit index respectively in core md88 769 recovered from the south east indian ridge our results show that tex86 and bit records in comparison to diatom and foraminifera records were representative for more local climate changes while alkenones and n alkanes originated from distant areas by oceanic and atmospheric transport respectively this suggests that tex86 and bit paleoclimate records are primarily influenced by local conditions and less subjected to long distance lateral transport than other organic proxies in the southern ocean

mid cretaceous albian santonian sea surface temperature record of the tropical atlantic ocean paleoclimate records of geologic time periods characterized by extreme global warmth such as the mid cretaceous are important for a better understanding of the earth9s climate system operating in an exceptionally warm mode here we applied an organic geochemical proxy tex 86 on organic matter rich albian santonian sediments recovered from ocean drilling program leg 207 sites 1258 and 1259 on demerara rise to reconstruct sea surface temperatures ssts in the western equatorial atlantic preceded by a stepwise cenomanian warming trend 31 35 c the onset of the cretaceous thermal maximum coincided here with the cenomanian turonian boundary event once established this extreme warm climate regime characterized by averaged tropical ssts close to 35 c lasted up to the turonian coniacian transition two pronounced cooler intervals 2 3 c interrupt this otherwise remarkably stable record providing the first 18 o independent evidence for middle turonian cooling that previously has been attributed to glacioeustatic sea level lowering coniacian ssts decline stepwise reaching a minimum in the santonian 32 33 c where cooling is most pronounced presumably concomitant with the first progressive opening of a deep water passage through the equatorial atlantic gateway

miocene to pliocene development of surface and subsurface temperatures in the benguela current system 1 the initiation of the benguela upwelling has been dated to the late miocene but estimates of its sea surface temperature evolution are not available this study presents data from ocean drilling program odp site 1085 recovered from the southern cape basin samples of the middle miocene to pliocene were analyzed for alkenone based u37k sstuk and glycerol dialkyl glycerol tetraether gdgt based tex86 temptex water temperature proxies in concordance with global cooling during the miocene sstuk and temptex exhibit a decline of about 8 c and 16 c respectively the temperature trends suggest an inflow of cold antarctic waters triggered by antarctic ice sheet expansion and intensification of southern hemisphere southeasterly winds a temperature offset between both proxies developed with the onset of upwelling which can be explained by differences in habitat alkenone producing phytoplankton live in the euphotic zone and record sea surface temperatures while gdgt producing thaumarchaeota are displaced to colder subsurface waters in upwelling influenced areas and record subsurface water temperatures we suggest that variations in subsurface water temperatures were driven by advection of cold antarctic waters and thermocline adjustments that were due to changes in north atlantic deep water formation a decline in surface temperatures an increased offset between temperature proxies and an increase in primary productivity suggest the establishment of the benguela upwelling at 10 ma during the messinian salinity crisis between 7 and 5 ma surface and subsurface temperature estimates became similar likely because of a strong reduction in atlantic overturning circulation while high total organic carbon contents suggest a biogenic bloom in the pliocene the offset between the temperature estimates and the cooling trend was reestablished

sea surface temperature reconstructions over the last 70 kyr off portugal biomarker data and regional modeling this study aims at providing robust temperature reconstructions for a key oceanographic setting in the north atlantic and at understanding the nature of the temperature signal recorded by the two biomarkers u 37 k and tex86 considering season and depth of production to do so high resolution signals of u 37 k and tex86 are determined for the last 70kyr for core md95 2042 located off portugal signals of u 37 k and tex86 present a tight correlation demonstrating a dominant temperature effect u 37 k signals correspond well to the annual mean sea surface temperature sst whereas tex86h derived temperatures are 5 6 degrees c higher which is unrealistically warm for this area unsuitable tex86 global linear calibrations on the iberian margin may suggest a possible occurrence of archaeal communities with specific temperature response to assess the impact of different season or depth of production of the biomarkers on the recorded temperature in the sediment modeled temperature proxies tproxies are introduced in a regional oceanic modeling system and tested for different seasons annual summer winter and depths surface and 0 200m of production for three climate modes present day pd last glacial maximum lgm and heinrich stadials hs similar temperature amplitudes between climate modes are found at md95 2042 core site for observations for both biomarkers and for modeled annual surface production tproxy 5 5 7 degrees c for t pd lgm and 3 4 degrees c for t lgm hs therefore we propose a new tex86h regional calibration to reconstruct present and past annual mean ssts on the iberian margin

