marine crenarchaeotal membrane lipids in decapods implications for the tex86 paleothermometer pelagic crenarchaeota produce glycerol dibiphytanyl glycerol tetraethers gdgts as membrane lipids and the gdgt composition changes according to growth temperature this forms the basis of the tex86 paleotemperature proxy this ratio correlates with sea surface temperature sst despite the fact that crenarchaeota are distributed through the water column therefore there must be mechanisms that transport the surface signal to sediments such as repackaging in fecal pellets marine snow mass falls after phytoplankton blooms or daily migration to study gdgt transport we analyzed stomachs and intestines of atlantic and mediterranean decapods as they are one of the major megafaunal groups are easy to sample and occur in both pelagic and benthic environments gdgts were found in most decapods guts gdgt abundances are significantly lower in intestines but tex86 derived temperatures are not significantly different between stomachs and intestines 1oc suggesting that tex86 values are not altered during gut transit atlantic decapods show no difference in tex86 values between benthic detritivors and pelagic predators however mediterranean decapods show a substantial difference between macroplankton feeders and bentho pelagic predators this is probably related to the freshness of the material consumed tex86 derived temperatures in atlantic decapods are close to the sst around the time of sampling in agreement with stomach content analysis that shows fresh organic matter being ingested for mediterranean decapods tex86 temperatures are significantly higher than sst around the time of sampling this can be partly attributed to the large variability between decapod specimens and the low amounts of fresh material found in their stomachs

glacial interglacial variablity in the benguela upwelling system spatial distribution and budgets of organic carbon accumulation 1 modern sedimentary total organic carbon toc content as a proxy for surface water export production was mapped on the shelf and on the upper continental slope of the benguela upwelling system using 137 core tops shelf maxima in toc can be correlated with maxima in surface water productivity on the slope high toc contents are observed offshore from sites of strong modern upwelling estimates of modern toc mass accumulation rates mar show that approximately 85 of the total is accumulating on the shelf toc mar were calculated mapped and budgeted for the holocene and for the last glacial maximum lgm using 19 sediment cores from the continental slope during the lgm centers of deposition and production have migrated offshore with respect to their holocene positions toc accumulation on the continental slope was approximately 84 higher during the lgm than during the holocene possibly reflecting enhanced productivity the toc distribution patterns and sediment echo sounding data suggest that undercurrents strongly influence the sedimentation off namibia winnowing and focusing result in great lateral heterogeneity of sedimentation rates and sediment properties individual cores therefore do not necessarily reflect general changes in export production these results highlight the need for detailed regional studies based on a large number of sediment cores for highly heterogeneous high productivity areas in order to derive general statements on total fluxes

mineralogy and geochemistry of the clay fraction of sediments from the namibian continental margin and the adjacent hinterland the continental shelf off namibia can be divided into two sectors at latitude 18 40 s based on the distinctive morphologies of the two regions and on differences in composition of their surficial sediments the kunene shelf is narrow shallow and covered mainly by terrigenous sediment whereas the walvis shelf is wide deep and supports predominantly biogenic sediment the walvis shelf also possesses a number of distinguishing features its outer region has a concave profile which is attributed to upbuilding of the inner shelf during periods of lowered sea level its inner region is covered by an extensive belt of diatomaceous mud parallel to the coast the seaward and landward flanks of this deposit differ in lithology due mainly to the advanced state of dissolution of opal in deep water and to the influx of aeolian terrigenous detritus especially illite close to shore long belts of terrigenous mud extend southwards from both the kunene and orange rivers the currents responsible for transporting this sediment are poleward directed tongues of the angola benguela front in the north and mixed poleward moving south atlantic central water in the south the kunene river carries more smectite to the sea than the much larger orange the distribution of clay minerals on the continental shelf follows that of the adjacent hinterland with smectite and to a lesser extent kaolinite being significant in the north and illite predominating in the south along the upper slope the concentrations of smectite and kaolinite increase due to their importation from the kunene river by poleward directed antarctic intermediate water the geochemical character of riverine clays reflects the rock types exposed in each of the drainage basins compared with marine sediments these clays are enriched in eight of the fourteen elements investigated namely al fe mg co mn pb rb and zn in contrast the offshore element distribution patterns show little resemblance to the patterns of individual drainage basins clays in the marine sediments are enriched relative to the river sediments in ca k cd ni and sr five lithofacies recognized in the unconsolidated marine sediments are based on the relative proportions of opal calcium carbonate phosphorite glauconite and terrigenous components average element concentrations of individual lithofacies are enriched relative to the river clays in cd diatomaceous facies ca cd ni and sr calcareous and facies k and ni slightly glauconitic facies cd and sr terrigenous facies regionally the clay fractions of unconsolidated marine sediments contain high concentrations of al fe mg k mn and rb on the kunene margin due to aluminosilicates being imported by the kunene river ca and sr reach high values on the walvis outer margin in response to upwelling along the coast maximum concentrations of cd are associated with diatomaceous mud on the walvis inner shelf cu ni and zn reach high levels at a few spot locations where organic matter morg has suffered little dilution from other components especially opal and pb is concentrated with glauconitic sediment on the kunene shelf semi consolidated sediments are exposed intermittently on the outer margin they provide evidence that the palaeoclimate became much drier in post miocene times but in the north this picture is complicated by the introduction of sediment from the kunene river during the late tertiary palaeo oceanographic evidence suggests that the northern part of the study area experienced a concomitant decrease in productivity while in the southern part productivity increased

lack of evidence for enhanced preservation of sedimentary organic matter in the oxygen minimum of the gulf of california a test of the hypothesis that hydrogen rich organic matter accumulates preferentially in sediments under oxygen minima has been carried out by examining the composition of laminated and homogeneous diatomaceous sediments of the guaymas basin in the gulf of california the laminated sediments occur where an intense oxygen minimum intersects the slope around the margins of the basin above and below the depth of the oxygen minimum the sediments are homogenized by a burrowing infauna the two sediment types have very similar bulk chemical and mineral compositions and the organic matter is overwhelmingly marine the total organic carbon contents and rock eval parameters hydrogen and oxygen indices of the two sediment types are not significantly different whereas a road organic carbon maximum in the homogeneous sediments is centered at roughly 1200 m depth on the slope of the basin this maximum lies deeper than the core of the oxygen minimum thus both the concentration and the nature of the organic matter in the sediments of this highly productive marginal marine basin are not related to the concentration of dissolved oxygen in the bottom waters

multi proxy reconstruction of terrigenous input and sea surface temperatures in the eastern gulf of guinea over the last 35 ka abstract the tight coupling between the atmospheric and oceanic circulation in the equatorial atlantic region makes this area an important region for paleoclimatic research previous studies report the occurrence of large amounts of terrigenous material and soil organic carbon soc within the marine sediments of the eastern gulf of guinea we use the accumulation rates ar of branched glycerol dialkyl glycerol tetraethers gdgts to identify variations in soc delivery to the niger fan over the last 35 ka and compare these records to long chain n alkanes as a proxy for higher plant material to an inorganic proxy for terrigenous input aluminum ar and to indicators for the marine productivity ar of carbonate and crenarchaeol in addition sea surface temperatures ssts are calculated based on the tex 86 h index and environmental factors affecting the sst reconstructions are discussed our results indicate that al ar are closely connected to the rate of mean sea level change after 15 ka bp with an additional influence of the increased monsoonal precipitation and extended vegetation cover corresponding to the african humid period 14 8 5 5 ka bp branched gdgt ar appears to be determined by shelf erosion in addition to the interplay of monsoonal precipitation and vegetation cover controlling soil erosion long chain n alkane concentrations clearly show a different trend than the other proxies which might be due to their predominant eolian transport paleo ssts show a clear shift from colder temperatures during the last glacial period 20 22 c to warmer temperatures during the holocene 24 26 c however tex 86 h based ssts are cold biased compared to recent ssts and mg ca based sst reconstructions which is probably caused by a high seasonality of the thaumarchaeota with a maximum productivity of these organisms during the cold summer months however a sub surface production of gdgts and or a potential bias of sst reconstruction by terrestrial input could not be completely excluded

archaeal tetraether lipids record subsurface water temperature in the south china sea abstract the south china sea scs is the largest tropical marginal sea in the western pacific ocean while the u 37 k proxy is known to reflect the sea surface temperature sst of the 0 30 m mixed layer in the scs little is known about the applicability of the tex86 proxy here we present results from paired analyses of tex 86 h a modified version of tex86 and u 37 k from core top sediment samples from the scs tex 86 h based sst calculated from the global regression exhibited slightly higher values avg 28 7 c range 27 1 30 3 c than values from the world ocean atlas 1994 avg 27 4 c range 26 1 28 6 c and u 37 k based temperature values avg 27 3 c range 26 1 29 0 c moreover the linear relationship between tex 86 h and sst was poor r2 0 44 correlation analysis of tex 86 h with annual temperature and seasonal temperature at various depths revealed that tex 86 h correlated better with annual sea temperature at 30 125 m r 0 89 than with temperature in the 0 30 m mixed layer r 0 69 this suggests that tex 86 h reflects a deeper and cooler subsurface temperature rather than surface or mixed layer temperature in the scs as a result the global regression which results in higher sst values could not be applied to predict subsurface temperature in the scs and a local calibration of tex 86 h vs 30 125 m subsurface temperature was tentatively established furthermore the difference between u 37 k and tex 86 h derived temperature talkenone gdgt correlated moderately r 0 62 with the depth of the thermocline of the 18 c isotherm in the scs suggesting that the difference may provide a proxy for upper ocean vertical thermal gradient in this marginal sea

