comparison of water column co2aq with sedimentary alkenone based estimates a test of the alkenone co2 proxy 1 the stable carbon isotopic compositions of alkenones have been used to interpret the long term history of the partial pressure of atmospheric carbon dioxide pco2 although extensive water column and culture studies document the potential utility and limitations of this approach to date the accuracy of pco2 values derived from sedimentary alkenones remains untested for this study we establish holocene aged alkenone based co2aq estimates co2aq alk from 20 sites along a central pacific ocean transect and compare them against both observed modern water column co2aq and estimated preindustrial concentrations at the depth of alkenone production at each site although the co2aq alk track measured water column values they are conspicuously lower than modern values across the subtropics this offset likely reflects the contributions of anthropogenic co2 in modern surface waters relative to preindustrial concentrations at the time of alkenone production when a model based estimate of anthropogenic co2 is removed from the modern observed values a majority 84 of co2aq alk falls within 20 of modeled preindustrial values consistency between the modeled and alkenone based estimates of preindustrial co2 levels points to the relative accuracy of the alkenone co2 method across a wide range of ocean and biogeographic regimes provided that phosphate concentrations at the depth of haptophyte production are reasonably constrained it further suggests that light limited growth and or active carbon uptake if they occur have a negligible effect on reconstructed co2aq

cooling trend over the past 4 centuries in northeastern hong kong waters as revealed by alkenone derived sst records abstract the climate history over the past few centuries is important to be used to assess how regional climate responds to global forcing here we report three high resolution alkenone based sea surface temperature sst records over the past 4 centuries from three sediment cores collected in the mirs bay northeastern hong kong all three sst records consistently show a general cooling trend toward the present with most of cooling occurring over the last century alkenone derived sst values stayed around 26 5 27 c at the three sites prior to 1900s and decreased into the range of 25 26 c the magnitude of cooling approximately from the little ice age lia to present tends to be dampened from 2 c nearshore to 1 c offshore the cooling trend as identified in all three sst records is thus opposite to the global temperature rise over the last century assisted with modern observations we interpret that the alkenone derived sst reflects increasing upwelling in the mirs bay which likely results from the strengthened east asian summer monsoon in the context of global warming over the last century

pronounced zonal heterogeneity in eocene southern high latitude sea surface temperatures paleoclimate studies suggest that increased global warmth during the eocene epoch was greatly amplified at high latitudes a state that climate models cannot fully reproduce however proxy estimates of eocene near antarctic sea surface temperatures ssts have produced widely divergent results at similar latitudes with ssts above 20 c in the southwest pacific contrasting with ssts between 5 and 15 c in the south atlantic validation of this zonal temperature difference has been impeded by uncertainties inherent to the individual paleotemperature proxies applied at these sites here we present multiproxy data from seymour island near the antarctic peninsula that provides well constrained evidence for annual ssts of 10 17 c 1 sd during the middle and late eocene comparison of the same paleotemperature proxy at seymour island and at the east tasman plateau indicate the presence of a large and consistent middle to late eocene sst gradient of 7 c between these two sites located at similar paleolatitudes intermediate complexity climate model simulations suggest that enhanced oceanic heat transport in the south pacific driven by deep water formation in the ross sea was largely responsible for the observed sst gradient these results indicate that very warm ssts in excess of 18 c did not extend uniformly across the eocene southern high latitudes and suggest that thermohaline circulation may partially control the distribution of high latitude ocean temperatures in greenhouse climates the pronounced zonal sst heterogeneity evident in the eocene cautions against inferring past meridional temperature gradients using spatially limited data within given latitudinal bands