microbial degradation of the marine prymnesiophyte emiliania huxleyi under oxic and anoxic conditions as a model for early diagenesis long chain alkadienes alkenones and alkyl alkenoates to investigate the effect of bacterial diagenesis on the distributions of algal lipids the marine haptophyte emiliania huxleyi was incubated with estuarine sediment slurries under defined conditions oxic sulfate reducing and methanogenic rapid initial degradation of lipids corresponded to increased bacterial populations both of which subsequently declined under oxic conditions the algal c31 dienes were rapidly and completely degraded within 178 days extensive degradation of the characteristic c37 methyl alkenones occurred under all conditions up to 85 under oxic conditions however the u37k index remained essentially constant except for a slight increase at the longest oxic incubation time under anoxic conditions the alkyl alkenoates were preferentially degraded relative to the alkenones and changes in the aa36 index occurred these results demonstrate that lipids are part of the labile organic matter however they were generally degraded at multiple rates which slowed during incubation resulting in their partial preservation hence laboratory experiments conducted over only short periods cannot predict the preservation potential of lipid components furthermore preservation differed between sulfate reducing and methanogenic conditions so the roles of anaerobic processes need to be considered individually with regard to oxic vs anoxic preservation

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

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

evidence for differential degradation of alkenones under contrasting bottom water oxygen conditions implication for paleotemperature reconstruction abstract the successful reconstruction of sea surface temperatures using alkenone paleothermometry u37k has relied on the premise that there is no significant differential degradation of alkenones with different states of unsaturation during diagenetic processes to test this assumption we conducted a comparative study of contemporary sediments in oxic and anoxic bottom waters from the santa monica basin offshore california long chain alkenones were quantified and sea surface temperature were calculated using the calibrated u37k t relationship of prahl et al 1988 our results show that temperature record from the oxic sediments is higher by as much as 4 c compared to those from time equivalent anoxic sediments as a result of differential degradation of long chain unsaturated alkenones and bioturbation mixing in the oxic sediments the differential degradation of c37 3 vs c37 2 alone could account for up to 2 5 c difference between these two records this finding has significant implication in the interpretation of paleo sea surface temperature data using alkenone paleothermometry

provenance and tectonic setting of late carboniferous clastic rocks in west junggar xinjiang china a case from the hala alat mountains abstract the late carboniferous palaeo tectonic setting of the west junggar region is comprised of arcs alternating with basins geochemical analysis of the sedimentary rocks associated with these arc related basins was conducted to better constrain the provenance and tectonic setting major and trace element geochemistry data of late carboniferous mudstones and sandstones in the hala alat mountains suggest that these sedimentary rocks and their source areas are characterized by the following four features 1 sediments experienced a simple recycling process 2 a low degree weathering conditions in the source areas 3 compositional immature of the sedimentary rocks 4 dominated by intermediate to felsic provenance with a few intermediate to mafic sediments integrated with the palaeo flow data and previous authors works a fore arc basin model is proposed for the tectonic setting of the sedimentary rocks the sawur arc is the primary provenance and supplies the major intermediate to felsic detrital fragments the bozchekul chingiz arc and kexia oceanic island arc are the other two secondary sources

sea surface paleotemperature errors in uk 37 estimation due to alkenone measurements near the limit of detection major errors 0 5 c are produced in paleotemperature estimation with the c37 alkenone method when the amount of the diunsaturated or triunsaturated species c37 2 and c37 3 respectively approaches the limit of detection these errors are more commonly encountered with c37 3 because of its higher adsorption to gas chromatographic gc columns they are particularly relevant at low sedimentary c37 alkenone concentrations and may easily increase to temperature differences of 2 4 c depending on the uk 37 values and the ratio between the c37 3 signal and limit of detection mathematical expressions for the description of the analytical constraints derived from this detection limit problem are given a quality assurance guideline based on sample dilution three times and calculation of the sea surface temperature error is proposed for assessment of reliable measurements reevaluation of literature data in the light of the equations reported in the present study suggest that some previously reported alkenone geochemical effects such as variation in uk 37 temperatures due to postdepositional oxidation may reflect deviations in the gc measurements due to changes in c37 alkenone concentration