comparison of pelagic and nepheloid layer marine snow implications for carbon cycling abstract marine snow from upper and mid water i e pelagic depths on the california margin is texturally and compositionally different from that traveling in the nepheloid layer transmission electron microscopy shows that pelagic marine snow consists primarily of bioclasts e g diatom frustules foram tests organic matter and microbes these components are entrained as discrete particles or small aggregates 10 m in diameter in a loose network of exocellular muco polysaccharide material clays are infrequent but when present are constituents of comparatively compact organic rich microaggregates microbes are abundant and appear to decrease in number with increasing water depth in contrast marine snow aggregates collected from just above the sea floor in the nepheloid layer are assemblages of clay particles clay flocs and relatively dense clay organic rich microaggregates in an exocellular organic matrix bioclasts and microorganisms occur only rarely the prevalence of clay organic rich aggregates in the nepheloid layer suggests that prior to final deposition and burial marine snow from the pelagic zone is subject to disaggregation and recombination with terrigenous detrital material near or at the sea floor results have significant implications for the accumulation and burial rates of organic carbon on continental margins and the aging and bioavailability of sedimentary organic matter samples examined were collected offshore of northern and central california

bedrock topography from magnetic anomalie an aid for groundwater exploration in hard rock terrains the role of the magnetic method in groundwater exploration is to locate structures such as dikes faults fractures etc that control the accumulation and movement of groundwater in hard rock terrains the thickness of the weathered layer is an important parameter that determines the quantity of groundwater accumulated in the unconfined aquifer above the basement the basement rock in the process of weathering loses its magnetic properties and becomes much less magnetic therefore the magnetic response is mostly due to the unweathered hard basement rock and the depths of magnetic sources obtained from the analysis give us the top of the basement information about the thickness of the weathered layer would help in assessing the groundwater potential of the region

the north chilean coast range an example for the development of an active continental margin analysis of extended plutons in the coast range of north chile between 25 30 and 26 35 led to the recognition of a complex magmatic and structural evolution from the upper paleozoic to the tertiary

glycerol dialkyl glycerol tetraethers and tex86 index in sinking particles in the western north pacific abstract seasonal and depth variation in the flux of glycerol dialkyl glycerol tetraethers gdgts and tex 86 tex 86 h and tex 86 l values in sinking particles was examined by conducting a 21 month time series sediment trap experiment at a mooring station wct 2 39 n 147 e in the mid latitude nw pacific the aim was to understand the sinking process of gdgts in the water column and the preservation of the tex 86 signal in the water column and sediment surface in the shallow trap the sinking flux of gdgts showed maxima from may 1998 to february 1999 the maximal peaks in sinking flux corresponded to peaks in the sinking flux of organic carbon opal and lithogenic material gdgt concentration in the total fine fraction and the caldarchaeol crenarchaeol ratio at three depths ca 1300 4800 m varied synchronously implying rapid vertical transport of gdgts to deeper water with a sinking velocity 260 m day 1 below ca 1300 m the changes in tex 86 based temperature were different from those in contemporary sea surface temperature sst the former was lower than the sst from may to december and corresponded to the temperature at the thermocline whereas it was higher than the sst from december to may the annual average sinking flux of the gdgts decreased with depth the gdgt half depth the depth range over which half of the gdgt is lost was calculated to be 3108 3349 m implying that gdgts were well preserved during sinking the flux weighted average tex 86 based temperature was constant with depth and corresponded roughly to mean annual sst the findings support a previous hypothesis that the gdgts produced in surface water are preferentially delivered to the deeper water column via grazing and repackaging in larger particles the constant tex 86 at different depths indicates that it was not affected by degradation in the water column the preservation efficiency of gdgts was 1 0 1 3 at the water sediment interface despite significant gdgt degradation there was a small difference in tex 86 values between sinking particles and surface sediment

paleoceanographic implications of the difference in deep sea sediment mixing between large and fine particles more and more paleoceanographic studies are performed on different size fractions of deep sea sediments although it has been a controversial issue for some time the bioturbation process depends on the particle size and can in principle decouple paleoceanographic records obtained in the same core this problem is studied by using a simple mixing model which allows the derivation of analytical equations for both the expected phase shift and relative attenuation of signals carried by different size fractions depending on several parameters the time shift and relative attenuation can be on the order of a few millenia and 50 respectively however high sedimentation rates 10 20 cm kyr minimize these potential complications allowing us to study millenium scale events in well chosen sedimentary environments

glacial interglacial variation in organic carbon burial on the slope of the n w european continental margin 48 50 n the sources and fate of organic carbon corg were examined at two sites on the goban spur and a single site within the porcupine sea bight on the n w european slope between 48 n and 50 n here we present data on the sedimentary corg concentration its 13c 12c composition 13corg and corg n of 224 total and 119 fine fraction 63 m samples as a time series running from the instantaneous marker horizon heinrich layer 2 25 5 ka bp through the last glacial isotope stage 2 and interglacial isotope stage 1 to the present the significance of the n w european slope as a depositional sink for corg has declined in the past twenty thousand years with flux values decreasing two to three fold from the late glacial 60 70 mg c cm 2 ka 1 to low late holocene values significant shifts are seen in the 13corg signature of both the total and fine fractions between the present interglacial and last glacial the open slope of the goban spur is characterised by relatively low values over the last glacial with minimum values for the total sediment of around 24 5 occurring at ca 18 ka bp and generally increasing values during the holocene with the most recent samples having values of ca 19 2 to 20 2 in the porcupine sea bight a different relationship is evident with samples from the last glacial maximum being generally higher while values from the holocene are lower with a minimum of 23 3 occurring just below the mixed layer similar trends are observed in the fine fraction albeit with a different dynamic range paired analysis of 13corg and corg n are consistent with the organic matter being a climatically forced mixture from c3 photosynthetic terrigenous and marine organic matter sources an increased influence of terrestrial corg is suggested on the glacial goban spur and holocene porcupine sea bight and vice versa we suggest that this may be explained by modern wind driven flushing of terrigenous carbon across the armorican and celtic shelves to the n w and thence into porcupine sea bight during the last glacial increased strength of westerly winds created a residual current regime driving material to the s w where it was transported in vigorous tidal off shelf flushing to the upper slope followed by slope current transfer to the goban spur much of this material was presumably delivered by the great channel river to the outer shelf thus leading to enhanced flux of terrestrial corg on the goban spur the influence of a freshwater plume from meltwater discharge of the european ice sheet in this region is supported by foramininiferal 18o data from which a palaeo salinity reconstruction shows a greatest negative anomaly of 2 55 that is s 35 at the time of maximum terrestrial corg content in the sedimentary material in addition to showing that surface waters over goban spur were relatively fresh throughout the glacial our results also reveal variability in surface salinity on shorter timescales

geochemistry petrology and origin of the cenozoic volcanic rocks of the northern andes in ecuador abstract the cenozoic volcanic rocks of the northern andes in ecuador for which only little petrological and geochemical information was available until now display a strong geochemical and petrological zoning from west to east the magmas of the volcanoes of the western cordillera wc are unique to the andes they belong to andesite plagidacite series which is characterized by low and fairly constant k 2 o contents 1 0 2 low abundances of large cation elements rb sr ba rare earth elements highly charged cations zr u th and relatively high ni and cr abundances the magmas of the volcanoes of the eastern cordillera ec belong to andesite andesitedacite rhyolite series which is characterized by rb sr ba ree zr u and th contents higher than in the rocks of the wc and varying with the k 2 o content they have ni and cr versus mgo correlations similar to the rocks of the western cordillera even higher contents of k 2 o and the above mentioned elements are encountered in the volcanic rocks of the sub andean area saa all of the rocks have the same 37 sr 36 sr ratio of 0 704 the rocks are chemically more closely related to the mesozoic to tertiary rocks of the basic igneous complex bic of ecuador and colombia than to those of the central andes it is suggested that the cenozoic magmas of the volcanoes of the western and eastern cordillera originated by hydrous partial melting of amphibolites and garnet amphibolites of the bic type in a subduction zone beneath the cordilleras at pressures near 20 kbar which corresponds to a depth of about 70 km

reconstruction of the last deglaciation deconvolved records of δ18o profiles micropaleontological variations and accelerator mass spectrometric14c dating bioturbation acts as a low pass filter in displacing and reducing the amplitudes of stratigraphic signals this often leads to a loss of high frequency events in the stratigraphic record in addition when considering an isotopic signal 18o 14c measured in stratigraphic carriers such as foraminifera bioturbation and carrier abundance changes can create artifacts which may be falsely interpreted as leads or lags in the paleoclimatic record