proxy dependence of the temporal pattern of deglacial warming in the tropical south china sea toward resolving seasonality abstract sea surface temperatures ssts reconstructed from two globigerinoides ruber white morphotypes g ruber sensu stricto s s g ruber sensu lato s l mg ca and alkenones uk 37 from core md01 2390 from the tropical south china sea scs during the last deglaciation reveal a proxy dependent discrepancy in the temporal pattern of the deglacial warming alkenone data suggest that the deglacial warming is punctuated by a decrease in temperature between 17 and 15 ka bp corroborating previously published alkenone uk 37 sst records from the southern scs within dating uncertainties this cooling is coeval with the heinrich event 1 h1 time interval in the north atlantic region underscoring the imprints of northern hemisphere forcing on tropical scs ocean temperatures the deglacial uk 37 sst minimum is also paralleled by a maximum in g ruber morphotype specific 18o g ruber mg ca sst estimates suggest a morphotype specific record of ssts during the time interval of h1 whereas g ruber s s imply a continuous warming starting around 18 ka bp without any marked response to h1 g ruber s l based mg ca sst estimates reveal a cooling around 17 15 ka bp similar to the h1 interval cooling seen in the alkenone sst record similar proxy dependent differences in deglacial surface water warming have been recorded in the eastern equatorial pacific implying a common pattern on both sides of the tropical pacific ocean we submit that this discrepancy could be due to differences in seasonality of planktonic foraminifera g ruber morphotypes and alkenone producing algae

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

patterns of deglacial warming in the pacific ocean a review with emphasis on the time interval of heinrich event 1 abstract based on a compilation of currently available records of past sea surface temperature sst variability estimated from a variety of different proxies the regional scale deglacial sst development in the pacific ocean is tentatively classified into four endmember types the subtropical and tropical pacific is characterized by a continuous deglacial warming without marked interruption during the time interval of heinrich event 1 h1 whereas the subarctic north pacific exhibits centennial scale warm cold oscillations during this time interval sst records from marginal seas of the pacific show a deglacial warming interrupted by a cooling event coeval with h1 followed by a marked bolling sst increase a single sst record from the southwestern subantarctic pacific displays a continuous deglacial warming across h1 followed by an antarctic cold reversal type cooling during the allerod thus in contrast to the deglacial sst development in the atlantic which has been inferred to be overwhelmingly driven by the redistribution of heat through changes in the meridional overturning circulation moc none of the open oceanic pacific sst records reviewed here displays any obvious and or dominant response to the reduction of the moc and or the reorganization of atmospheric circulation during h1 within the limits of absolute chronologies all tropical and subtropical pacific sst records show an onset of deglacial warming at 19 1 ka coeval with the onset of the deglacial rise in sea level

molecular carbon isotopic fractionation of algal lipids during decomposition in natural oxic and anoxic seawaters abstract to evaluate molecular carbon isotopic fractionation of algal lipids during oxic and anoxic degradation emiliania huxleyi a marine haptophyte was incubated in seawater collected from two depths 30 and 930 m in the cariaco basin three classes of algal lipids alkenones fatty acids and sterols showed a degradation pattern characterized by complete loss in oxic seawater within 2 3 months the only exception was 16 0 fatty acid but 10 40 of initial algal lipids remained in the anoxic seawater after 3 months incubation oxic degradation rate constants of alkenones and fatty acids were generally 2 3 times higher than those derived from anoxic incubations however two sterols had similar degradation rate constants in oxic and anoxic seawater there was little preferential degradation of 37 3 relative to 37 2 alkenone in oxic and anoxic seawater leading to insignificant changes for u 37 k paleotemperature indicator in spite of alkenone degradation during oxic and anoxic degradation the same three classes of algal lipids exhibited different patterns of molecular carbon isotopic fractionation depletion 4 to 6 relative to initial value in 13 c for alkenones enrichment 2 to 7 relative to initial value for fatty acids and no change for sterols we postulate that the contrasting molecular isotopic fractionation patterns which depend on the structure of the lipid compounds are likely caused by different degradation reactions at specific functional groups where the carbon atoms may have dissimilar isotopic ratios from other carbon atoms in the molecules due to the differences in original precursors and synthesis pathways laboratory observation of these patterns of lipid fractionations during decomposition of a single phytoplankton material suggests that diagenetic processes can alter the molecular isotopic signals of preserved organic matter in a variety of ways