defunct nile branches inferred from a geoelectric resistivity survey on samannud area nile delta egypt abstract the main objective of this study is to delineate the buried nile channels and the old settlement areas in the samannud area of the nile delta using geoelectric resistivity surveys for this purpose 133 vertical electric soundings ves were conducted using the schlumberger configuration along 13 profiles aligned mainly along a northwest direction i e perpendicular to the expected buried nile channels in addition 10 ves stations were obtained close to boreholes for calibration with the lithological and hydrochemical data these calibrations control the interpretation of the geoelectric resistivity data that are then presented in the form of cross sections and maps the geoelectric cross sections indicate a topmost layer attaining resistivities ranging from 2 5 to 10 ohm m and thickness from 0 5 to 3 m this layer is correlated with the agricultural layer that is mainly affected by the irrigation and agricultural practices the second resistivity layer is relatively thick and shows low resistivities ranging from 1 8 to 9 ohm m which is correlated with the clay and silt layer that forms the subsoil water zone these two layers belong to the holocene bilqas formation the third geoelectric resistivity layer is characterized by its high resistivity ranging from 10 to 220 ohm m which is correlated with the pleistocene sand of mit ghamr formation it was found that the surface of this layer is irregular with localized highs and lows taking into consideration that the holocene nile branches flowed in the low topographic passages on the surface of the pleistocene sand while the high topographic areas were inhibited by the ancient egyptians the courses of buried channels and sand geziras settlement areas are delineated and traced referring to the hieroglyphic inscriptions as well as the interpretation and records of historians and geographers the traced nile branches are mostly parts of the bucolic and the sebennytic branches some local high resistivity lenses at different depths are interpreted as sandy point bars within the low resistivity clay these sandy point bars indicate the locations of stages of the defunct channels that migrated vertically as well as laterally

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

global temperature calibration of the alkenone unsaturation index uk 37 in surface waters and comparison with surface sediments in this paper we compile the current surface seawater c37 alkenone unsaturation uk 37 measurements n 629 1 to 30 c temperature range to derive a global field based calibration of uk 37 with alkenone production temperature a single nonlinear global surface water calibration of uk 37 accurately predicts alkenone production temperatures over the diversity of modern day oceanic environments and alkenone synthesizing populations t 0 957 54 293 uk 37 52 894 uk 37 2 28 321 uk 37 3 r2 0 97 n 567 the mean standard error of estimation is 1 2 c with insignificant bias in estimated production temperature among the different ocean regions sampled an exception to these trends is regions characterized by strong lateral advection and extreme productivity and temperature gradients e g the brazil malvinas confluence in contrast to the surface water data the calibration of uk 37 in surface sediments with overlying annual mean sea surface temperature anno is best fit by a linear model anno 29 876 uk 37 1 334 r2 0 97 n 592 the standard error of estimation 1 1 c is similar to that of the surface water production calibration but a higher degree of bias is observed among the regional data sets the sediment calibration differs significantly from the surface water calibration uk 37 in surface sediments is consistently higher than that predicted from anno and the surface water production temperature calibration and the magnitude of the offset increases as the surface water anno decreases we apply the global production temperature calibration to the coretop uk 37 data to estimate the coretop alkenone integrated production temperature coretop ipt and compare this with the overlying annual mean sea surface temperature anno we use simple models to explore the possible causes of the deviation observed between the coretop temperature signal as estimated by uk 37 and anno our results indicate that the deviation can best be explained if seasonality in production and or thermocline production as well as differential degradation of 37 3 and 37 2 alkenones both affect the sedimentary alkenone signal