a combined o sr nd and pb isotopic and trace element study of crustal contamination in central andean lavas i local geochemical variations systematic variations in o sr nd and pb isotopic ratios and in sr nd pb and rb trace element abundances in central andean andesitic lavas are analyzed in terms of combined crustal assimilation and fractional crystallization the results of integrated isotopic model calculations show that observed local isotopic and trace element variations within the arequipa and barroso volcanic groups of southern peru are best fit by a simple model involving shallow or intermediate depth crustal assimilation of charcani gneiss or an equivalent rock accompanied by dominantly plagioclase fractional crystallization a consequence of this result is that the rbsr pseudoisochrons reported for the arequipa and barroso volcanics are wholly artifacts of the combined processes of assimilation and plagioclase fractionation as are all of the pb isotopic variations measured in the same lavas already interpreted by tilton and barreiro 14 to be the result of crustal contamination isotopic and trace element compositions of the primary magmas for the arequipa and barroso volcanic series are obtained by correcting for assimilation and fractional crystallization the starting magmas are characterized over the entire range of permissible primary compositions by high87sr 86sr ratios low143nd 144nd ratios and high sr concentrations relative to normal island arc andesites these results appear to require prior contamination of the magmas but not involving plagioclase fractionation the uncertainty in pb and o isotope ratios computed for possible primary magmatic compositions is sufficiently large however that it is not possible to preclude a subcrustal origin for at least some regional variation in sr and nd isotopic ratios

the displacement field of the landers earthquake mapped by radar interferometry geodetic data obtained by ground or space based techniques can be used to infer the distribution of slip on a fault that has ruptured in an earthquake although most geodetic techniques require a surveyed network to be in place before the earthquake1 3 satellite images when collected at regular intervals can capture co seismic displacements without advance knowledge of the earthquake s location synthetic aperture radar sar interferometry first introduced4 in 1974 for topographic mapping5 8 can also be used to detect changes in the ground surface by removing the signal from the topography9 10 here we use sar interferometry to capture the movements produced by the 1992 earthquake in landers california11 we construct an interferogram by combining topographic information with sar images obtained by the ers 1 satellite before and after the earthquake the observed changes in range from the ground surface to the satellite agree well with the slip measured in the field with the displacements measured by surveying and with the results of an elastic dislocation model as a geodetic tool the sar interferogram provides a denser spatial sampling 100 m per pixel than surveying methods1 3 and a better precision 3 cm than previous space imaging techniques12 13

airborne gravimetry from a small twin engine aircraft over the long island sound in january 1990 a test of the feasibility of airborne gravimetry from a small geophysical survey aircraft a cessna 404 was conducted over the long island sound using a bell aerospace bgm 3 sea gravity meter gravity has been measured from large aircraft and specially modified de havilland twin otters but never from small standard survey aircraft the gravity field of the long island sound is dominated by an asymmetric positive 30 rngal anomaly which is well constrained by both marine and land gravity measurements using a trimble 4000 gps receiver to record the aircraft s horizontal position and radar altimeter elevations to recover the vertical accelerations gravity anomalies along a total of 65 km were successfully measured the root mean square rms difference between the airborne results and marine measurements within 2 km of the flight path was 2 6 mgai for 15 measured values the anomalies recovered from airborne gravimetry can also be compared with the gridded regional free air gravity field calculated using all available marine and land gravity measurements the rms difference between 458 airborne gravity measurements and the regional gravity field is 2 7 mgai this preliminary experiment demonstrates that gravity anomalies with wavelengthsas short as 5 km can be measured from small aircraft with accuracies of 2 7 mgal or better the gravity measurements could be improved by higher quality vertical and horizontal positioning and tuning the gravimeter s stabilized platform for aircraft use

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

temporal and spatial variation in tetraether membrane lipids of marine crenarchaeota in particulate organic matter implications for tex86 paleothermometry the tex86 is a new temperature proxy which is based on the number of cyclopentane moieties in the glycerol dialkyl glycerol tetraether gdgt lipids of the membranes of crenarchaeota that occur ubiquitously in oceans and shelf seas this proxy was calibrated by core top sediments but it is as yet not clear during which season and at which depth in the water column the gdgt signal used for tex86 paleothermometry is biosynthesized here we analyzed 200 particulate organic matter pom samples from 11 different marine settings for tex86 this revealed that the gdgts occur seasonally in surface waters and occur in higher abundances during the winter and spring months the depth distribution showed that gdgts generally appeared in higher amounts below 100 m depth in the water column however the tex86 values for waters below the photic zone 150 1500 m did not correlate with the in situ temperature but rather correlated linearly with surface temperature the tex86 for pom from the upper 100 m showed a linear correlation with in situ temperature which was nearly identical to the previously reported core top equation the correlation of all pom samples with surface temperature was also strikingly similar to the core top correlation these findings demonstrate that the gdgt signal which reaches the sediment is mainly derived from the upper 100 m of the water column this may be caused by the fact that gdgts from the photic zone are much more effectively transported to the sediment by grazing and repackaging in large particles than gdgts from deeper waters

an airborne gravity study of eastern north carolina the naval research laboratory nrl has developed a prototype airborne gravity measurement system the core of the system is a lacoste and romberg air sea gravity meter mounted on a three axis stable platform corrections to the gravimeter data for altitude and variations in altitude are determined from a combination of highly precise radar and pressure altimeters the original prototype system was designed for use over oceanic areas we recently incorporated the pressure measurement to extend use of the airborne system to terrestrial regions where occasional radar altitudes over points of known topographic height can be obtained the radar heights are used to relate the pressure altitudes to absolute altitudes and to determine the slopes of the isobaric surfaces vertical accelerations due to horizontal velocity over a curved rotating earth the eotvos correction and precise two dimensional positions are determined from a texas instrument p code global positioning system the updated system was tested

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

ensialic spreading subsidence in the mesozoic and palaeogene andes of central chile an oceanic plate subducting eastwards below a continental margin and resulting in crustal shortening can be inferred to have been active in central chile during the palaeozoic however the geological record for the mesozoic and palaeogene shows evidence of a persistent tensional regime and absence of crustal shortening although lateral asymmetry inherent to a subducting model is shown by this record a bilateral symmetry is also well substantiated a coupled action of plate subduction and spreading subsidence the latter taking place within the margin of a continental plate is suggested to explain these features

lateral transport controls distribution quality and burial of organic matter along continental slopes in high productivity areas in this study we demonstrate the relevance of lateral particle transport in nepheloid layers for organic carbon oc accumulation and burial across high productive continental margins we present geochemical data from surface sediments and suspended particles in the bottom nepheloid layer bnl from the most productive coastal upwelling area of the modern ocean the benguela upwelling system offshore southwest africa interpretation of depositional patterns and comparison of downslope trends in oc content organic matter composition and 14 c age between suspended particles and surface sediments indicate that lateral particle transport is the primary mechanism controlling supply and burial of oc we propose that effective seaward particle transport primarily along the bnl is a key process that promotes and maintains local high sedimentation rates ultimately causing high preservation of oc in a depocenter on the upper slope offshore namibia as lateral transport efficiently displaces areas of enhanced oc burial from maximum production at highly productive continental margins vertical particle flux models do not sufficiently explain the relationship between primary production and shallow marine oc burial on geologic time scales the widest distribution and strongest intensity of lateral particle transport is expected during periods of rapid sea level change at times in the geologic past widespread downslope lateral transport of oc thus may have been a primary driver of enhanced oc burial at deeper continental slopes and abyssal basins

merging late holocene molecular organic and foraminiferal based geochemical records of sea surface temperature in the gulf of mexico 1 a molecular organic geochemical proxy tex86 for sea surface temperature sst is compared with a foraminifera based sst proxy mg ca in a decadal resolution marine sedimentary record spanning the last 1000 years from the gulf of mexico we assess the relative strengths of the organic and inorganic paleoceanographic techniques for reconstructing high resolution sst variability during recent climate events including the little ice age lia and the medieval warm period mwp sst estimates based on the molecular organic proxy tex86 show a similar magnitude and pattern of sst variability to foraminiferal mg ca sst estimates but with some important differences for instance both proxies show a cooling 1 c 2 c of gulf of mexico ssts during the lia during the mwp however mg ca ssts are similar to near modern ssts while tex86 indicates ssts that were cooler than modern using the respective sst calibrations for each proxy results in tex86 sst estimates that are 2 c 4 c warmer than mg ca sst throughout the 1000 year record we interpret the tex86 sst as a summer weighted sst signal from the upper mixed layer whereas the mg ca sst better reflects the mean annual sst downcore differences in the sst estimates between the two proxies t tex86 mg ca are interpreted in the context of varying seasonality and or changing water column temperature gradients

organic carbon accumulation and preservation in surface sediments on the peru margin concentrations and characteristics of organic matter in surface sediments deposited under an intense oxygen minimum zone on the peru margin were studied in samples from deck deployed box cores and push cores acquired by submersible on two transects spanning depths of 75 to 1000 m at 12 and 13 5 s the source of organic matter to the seafloor in these areas is almost entirely marine material as confirmed by the narrow range of of organic carbon obtained in the present study 20 3 to 21 6 pdb and the lack of any relationship between pyrolysis hydrogen index and carbon isotope composition organic carbon contents are highest up to 16 on the slope at depths between 75 and 350 m in sediments deposited under intermediate water masses with low dissolved oxygen concentrations 5 mol kg even at these low concentrations of dissolved oxygen however the surface sediments that were recovered from these depths are dominantly unlaminated strong currents up to 30 cm s associated with the poleward flowing peru undercurrent were measured at depths between 160 and 300 m on both transects the seafloor in this range of water depths is characterized by bedforms stabilized by bacterial mats extensive authigenic mineral crusts and or thick organic flocs constant advection of dissolved oxygen although in low concentrations active resuspension of surficial organic matter activity of organisms and transport of fine grained sediment to and from more oxygenated zones all contribute to greater degradation and poorer initial preservation of organic matter than might be expected under oxygen deficient conditions dissolved oxygen concentrations ultimately may be the dominant affect on organic matter characteristics but reworking of fine grained sediment and organic matter by strong bottom currents and redeposition on the seafloor in areas of lower energy also exert important controls on organic carbon concentration and degree of oxidation in this region

airborne gravity measurement over sea ice the western weddell sea an airborne gravity study of the western weddel sea east of the antarctic peninsula has shown that floating pack ice provides a useful radar altimetric reference surface for altitude and vertical acceleration corrections surface for alititude and vertical acceleration corrections to airborne gravimetry airborne gravimetry provides an important alternative to satellite altimetry for the sea ice covered regions of the world since satellite alimeters are not designed or intended to provide accurate geoidal heights in areas where significant sea ice is present within the radar footprint errors in radar corrected airborne gravimetry are primarily sensitive to the variations in the second derivative of the sea ice reference surface in the frequency pass band of interest with the exception of imbedded icebergs the second derivative of the pack ice surface closely approximates that of the mean sea level surface at wavelengths 10 20 km with the airborne method the percentage of ice coverage the mixture of first and multi year ice and the existence of leads and pressure ridges prove to be unimportant in determining gravity anomalies at scales of geophysical and geodetic interest provided that the ice is floating and not grounded in the weddell study an analysis of 85 crosstrack miss ties distributed over 25 data tracks yieldsmore an rms error of 2 2 mgals significant structural anomalies including the continental shelf and offsets and lineations interpreted as fracture zones recording the early spreading directions within the weddell sea are observed in the gravity map less

attenuation of millennial scale events by bioturbation in marine sediments the discovery of large millennial scale oscillations 1 10 kyr period in climate records from ice cores and marine sediments in the north atlantic has motivated the search to understand their cause and evaluate the geographic extent of this variability one uncertainty in comparing marine geologic records of millennial scale variability is the extent to which mixing of sediment by organisms at the seafloor bioturbation may attenuate millennial scale events in the stratigraphic record evidence of attenuation of millennial variability can be found in cores with sedimentation rates in the range of 5 15 cm kyr modeling the attenuation of a hypothetical input time series similar to gisp2 using a moderate level of mixing provides estimates of attenuation as a function of sedimentation rate the amplitude of a 4 kyr duration event is reduced by 50 for sedimentation rates10 cm kyr and reduced by 20 for sedimentation rates of 20 cm kyr minimal attenuation 5 is achieved only when the sedimentation rate exceeds 50 cm kyr for a 4 kyr duration event and 70 cm kyr for a 2 kyr duration event the intensity of mixing plays a role in determining how much attenuation occurs the amplitude of a 4 kyr duration event in a 10 cm kyr core is reduced by 75 under strong mixing or reduced by 25 under weak mixing this study indicates that the original amplitude of dansgaard oeschger do millennial scale events observed during the last glacial may be twice the observed amplitude for cores with sedimentation rates 10 20 cm kyr that have experienced moderate bioturbation regional comparisons of the amplitude of millennial scale variability will require cores with weak mixing or sedimentation rates exceeding 50 cm kyr in order to avoid biased estimates of the amplitude of millennial scale 4 kyr duration variability

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

geochemical criteria for a refined tectonic discrimination of orogenic andesites abstract minor trace element and sr isotope data are compiled for tertiary recent orogenic andesites of three tectonic settings 1 oceanic island arcs divided into low k and other andesites 2 continental island arcs and thin continental margins and 3 thick continental margins andean from 1 to 3 there is a steady overlapping increase in la ce ree la yb la y th th u zr y hf yb and ni co and a decrease in k la p la sc cr and sc ni optimum discriminationis achieved with a plots of la yb vs th and la yb vs sc ni and b cluster analysis using the critical parameters listed above shoshonitic andesites and high mg andesites boninites are considered separately orogenic andesites are distinguished from non orogenic andesites by high contents of al low contents of ti zr ree y nb ta and ga and the absence of pronounced negative eu anomalies

varve calibrated records of carbonate and organic carbon accumulation over the last 2000 years in the black sea sedimentologic and geochemical studies of box and gravity cores recovered from the black sea during the first leg of a multileg international black sea expedition in 1988 allow reconstruction of the basinwide holocene environmental history of the black sea in the deeper parts of the basin box cores typically recovered a flocculent surface layer fluff laminated coccolith marls of unit i 25 45 cm thick and the upper 5 10 cm of finely laminated dark colored sapropels of unit ii fine grained homogeneous mud turbidites are interbedded with units i and ii over much of the basin but the stratigraphie position of these turbidites differs from site to site the deposition of individual turbidites up to 15 cm thick does not appear to have significantly disturbed underlying laminae sediment trap deployments in the black sea suggest that light and dark laminae couplets represent annual increments of sedimentation i e varves we have therefore constructed a varve chronology for the sequence in order to correlate and date distinctive sedimentation and paleoenvironmental events distinctive groups of laminae in unit i can be correlated across the entire deeper basin a distance of more than 1000 km this implies a remarkable homogeneity in production accumulation and preservation of biogenic material over much of the black sea during deposition of unit i the change from deposition of finely laminated organic carbon rich sapropels unit ii to laminated more calcareous coccolith rich marls unit i is thought to represent the crossing of a salinity threshold for emiliania huxleyi the varve chronology sets this change at about 1 63 ka 1633 100 yr b p but the record of magnetic secular variation measured in several cores produces an age estimate of about 2 0 ka for the base of unit i or about 1 2 times the varve age the average of six calibrated accelerator mass spectrometry radiocarbon ages for the base of unit i is 2 7 ka or about 1 7 times the varve age following the initial change to coccolith dominated sedimentation deposition of sapropel resumed for at least one significant period 1 56 1 25 ka since 1 25 ka cycles of carbonate deposition with quasi decadal periodicities have produced characteristic darker and lighter assemblages of laminae these cycles may have been climatically driven geochemical analyses coupled with the varve ages adopted herein indicate that accumulation rates of carbonate are nearly an order of magnitude higher in unit i averaging 35 45 g m 2 yr 1 than in sapropelic unit ii which contains primarily detrital carbonate the accumulation of lithogenic components in parts of unit i is only 1 5 times the rate in unit ii deepwater organic carbon accumulation rates are somewhat higher in unit i 3 5 4 5 g m 2 yr 1 than in the upper part of unit ii organic carbon accumulation rates in unit i are somewhat antithetic to those of carbonate and on the basis of this and additional constraints placed by pyrolysis and carbon isotopic analyses of organic material it appears that terrestrial organic matter is an important component perhaps 25 of total organic carbon burial in the basin unit i in the western part of the black sea has a higher terrestrial organic component and higher accumulation rates of terrigenous clastic material than unit i in the eastern part this difference between eastern and western black sea is to be expected because of the major rivers that empty into the western black sea from eastern europe ukraine and russia shallow slope sites but still within euxinic bottom waters have lower organic carbon accumulation rates and lower pyrolysis hydrogen indices than deepwater basinal sites suggesting selective resuspension and oxidation of organic matter at basin margins and focusing of organic matter deposition toward the basin center a comparison of the black sea data with those from several open ocean sites with similar water depths showed no significant difference between organic carbon accumulation rates under oxic and anoxic conditions for a given bulk accumulation rate the organic carbon accumulation rates normalized to primary productivity are about the same in both settings