comparison and implication of tex86 and u37k temperature records over the last 356kyr of odp site 1147 from the northern south china sea abstract proxy records from the south china sea scs have played an important role in understanding late quaternary scs environmental changes and the east asian monsoon eam variations but few long sea surface temperature sst records have been generated from the scs the recently established tex86 index provides an opportunity to generate long sst records especially for tropical oceans but the applicability and climatic interpretation of the tex86 index for the scs need further study we report and compare orbital scale resolution ca 5 3 kyr tex86 and u37k temperature records of the past 356 kyr for odp site 1147 from the northern scs both records display clear and similar glacial interglacial patterns the u37k sst fluctuated between 22 3 c and 28 3 c with a glacial interglacial difference of 4 5 c while the tex86 temperature fluctuated between 20 3 c and 25 4 c with a slightly smaller glacial interglacial difference of ca 4 c the tex86 temperature has been consistently lower than the u37k temperature over the past 356 kyr consistent with previous studies suggesting that the u37k index is a proxy for sst but the tex86 index is a proxy for subsurface temperature thus it is proposed that the temperature difference t between the u37k and tex86 records reflects mixed layer depth mld changes in the northern scs which fluctuated between 0 3 and 4 0 c with high values mostly during interglacials and lower values mostly during glacial stages mld changes in the northern scs are interpreted to be driven by eam changes with stronger winter monsoon resulting in a deeper mld and a smaller t thus the combination of u37k and tex86 records and their t can be used to reconstruct east asian winter monsoon variations as well as their influences on the hydrographic structure of the scs

the effect of maturity and depositional redox conditions on archaeal tetraether lipid palaeothermometry recently we proposed a new organic sea surface temperature proxy tex86 based on the distribution of archaeal tetraether lipids here we have examined the effect of oxic degradation and maturity on this new temperature proxy our results show that oxic degradation does not appear to affect the tex86 values within the analytical error hydrous pyrolysis experiments suggest that thermal maturity does have an effect on tex86 sediments with relatively high amounts of 22s hopanes 22s 22s 22r ratios 0 1 or 17 21 h hopanes ratios 0 5 may have tex86 values which are biased towards lower values and thus lower sea surface temperatures

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

molecular stratigraphy a new tool for climatic assessment variations in sea surface temperatures over the past 500 000 years are inferred from the relative abundance behaviour of two organic compounds c37 alkenones over the upper 8 metres of a sediment core from the eastern equatorial atlantic this molecular record ascribed to contributions from prymnesiophyte algae correlates well with the variations in the 18 signal for the calcareous skeletons of certain planktonic foraminifera thus providing the first demonstration of a new stratigraphical technique which may be especially valuable where methods based on carbonate 18 fail

distributional variations in marine crenarchaeotal membrane lipids a new tool for reconstructing ancient sea water temperatures it has recently been shown that membrane lipids of marine crenarchaeota a ubiquitous and abundant component of plankton occur in relatively high concentrations in recent and ancient sediments in this study we investigated the environmental controls on the relative distribution of these lipids in surface sediments we especially focussed on temperature as it is known from the thermophilic genetic relatives of marine crenarchaetoa that the composition of their membrane strongly depends on growth temperature indeed a significant linear correlation r2 0 92 is found between the number of cyclopentane rings in sedimentary membrane lipids derived from marine crenarchaeota and the annual mean sea surface temperatures this suggests that the mechanism of physical adaptation of their membrane compositions to temperature is identical to that of their thermophilic relatives in turn archaeal lipid distributions in sediments may thus allow the reconstruction of sea water temperatures of ancient marine environments

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

temperature dependent variation in the distribution of tetraether membrane lipids of marine crenarchaeota implications for tex86 paleothermometry 1 recently a new geochemical temperature proxy the tex86 was introduced this proxy is based on the number of cyclopentane moieties in the glycerol dialkyl glycerol tetraethers gdgts of the membrane lipids of marine crenarchaeota which changes as a response to temperature however until now only sediment data have been used to establish this proxy and experimental work is missing we performed mesocosm studies with marine crenarchaeota incubated at temperatures ranging from 5 to 35 c and salinities of 27 and 35 to test the validity of the tex86 proxy growth of marine crenarchaeota in these mesocosms was evident from the substantial increase in the concentration of marine crenarchaeotal membrane lipids with amounts up to 3400 ng l with increasing temperature an increase in the number of cyclopentane moieties in the crenarchaeotal membrane lipids was observed different salinities did not show any effect on the gdgt distribution the tex86 showed a significant linear correlation to incubation temperature tex86 0 015 t 0 10 r2 0 79 this equation has a similar slope to the correlation obtained from core tops but differs in the intersection tex86 0 015 t 0 28 r2 0 92 this difference is mainly determined by the smaller amount of the regioisomer of crenarchaeol in the incubation series compared to core top samples these incubation experiments indicates that water temperature is indeed the major controlling factor for the membrane distribution of marine crenarchaeota and confirms that the tex86 proxy depends on a physiological response to regulate membrane fluidity