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

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

the influence of oxic degradation on the sedimentary biomarker record ii evidence from arabian sea sediments abstract biomarker accumulation rates in nine different time slices in three cores on and at the foot of a submarine high in the northern arabian sea the murray ridge were measured to investigate the influence of oxygen exposure time on the preservation of biomarker signals in the sedimentary record all three sites experienced the same history of surface water productivity and sediment supply but had different bottom water redox conditions due to their different positions in just below well below relative to the present location of the intense oxygen minimum zone omz past variations in the intensity and position of the omz known from a wide variety of proxies toc content distribution and abundance of planktonic and benthic foraminifera and pteropods trace metals and 15 n enabled specific biomarker i e n alkanes steroids alkenones alkyldiols c 26 fatty acid loliolide biphytane diols and archaeal tetraether lipids accumulation rates at contrasting oxygen exposure times to be compared the results indicate that these accumulation rates can vary by more than an order of magnitude for marine biomarkers in addition there are significant differences in the degree of oxic degradation of different types of biomarkers terrestrial n alkanes are much more resistant than alkenones and n alkyl diols which are more refractory than steroids and biphytane diols these differences in degree of oxic degradation indicate that biomarker distributions will change on increasing exposure to oxygen these findings have a significant impact on the application of biomarkers to sedimentary settings in which oxygen exposure time is likely to change significantly

geodynamic and magmatic stages on a traverse through the andes between 20 and 24 s n chile s bolivia nw argentina metamorphic precambrian basement is exposed in the chilean pre cordillera in the form of a narrow horst and also in the argentinian puna miogeosynclinal pelites and psammites of devonian age dominate in the western part of the andes while early palaeozoic clastics occur in the e insignificant triassic sediments were followed by wide spread shallow marine jurassic deposition cretaceous and tertiary strata are predominantly terrestrial deposits whereas the precambrian and palaeozoic series were intensely deformed by folding block faulting dominates in the volcano sedimentary cover magmatic activity has been significant since the precambrian while s type intrusives and extrusives occurred mainly in the palaeozoic i type magmatic rocks predominated in the mesozoic the cenozoic volcanism in the cordillera occidental originated in the lower and upper crust magnetotelluric and seismic investigations on the traverse show extremely low electric resistivity values coinciding with a strong absorption of seismic waves below the chilean pre cordillera and the cordillera occidental this phenomenon can best be explained by the existence of partial melts at depths of more than 10 km the bouguer values decrease by about 430 mgal from the coast to the cordillera occidental in the precambrian and palaeozoic the continent apparently extended farther to the w the change from a passive to an active continental margin took place at the palaeozoic mesozoic boundary with the break up of pangea in order to grasp better the tectonic and magmatic evolution as well as the recent structure of the crust in the central andes a combined geological geophysical investigation has been made along a traverse through the andes between 20 and 24 s fig 1 the following pages present a review of the geological development together with the first results of work from the chilean section of the traverse

distribution and export of isoprenoid tetraether lipids in suspended particulate matter from the water column of the western atlantic ocean abstract the tex86 paleotemperature proxy is based on the distribution of archaeal glycerol dibiphytanyl glycerol tetraether gdgt lipids preserved in marine sediments yet both the influence of different physiological factors on the structural distribution of gdgts and the mechanism s by which gdgts is are exported to marine sediments remain s unresolved we investigated the abundance and structural distribution of gdgts in the south west and equatorial atlantic ocean in four water column profiles spanning 48 degrees of latitude the depth distribution was consistent with production by ammonia oxidizing thaumarchaeota maximum gdgt concentration occurred at the base of the no2 maximum core gdgts dominated the structural distribution in surface waters above the no2 maximum and intact polar gdgts potentially indicating live cells were more abundant below the no2 maximum between 0 and1000 m 98 of the integrated gdgt inventory was present in waters at and below the no2 maximum depth profiles of tex86 temperature values displayed local minima at the no2 maximum while the ratio of gdgt 2 gdgt 3 increased with depth a model based on the results predicts an average depth of origin for gdgts exported to sediments between ca 80 250 m in the model exported tex86 values are remarkably insensitive to change in the average depth of origin of gdgts however tex86 values exported from the water column appear to reflect euphotic zone productivity possibly due to the correlative intensity of organic matter remineralization providing substrates for ammonia oxidation predicting the influence of these regional controls on sedimentary tex86 records requires a better understanding of the interaction between gdgt production particle dynamics and the depth of origin for exported organic matter

bioturbational mixing depth and carbon flux at the seafloor radiocarbon dating series bulk sediment and organic carbon flux from various atlantic deep sea regions reveal that the thickness of the bioturbated zone increases by 2 cm if food supply increases by 1 gcm 2yr 1 r 0 8 bulk sediment accumulation rates do not influence the depth of bioturbational mixing under normal pelagic sedimentary conditions we believe that this relationship between nutrient supply and benthic mixing can be used for a quantitative and time variable unmixing procedure to improve high resolution stratigraphic correlations and paleoclimatic interpretations of deep sea records

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

early diagenetic remineralization of sedimentary organic c in the gulf of papua deltaic complex papua new guinea net loss of terrestrial c and diagenetic fractionation of c isotopes oceania supplies 40 of the global riverine flux of organic carbon approximately half of which is injected onto broad continental shelves and processed in shallow deltaic systems the gulf of papua on the south coast of the large island of new guinea is one such deltaic clinoform complex it receives 4 mt yr 1 particulate terrestrial organic carbon with initial particle corg loading 0 7 mg m 2 corg loading is reduced to 0 3 mg m 2 in the topset upper foreset zones of the delta despite additional inputs of mangrove and planktonic detritus and high net sediment accumulation rates of 1 4 cm yr 1 carbon isotopic analyses 13c 14c of co2 and corg demonstrate rapid 100 yr remineralization of both terrestrial 13c 28 6 and marine corg 13c 20 5 ranging in average age from modern bomb 14c 60 to 1000 yr 14c 140 efficient and rapid remineralization in the topset upper foreset zone is promoted by frequent physical reworking bioturbation exposure and reoxidation of deposits the seafloor in these regions particularly 20 m apparently functions as a periodically mixed suboxic batch reactor dominated by microbial biomass although terrestrial sources can be the primary metabolic substrates at inshore sites relatively young marine corg often preferentially dominates pore water co2 relative to bulk corg in the upper foreset thus a small quantity of young rapidly recycled marine organic material is often superimposed on a generally older less reactive terrestrial background whereas the pore water co2 reflects both rapidly cycled marine and terrestrial sources terrestrial material dominates the slower overall net loss of corg from particles in the topset upper foreset zone i e recycled marine corg leaves little residue preferential utilization of corg subpools and diagenetic fractionation of c isotopes supports the reactive continuum model as a conceptual basis for net decomposition kinetics early diagenetic fractionation of c isotopes relative to the bulk sedimentary corg composition can produce changes in 14c activity independent of radioactive decay in the gulf of papua topset upper foreset 14c of pore water co2 averaged 300 greater than corg sediment between 1 3 m depth in deposits diagenetic fractionation and decomposition aging of sedimentary corg compromises simple application of 14c for determination of sediment accumulation rates in diagenetically reactive 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

gdgt and alkenone flux in the northern gulf of mexico implications for the tex86 and uk 37 paleothermometers the tex86 and u37k molecular biomarker proxies have been broadly applied in downcore marine sediments to reconstruct past sea surface temperature sst although both tex86 and u37k have been interpreted as proxies for mean annual sst throughout the global ocean regional studies of glycerol dibiphytanyl glycerol tetraethers gdgts and alkenones in sinking particles are required to understand the influence of seasonality depth distribution and diagenesis on downcore variability we measure gdgt and alkenone flux as well as the tex86 and u37k indices in a 4 year sediment trap time series 2010 2014 in the northern gulf of mexico ngom and compare these data with core top sediments at the same location gdgt and alkenone fluxes do not show a consistent seasonal cycle however the largest flux peaks for both occurs in winter u37k covaries with sst over the 4 year sampling interval but the u37k sst relationship in this data set implies a smaller slope or nonlinearity at high temperatures when compared with existing calibrations furthermore the flux weighted u37k value from sinking particles is significantly lower than that of underlying core top sediments suggesting preferential diagenetic loss of the tri unsaturated alkenone in sediments tex86 does not covary with sst suggesting production in the subsurface upper water column the flux weighted mean tex86 matches that of core top sediments confirming that tex86 in the ngom reflects local planktonic production rather than allochthonous or in situ sedimentary production we explore potential sources of uncertainty in both proxies in the ngom but demonstrate that they show nearly identical trends in twentieth century sst despite these factors

iron oxide copper gold deposits an andean view iron oxide copper gold iocg deposits defined primarily by their elevated magnetite and or hematite contents constitute a broad ill defined clan related to a variety of tectono magmatic settings the youngest and therefore most readily understandable iocg belt is located in the coastal cordillera of northern chile and southern peru where it is part of a volcano plutonic arc of jurassic through early cretaceous age the arc is characterised by voluminous tholeiitic to calc alkaline plutonic complexes of gabbro through granodiorite composition and primitive mantle derived parentage major arc parallel fault systems developed in response to extension and transtension induced by subduction roll back at the retreating convergent margin the arc crust was attenuated and subjected to high heat flow iocg deposits share the arc with massive magnetite deposits the copper deficient end members of the iocg clan as well as with manto type copper and small porphyry copper deposits to create a distinctive metallogenic signature

volcanic dykes in the north chilean coast range dense swarms of predominantly mafic dykes outcrop in the north chilean coast range these rocks are not lamprophyres they mark channelways used by jurassic to lower cretaceous extrusives

high and low latitude climate control on the position of the southern peru chile current during the holocene 1 we reconstructed changes of temperature salinity and productivity within the southern peru chile current during the last 8000 years from a high resolution sediment core recovered at 41 s using alkenones isotope ratios of planktic foraminifera biogenic opal and organic carbon paleotemperatures and paleosalinities reached maximum values at 5500 years ago and thereafter declined to modern values whereas paleoproductivity continuously increased throughout the last 8000 years we ascribe these long term holocene trends primarily to latitudinal shifts of the antarctic circumpolar current acc the concurrence with shifts in the position of the southern westerlies points to a common response of atmospheric and oceanographic circulation patterns off southern chile millennial to centennial scale fluctuations of paleotemperatures and paleosalinities on the other hand lag displacements in the position of the southern westerlies but reveal a significant correlation to short term temperature changes in antarctica indicating a high latitude control of the acc at these timescales

large changes in seasonal sea ice distribution and productivity in the sea of okhotsk during the deglaciations changes in the surface environment of the central sea of okhotsk were reconstructed using tex86 paleothermometry facilitated by the bit index in order to investigate paleoenvironmental changes during the glacial interglacial cycles the core top tex86 derived temperature is the same as the present day summer sea surface temperature sst suggesting that tex86 records seasonal rather than annually averaged ssts in this region the tex86 record reveals 3 c lower summer sst during glacial maxima than during interglacial periods and significant warming during the deglaciations 15 10 ka and 136 130 ka this is consistent with previous inferences of more expanded and persistent seasonal sea ice during the glacial periods than the present day and its substantial retreat during the deglaciation timing of the deglacial warming also coincided with a distinct increase in coccolithophorid productivity suggesting a causal relationship between sea surface warming and coccolithophorid blooms during the deglaciations the relationship could reflect an increase in the supply of fresh and warm water from the amur river during deglaciation which significantly impacted hydrology by facilitating sea surface stratification which in turn promoted production of coccolithophids

low latitude climate control on sea surface temperatures recorded in the southern okinawa trough during the last 13 3 kyr abstract paleotemperature records were reconstructed for the past 13 3 kyr using the alkenone unsaturation index uk 37 and the tetraether index of 86 carbon atoms tex86 proxies measured in sediment core oki 151 which was collected in the southern okinawa trough the uk 37 and tex86 derived temperatures for the top sample are close to the modern mean annual sea surface temperature sst changes in ssts in the southern okinawa trough were primarily controlled by the western tropical pacific ocean low latitude winter insolation and sea level rise unlike previous studies we found that the high latitude north atlantic played no significant role in the sst variations in this area moreover ssts in the southern okinawa trough decoupled from the east asian summer monsoon system in the last 13 3 kyr the uk 37 and tex86 based ssts dropped significantly at 7 6 6 9 kyr bp centered on 7 3 kyr bp these findings suggest that the cold event at 7 3 kyr bp was widely recorded in the okinawa trough however the tex86 based ssts dropped approximately 14 c during this period for an unknown reason

comparison of eastern tropical pacific tex 86 and globigerinoides ruber mg ca derived sea surface temperatures insights from the holocene and last glacial maximum abstract the use of the tex 86 temperature proxy has thus far come to differing results as to whether tex 86 temperatures are representative of surface or subsurface conditions in addition although tex 86 temperatures might reflect sea surface temperatures based on core top holocene values this relationship might not hold further back in time here we investigate the tex 86 temperature proxy by comparing tex 86 temperatures to mg ca temperatures of multiple species of planktonic foraminifera for two sites in the eastern tropical pacific on the cocos and carnegie ridges across the holocene and last glacial maximum core top and holocene tex 86 h temperatures at both study regions agree well within error with the mg ca temperatures of globigerinoides ruber a surface dwelling planktonic foraminifera however during the last glacial maximum tex 86 h temperatures are more representative of upper thermocline temperatures and are offset from g ruber mg ca temperatures by 5 8 c and 2 9 c on the cocos ridge and carnegie ridge respectively this offset between proxies cannot be reconciled by using different tex 86 temperature calibrations and instead we suggest that the offset is due to a deeper export depth of gdgts at the lgm we also compare the degree of glacial cooling at both sites based on both temperature proxies and find that tex 86 h temperatures greatly overestimate glacial cooling especially on the cocos ridge this study has important implications for applying the tex 86 paleothermometer in the eastern tropical pacific

distribution of intact and core tetraether lipids in water column profiles of suspended particulate matter off cape blanc nw africa in the reconstruction of sea surface temperature sst from sedimentary archives secondary sources lateral transport and selective preservation are considered to be mainly negligible in terms of influencing the primary signal this is also true for the archaeal glycerol dialkyl glycerol tetraethers gdgts that form the basis for the tex86 sst proxy our samples represent four years variability on a transect off cape blanc nw africa we studied the subsurface production vertical and lateral transport of intact polar lipids and core gdgts in the water column at high vertical resolution on the basis of suspended particulate matter spm samples from the photic zone the subsurface oxygen minimum zone omz nepheloid layers nl and the water column between these furthermore we compared the water column spm gdgt composition with that in underlying surface sediments this is the first study that reports tex86 values from the precursor intact polar lipids ipls associated with specific head groups ipl specific tex86 we show a clear deviation from the sea surface gdgt composition in the omz between 300 and 600 m since neither lateral transport nor selective degradation provides a satisfactory explanation for the observed tex derived temperature profiles with a bias towards higher temperatures for both core and ipl specific tex86 values we suggest that subsurface in situ production of archaea with a distinct relationship between lipid biosynthesis and temperature is the responsible mechanism however in the nw african upwelling system the gdgt contribution of the omz to the surface sediments does not seem to affect the sedimentary tex86 as it shows no bias and still reflects the signal of the surface waters between 0 and 60 m

interferometric global positioning system three dimensional positioning source for airborne gravimetry the naval research laboratory nrl and the national geodetic survey recently collaborated on an experiment to test interferometric mode global positioning system gps tracking as a source of altitude and vertical acceleration for airborne gravity measurement reduction a texas instruments ti 4100 gps receiver and an extremely precise radar altimeter were installed in an nrl p 3 orion aircraft a second ti 4100 was located at a fixed base station of known location carrier phase data from four gps satellites were recorded from the fixed and airborne receivers and postprocessed to produce three dimensional displacements of the airborne station relative to the base station differences in gps and radar altimeter coordinate systems were modeled and removed the resulting gps and radar altitudes were compared the two unfiltered 1 hz data sets differed by an rms of 20 cm when aircraft dynamics were controlled by autopilot in straight and level flight during hand flown maneuvers such as turns climbs and descents rms differences varied from 40 to 80 cm a significant portion of the differences can be attributed to remaining coordinate system discrepancies and to uncompensated geometric effects due to aircraft motion we have also examined vertical acceleration time series produced by doubly differencing both data sets by applying a low pass filter which allows resolution of features with wavelengths of 20 km and greater at nominal aircraft speeds of 100 m s the rms difference between the radar and gps derived vertical accelerations was less than 2 mgal 2 10 5 m s2 during straight and level flight it should be possible to improve this accuracy and wavelength resolution with future improvements in measurement and processing techniques the results of this experiment show that the incorporation of interferometric mode gps tracking into the airborne gravity measurement system will make possible rapid and relatively inexpensive gravity surveys over any type of terrain while simultaneously providing accurate measurements of ground height profiles beneath the aircraft

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

bioturbation and holocene sediment accumulation fluxes in the north east atlantic ocean benthic boundary layer experiment sites bioturbation and holocene sediment accumulation are quantified in the three experimental areas of the benthic boundary layer benbo programme by means of the natural radionuclides 14c and 210pb and the artificial radionuclides 137cs and 241am the holocene accumulation rates determined by the radiocarbon method are 4 4 and 6 5 cm kyr 1 at sites b rockall plateau 1100 m water depth and c feni drift 1925 m water depth respectively accumulation at site a situated between feni drift and porcupine bank at 3570 m water depth was interrupted by an erosional event in the mid holocene which removed 0 25 m or more of the uppermost sediment present at that time the estimated accumulation rate since that event is 2 1 cm kyr 1 different estimates of surficial bioturbation mixing depths at site b are returned by the 210pbexcess and 14c methods with the former indicating 10 cm and the latter unusually deep at 17 cm at site c 210pbexcess and the fallout radionuclides 137cs and 241am are present in two distinctly separated depth zones with the deepest mixing down to 15 cm similar to the 14c mixed layer depth this is ascribed to deep burrowing by sipunculid or echiuran worms at site c and similar deep mixing is inferred to be necessary at site b to produce the differences in mixed layer depths derived from the longer and shorter lived radionuclide profiles although the deep burrowing episodes must be rare 1 event per 102 yr the greater accumulation rate at site c compared with site b is produced by an enhanced flux of current driven clay and silt sized material this fine material both dilutes the caco3 content of the site c sediment and is responsible for the higher corg content observed at site c compared with site b unlike the site b and c sediments which are fine grained the coarse 63 125 m size fraction is the most abundant size class in the late holocene sediments at site a suggesting that the sediments at this location are winnowed