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

timing and stepwise transitions of the african humid period from geochemical proxies in the nile deep sea fan sediments large fluvial systems such as the nile river allow a basin scale integrated view of climatological and environmental changes in this study we reconstructed the nile discharge history for the last 20 ka using molecular ratios of glycerol dialkyl glycerol tetraethers gdgts and neodymium nd radiogenic isotopes by characterizing both the organic and inorganic fractions we assessed the relevance of the gdgt based proxies in deltaic environments as tracers of terrigenous origin a large increase in nile discharge is documented from 14 8 to 8 4 ka bp reflecting enhanced physical erosion and transport processes from the ethiopian traps we confirmed the primary control of insolation on precipitation on north east africa through the last 20 ka the centennial time resolution reached on the sedimentary sequence revealed a step wise onset and termination of the african humid period ahp starting at 14 8 ka and ending at 8 4 ka bp respectively our centennial millennial records allowed furthermore pinpointing the abrupt periods of arid conditions corresponding to the younger dryas these data illustrate the linkage between low and high latitude hydrological variability

alteration processes of alkenones and related lipids in water columns and sediments 1 alkenones produced by the haptophyte algae are currently being used as indices of sea surface temperature in recent and past ocean environments but limited information is available concerning the impact of biotic and abiotic processes on the integrity of these long chain lipids this synthesis provides selected background information on major alteration processes that must be considered before such indices can be used with confidence a number of processes in the water column and surface sediments have the potential to impact the structural integrity of alkenones and compromise their ability as temperature markers processes discussed include the alteration of alkenone structure during early diagenesis direct biotic and abiotic impacts and the effect of digestive processes by grazers current literature suggests that despite substantial changes in concentration from biological processing the temperature signal is preserved for each of these processes information on the integrity of the alkenone isotopic signature is also needed and limited information available is reviewed in addition to the alkenones related lipids including the long chain alkadienes and akyl alkenoates that might serve as ancillary markers are discussed

fidelity of alkenone paleotemperatures in southern cape basin sediment drifts 0 in two drift cores tn057 21 and ocean drilling program site 1089 are nearly identical during the interval of overlapping analyses mis 4 5c ssts in a nearby nondrift core tn057 6 covary with those in core tn057 21 throughout mis 1 5c while climatological ssts overlying tn057 21 and tn057 6 are similar and consistent with reconstructed holocene ssts in the nondrift core surface waters overlying tn057 21 are 6 c colder than holocene alkenone ssts in the drift core temperatures remain 6 c warmer in tn057 21 relative to tn057 6 during the 100 kyr duration of the records we hypothesize that alkenone derived ssts in tn057 21 are higher than climatological ssts in the overlying surface water and those in tn057 6 as a result of the winnowing and focusing of sedimentary alkenones produced in warmer waters to the north climatological ssts in the central and northern cape basin are 16 20 c a 1 5 offset of fine fraction d 18 o values relative to planktonic foraminifera in tn057 21 supports this hypothesis temporal changes in sediment focusing were evaluated directly using uranium series radioisotopes while higher sediment focusing factors would be expected to result in higher alkenone derived ssts if sediment advection were the primary control on down core changes in alkenone derived ssts 230 th derived focusing factors indicate no such correlation exists we conclude that alkenone paleotemperature reconstructions from southern cape basin drifts reliably record regional sst variations in the cape basin index terms 4267 oceanography general paleoceanography 1055 geochemistry organic geochemistry 1040 geochemistry isotopic composition chemistry 3022 marine geology and geophysics marine sediments processes and transport keywords alkenones cape basin thorium