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

hydrographic variability in the northern south china sea over the past 45 000 years new insights based on temperature reconstructions by uk 37 and texh86 proxies from a marine sediment core md972146 abstract millennial scale climate variability was persistent feature for greenland ice core and north atlantic marine records during the marine isotope stage mis 3 studying high quality climatic archives outside of the greenland and north atlantic with precise constraint of absolute dating and high resolution sampling is a prerequisite to understand how the millennial scale changes well expressed in north hemisphere nh high latitudes had been propagated out to the other regions here we generated the surface and subsurface hydrography u k 37 and tex h 86 temperatures and terrestrial material input n alkanes records with precise ams 14 c dated control for the 45 ka from a core md972146 retrieved from the northern south china sea scs then we compared our records to the oxygen isotope record from a greenland ngrip ice core and the mean grain size record from a loess sequence at gulang china we found that the millennial scale oscillations of hydrolography and terrestrial material inputs records during the time since the last deglaciation and of 33 45 ka share similar patterns in timing and amplitude of the nh high latitude climate however we found that a non nh pattern of millennial scale oscillations for the late mis 3 20 33 ka of our hydrography and terrestrial material inputs records our studies imply that the changes of obliquity also may be important in determining the timing and amplitude of millennial scale east asian monsoon eam variability expressed in the northern scs hydrography and terrestrial material inputs

verification of airborne positioning using global positioning system carrier phase measurements two experiments have been conducted to determine the accuracy with which an aircraft can be positioned in flight using carrier phase measurements from satellites of the navstar global positioning system gps in each experiment a photogrammetric camera was flown over a calibration area providing ground control that enabled aerotriangulation to be performed on ground targets or conversely for the camera position to be independently determined gps measurements were used to determine the position of an antenna located on the aircraft at the time of each photo and using the fixed antenna camera vector to determine the positions of the camera the gps derived camera positions were then used to compute the positions of the ground targets in an experiment in texas the differences between the conventional and gps based aerotriangulation display biases of 1 3 cm horizontally and 28 cm vertically and rms differences of about 2 cm 3 cm and 6 cm in north east and height respectively the camera positions derived from the aerotriangulation showed similar biases when compared to the gps derived camera positions and rms differences of about 7 cm in the horizontal and 9 cm in height because of edge effects in the photography the actual precision is slightly better a second experiment in washington revealed biases of several meters apparently due to unresolved coordinate system differences however a helmert transformation in this case produced rms differences between gps derived and photogrammetrically determined ground positions of 3 5 cm while these results demonstrate the need for care in relating gps results to other geodetic measurements they also show the great potential of gps carrier phase measurements for precise kinematic positioning and a variety of remote sensing applications

asynchronous alkenone and foraminifera records from the benguela upwelling system abstract radiocarbon stratigraphy is an essential tool for high resolution paleoceanographic studies age models based on radiocarbon ages of foraminifera are commonly applied to a wide range of geochemical studies including the investigation of temporal leads and lags the critical assumption is that temporal coupling between foraminifera and other sediment constituents including specific molecular organic compounds biomarkers of marine phytoplankton e g alkenones is maintained in the sediments to test this critical assumption in the benguela upwelling area we have determined radiocarbon ages of total c37 c39 alkenones in 20 samples from two gravity cores and three multicorer cores the cores were retrieved from the continental shelf and slope off namibia and samples were taken from holocene deglacial and last glacial maximum core sections the alkenone radiocarbon ages were compared to those of planktic foraminifera total organic carbon fatty acids and fine grained carbonates from the same samples interestingly the ages of alkenones were 1000 to 4500 yr older than those of foraminifera in all samples such age differences may be the result of different processes bioturbation associated with grain size effects lateral advection of recycled material and redeposition of sediment on upper continental slopes due to currents or tidal movement are examples for such processes based on the results of this study the age offsets between foraminifera and alkenones in sediments from the upper continental slope off namibia most probably do not result from particle selective bioturbation processes resuspension of organic particles in response to tidal movement of bottom waters with velocities up to 25 cm s recorded near the core sites is the more likely explanation our results imply that age control established using radiocarbon measurements of foraminifera may be inadequate for the interpretation of alkenone based proxy data observed temporal leads and lags between foraminifera based data and data derived from alkenone measurements may therefore be secondary signals i e the result of processes associated with particle settling and biological activity

in coherent multiproxy signals in marine sediments implications for high resolution paleoclimate reconstruction abstract accurate chronologies are the backbone of paleoclimate research yet for marine sedimentary records the same age model is often applied to co eval components that may have experienced different pre depositional histories leading to aliasing in corresponding proxy signals here we demonstrate 14c age discrepancies among several proxy carriers and use them to highlight spatio temporal disparities among different components of the sediment total organic carbon toc alkenones and alkanoic fatty acids have older ages than co occurring planktonic foraminifera in corresponding depth intervals of a sediment core retrieved from the so called shackleton sites on the southwest iberian margin off portugal temporal differences are explained by the addition of pre aged material that is transported to the site by lateral advection rivers or wind we then modeled the age structure and relative abundance of the different pools that might have contributed to the older ages of toc and alkenones results suggest the addition of a moderate 15 20 proportion of very old allochthonous material 18 500 49 900 yr this information was used to deconvolve the alkenone derived sea surface temperature sst record and assess the impact of allochthonous inputs on paleoclimate signals

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

constraining the applicability of organic paleotemperature proxies for the last 90 myrs abstract we evaluated changes in the distributions of long chain alkenones long chain diols and gdgts lipids commonly used for paleothermometry over the last 90 myrs for sediments deposited on the new jersey shelf the bass river site and assessed potential effects of different ancestral producers and diagenesis on their distributions and their impact on the associated temperature proxies as reported before the paleogene distributions of alkenones are generally similar to those in modern haptophytes but unusual alkenone distributions characterized by a dominant di unsaturated c40 alkenone are observed for late cretaceous sediments suggesting different ancestral source organisms for alkenones in this interval the isoprenoid gdgt distributions remained comparable to modern day distributions suggesting that tex86 can be applied up to ca 90 ma the miocene long chain diol distributions are similar to modern day distributions but the older sediments reveal unusual distributions dominated by the c28 1 12 and c26 1 13 diols suggesting different source organisms before 30 ma accordingly the ldi does not match other paleotemperature proxies suggesting its applicability might be compromised for sediments older than the miocene our results indicate that of the three proxies the tex86 seems to be the most applicable for deep time temperature reconstructions

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

composition age and provenance of organic matter in nw african dust over the atlantic ocean 1 eolian dust deposited on a meteorology buoy over the boreal winter and spring of 1992 1993 in the northeast atlantic off northwest africa 18 n 22 w afforded sufficient material for detailed assessment of its biogeochemical characteristics and provenance the sample was subjected to microscopic examination and bulk elemental isotopic black carbon and molecular lignin lipid analyses the bulk elemental composition and organic carbon oc content 1 02 dry weight establishes the dust s origin as continental upper crust and is typical of dusts that emanate from west africa these data are in accord with the extensive satellite imagery documenting the transit of dust clouds from the sahara and sahel regions e g nasa toms aerosol index microscopic examination reveals that charcoal like particles from vegetation fires black carbon bc are the most abundant morphologically distinct organic components accelerator mass spectrometry ams 14c analysis yields conventional 14c ages for bulk oc of 1260 40 years and bc of 2070 35 years taken together with corresponding stable carbon isotopic compositions 13c 18 9 and 15 1 respectively these results suggest the presence of biomass and burning residues derived from predominantly c4 vegetation that accumulated in soils over the late holocene molecular level measurements are also consistent with this scenario for example lignin derived phenols in the dustfall sample indicate a significant contribution of angiosperm grass type tissue the altered nature of the lignin suggests storage as residues in soils solvent extractable lipid constituents include a marked leaf wax type component with a molecular and stable carbon isotopic composition similar to those observed in surface marine sediments in this region the hydrocarbon fraction contained some diesel type contamination but the n alkanes c23 c33 retained a prominent odd even distribution with 13c ranging from 26 7 to 28 5 the suite of even carbon numbered n alkanols c22 c32 is 14c dated at 647 150 years with 13c values ranging from 23 9 to 30 4 the long chain n alkanoic acids c22 c32 exhibited 13c values ranging from 22 6 to 27 4 these waxes are evidently a mixed signal derived from contemporary c3 and c4 vegetation and from ablated soils and desiccated lake sediments of middle to late holocene age this molecular approach shows promise as a tool for continental paleoenvironmental assessment particularly with respect to past vegetation cover regional aridity and wind systems

advances in aerogeophysics and precise positioning gravity topography and high resolution applications airborne magnetic surveys have long been a primary tool for geologic mapping resource exploration hazard evaluation and tectonic studies recent advances in precise positioning have enabled other geophysical tools such as laser and radar altimeters and the gravity meter to be mounted on airplanes and contribute to geologic and environmental studies the principal advantages of airborne geophysical surveys over ground based studies result from enhanced experiment design including improved access to remote and contaminated areas optimized sampling rapid sampling rate and tremendous potential for interdisciplinary studies

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

molecular proxies for paleoclimatology we summarize the applications of molecular proxies in paleoclimatology marine molecular records especially are proving to be of value but certain environmentally persistent compounds can also be measured in lake sediments loess deposits and ice cores the fundamentals of this approach are the molecular parameters the compound abundances and carbon hydrogen nitrogen and oxygen isotopic contents which can be derived by the analysis of sediment extracts these afford proxy measures which can be interpreted in terms of the conditions which control climate and also reflect its operation we discuss two types of proxy those of terrigenous and those of aquatic origin and exemplify their application in the study of marine sediments through the medium of ten case studies based in the atlantic mediterranean and pacific oceans and in antarctica the studies are mainly for periods in the present the holocene and particularly the last glacial interglacial but they also include one study from the cretaceous the terrigenous proxies which are measures of continental vegetation are based on higher plant leaf wax compounds i e long chain circa c30 hydrocarbons alcohols and acids they register the relative contributions of c3 vs c4 type plants to the vegetation in the source areas the two marine proxies are measures of sea surface temperatures sst the longer established one u37k is based on the relative abundances of c37 alkenones photosynthesized by unicellular algae members of the haptophyta the newest proxy tex86 is based on c86 glycerol tetraethers gdgts synthesized in the water column by some of the archaeal microbiota the crenarchaeota

diagenetic and sedimentological controls on the composition of organic matter preserved in california borderland basin sediments compound specific radiocarbon 14c contents stable carbon isotopes and abundances of phytoplankton and vascular plant derived lipid biomarkers alkenones and fatty acids were obtained from santa barbara basin and santa monica basin sediments along with radiocarbon contents of planktic foraminifera and total organic carbon we investigated core top and prebomb sediment intervals at sites from the flanks and depocenters of the basins deposited under contrasting bottom water oxygen concentrations bulk organic matter generally has the lowest radiocarbon levels of all sediment constituents measured whereas planktic foraminifera tend to be the most radiocarbon enriched alkenones are systematically depleted in radiocarbon with respect to foraminifera short chain c14 c 16 c 18 fatty acids decrease rapidly in absolute abundance and relative to longer chain c24 homologues from core top to prebomb samples the loss of short chain fatty acids with depth is associated with 13c depletion of short chain fatty acids indicating preferential preservation of terrestrially derived fatty acids short chain fatty acids tend to be more 14c enriched relative to alkenones in core top sediments whereas longerchain homologues are generally the most radiocarbon depleted of the lipids studied here less refractory compounds e g short chain fatty acids are thus enriched in radiocarbon with respect to more recalcitrant biomarkers alkenones long chain fatty acids the lower 14c content of more refractory compounds reflects a larger proportion of laterally supplied preaged material greater preservation of labile organic compounds observed at the depocenters than in flank sediments results in the presence of younger biomarkers underlining the important influence of selective degradation of labile compounds on their radiocarbon ages

appraisal of tex86 and tex86l thermometries in subpolar and polar regions tex86 tetraether index of tetraethers consisting of 86 carbon atoms is a sea surface temperature sst proxy based on the distribution of archaeal isoprenoid glycerol dialkyl glycerol tetraethers gdgts in this study we appraise the applicability of tex86 and view the mathml sourcetex86l in subpolar and polar regions using surface sediments we present tex86 and view the mathml sourcetex86l data from 160 surface sediment samples collected in the arctic the southern ocean and the north pacific most of the sst estimates derived from both tex86 and view the mathml sourcetex86l are anomalously high in the arctic especially in the vicinity of siberian river mouths and the sea ice margin plausibly due to additional archaeal contributions linked to terrigenous input we found unusual gdgt distributions at five sites in the north pacific high gdgt 0 crenarchaeol and gdgt 2 crenarchaeol ratios at these sites suggest a substantial contribution of methanogenic and or methanotrophic archaea to the sedimentary gdgt pool here apart from these anomalous findings tex86 and view the mathml sourcetex86l values in the surface sediments from the southern ocean and the north pacific do usually vary with overlaying ssts in these regions the sedimentary tex86 sst relationship is similar to the global calibration and the derived temperature estimates agree well with overlaying annual mean ssts at the sites however there is a systematic offset between the regional view the mathml sourcetex86l sst relationships and the global calibration at these sites temperature estimates based on the global view the mathml sourcetex86l calibration are closer to summer ssts than annual mean ssts this finding suggests that in these subpolar settings a regional view the mathml sourcetex86l calibration may be a more suitable equation for temperature reconstruction than the global calibration

topographic mapping using radar interferometry processing techniques a new processing algorithm for the nasa jpl topsar topographic radar mapper is described it incorporates extensive motion compensation features as well as accurate three dimensional target location algorithm the processor applies an algorithm to resolving the absolute phase ambiguity this allows rectified height maps to be generated without any use of ground reference points the processor was tested using data acquired with extreme aircraft motion so that performance could be evaluated under adverse conditions the topographic maps generated by the radar were compared to digital elevation models dems derived using conventional optical stereo techniques in one region the rms elevation deviations measured were less than the specified dem accuracy and in the region covered by the more accurate dem errors varied from 2 2 m rms in relatively flat terrain up to 5 0 m in mountainous area the rms difference between radar and dem elevation over the 6 5 km by 22 km area covered by the more accurate dem was 3 6 m

the plutonism in the north chilean coast range and its geodynamic significance extended deep plutons of the chilean coast range can according to their composition age and spatial distribution be assigned to the following three superunits each of which represents a closed magmatic cycle albayay superunit approximately 300 200 m a cifuncho superunit approximately 190 130 m a esmeralda superunit less than 130 m a

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

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

selective aerobic and anaerobic degradation of lipids and palynomorphs in the eastern mediterranean since the onset of sapropel s1 deposition abstract selective degradation of organic matter in sediments is important for reconstructing past environments and understanding the carbon cycle here we report on compositional changes between and within lipid classes and kerogen types represented by palynomorph groups in relation to the organic matter flux to the sea floor and oxidation state of the sediments since the early holocene for central eastern mediterranean site abc26 this includes the initially oxic but nowadays anoxic presapropelic interval the still unoxidised lower part of the organic rich s1 sapropel its postdepositionally oxidised and nowadays organic poor upper part as well as the overlying postsapropelic sediments which have always been oxic a general 2 3 times increase in terrestrial and marine input during sapropel formation is estimated on the basis of the total organic carbon toc pollen spore dinoflagellate cyst n alkane n alkanol and n alkanoic acid concentration changes in the unoxidised part of the sapropel the long chain alkenones 1 15 diols and keto ols loliolides and sterols indicate that some plankton groups notably dinoflagellates may have increased much more apart from the terrestrial and surface water contributions to the sedimentary organic matter anomalous distributions and preservation of some c 23 c 27 alkanes alkanols and alkanoic acids have been observed which are interpreted as a contribution by organisms living in situ comparison of the unoxidised s1 sapropel with the overlying oxidised sapropel and the organic matter concentration profiles in the oxidised postsapropelic sediments demonstrates strong and highly selective aerobic degradation of lipids and palynomorphs there seems to be a fundamental difference in degradation kinetics between lipids and pollen which may be possibly related with the absence of sorptive preservation as a protective mechanism for palynomorph degradation the n alkanes impagidinium and nematosphaeropsis are clearly more resistant than toc the n alkanols and n carboxylic acids are about equally resistant whereas the pollen all other dinoflagellate cysts and other lipids appear to degrade considerably faster which questions the practice of normalising to toc without taking diagenesis into account selective degradation also modifies the relative distributions within lipid classes whereby the longer chain alkanes alcohols and fatty acids disappear faster than their shorter chain equivalents accordingly interpretation of lipid and palynomorph assemblages in terms of pre or syndepositional environmental change should be done carefully when proper knowledge of the postdepositional preservation history is absent two lipid based preservation proxies are tested the diol keto ol oxidation index based on the 1 15c 30 diol and keto ols doxi and the alcohol preservation index api whereby the former seems to be the most promising

surface area control of organic carbon accumulation in continental shelf sediments the relationship between organic carbon oc and grain size found in most continental shelf sediments is here reinterpreted in terms of the surface area of the sediments cores from many north american shelf environments show downcore decreases in oc to similar refractory background concentrations if expressed relative to the surface area of the sediments this consistent concentration is 0 86 mg oc m 2 which is equivalent in concentration to a monolayer of organic matter coating all mineral surfaces a more global collection of sediment water interface samples show that this relationship is even more extensive with exceptions occurring in areas of very high riverine sediment input organic pollution or low oxygen water columns density separations indicate that organic matter is largely adsorbed to mineral grains the microtopography of surfaces was examined with n2 sorption and most surface area was found to be inside pores of 10 nm width these data lead to a hypothesis that organic matter is protected by its location inside pores too small to allow functioning of the hydrolytic enzymes necessary for organic matter decay such protection would likely work in concert with other protection mechanisms such as humification this consistent surface area correlation with oc concentration may explain control of spatial and temporal variations in oc burial rates by sedimentation rates the pore protection hypothesis provides a causal mechanism for this observed control

an evaluation of 14c age relationships between co occurring foraminifera alkenones and total organic carbon in continental margin sediments 1 radiocarbon age relationships between co occurring planktic foraminifera alkenones and total organic carbon in sediments from the continental margins of southern chile northwest africa and the south china sea were compared with published results from the namibian margin age relationships between the sediment components are site specific and relatively constant over time similar to the namibian slope where alkenones have been reported to be 1000 4500 years older than co occurring foraminifera alkenones were significantly similar to 1000 years older than co occurring foraminifera in the chilean margin sediments in contrast alkenones and foraminifera were of similar age within 2 sigma error or better in the nw african and south china sea sediments total organic matter and alkenone ages were similar off namibia age difference toc alkenones 200 700 years chile 100 450 years and nw africa 360 770 years suggesting minor contributions of preaged terrigenous material in the south china sea total organic carbon is significantly 2000 3000 years older owing to greater inputs of preaged terrigenous material age offsets between alkenones and planktic foraminifera are attributed to lateral advection of organic matter physical characteristics of the depositional setting such as seafloor morphology shelf width and sediment composition may control the age of co occurring sediment components in particular offsets between alkenones and foraminifera appear to be greatest in deposition centers in morphologic depressions aging of organic matter is promoted by transport age offsets are correlated with organic richness suggesting that formation of organic aggregates is a key process