alkenones alkenoates and organic matter in coastal environments of nw scotland assessment of potential application for sea level reconstruction reconstruction of late quaternary sea level history in areas of glacioisostatic uplift often relies on sediment archives from coastal isolation basins natural coastal rock depressions previously isolated from or connected to the sea at different times proxy indicators for marine brackish or lacustrine conditions combined with precise dating can constrain the time when the sea crossed the sill threshold and isolated or connected the basin the utility of isolation basins in investigations of sea level change is well known but investigations have been mostly limited to microfossil proxies the application of which can be limited by preservation and nonanalog problems here we investigate the potential of long chain alkenones alkenoates and bulk organic parameters toc corg n for reconstructing past sea level changes in isolation basins in nw scotland we analyze organic biomarkers and bulk parameters from both modern basins at different stages of isolation from the sea and fossil basins with sea level histories reconstructed from established proxies logit regression analysis was employed to find which of the biomarker metrics or bulk organic measurements could reliably characterize the sediment samples in terms of a marine brackish or isolated lacustrine origin the results suggested a good efficiency for the alkenone index c37 4 at predicting the depositional origin of the sediments this study suggests that alkenones could be used as a novel proxy for sea level change in fossil isolation basins especially when microfossil preservation is poor

molecular stratigraphy of the santa barbara basin comparison with historical records of annual climate change abstract the molecular record of 20th century climatic variability in laminated sediments of the santa barbara basin has been compiled distributions and abundance profiles of alkenones and selected sterols reveal annual oscillations in sea surface temperatures and phytoplankton productivity positive excursions in alkenone temperature profiles coincide with all major 20th century el nino events recording oceanic warming downcore abundance profiles for dinosterol brassicasterol cholesterol and alkenones reflect productivity trends in phytoplankton and illustrate the comparative resilience of their molecular records series of subsurface concentration maxima for dinosterol a dinoflagellate derived sterol appear synchronous with regional historical reports of dinoflagellate blooms

molecular records of twentieth century el nino events in laminated sediments from the santa barbara basin organic molecules preserved in sediments especially long chain alkenones can preserve and record evidence of past climate variations1 5 a dependence of alkenone distributions on temperature has been recognized in cultures of the unicellular coccolithophorid alga emiliania huxleyi1 6 which survives in sediments and water column participates6 through this dependence stratigraphic profiles of the degree of alkenone unsaturation expressed asuk37 values1 have been shown in several oceanic settings to reflect long term changes in sea surface temperatures associated with glacial interglacial cycles1 5 here we show that annual variations in alkenone unsaturation in laminated sediments from the santa barbara basin off the shore of california reveal increases in water temperatures which can be linked directly to the observed sequence of el nino events in the twentieth century7 the range and variations in water temperatures calculated from uk37 values 12 8 15 2 c using the relationship established from culture experiments6 8 broadly correspond to the annually averaged temperatures 11 3 15 2 c measured intermittently by the calcofi programme at 20 m depth between 1953 and 1984 these results show that in favourable settings alkenone unsaturation profiles can provide an annually resolved record of oceanic temperaturechanges and may constitute a valuable tool for describing and evaluating the history of global climate variability and change

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

interhemispheric synchrony of the last deglaciation inferred from alkenone palaeothermometry the relative timings of the last deglacial warming in the southern and northern hemispheres are not well constrained but are a crucial component in understanding the mechanisms of deglaciation1 a clearer picture of the degree of interhemispheric synchrony has been obscured by a dearth of high resolution temperature records that can be tied to the absolute calendar timescale moreover the quantification of tropical temperatures during the last glacial cycle is controversial2 8 here we apply the alkenone method of sea surface temperature reconstruction9 10 to several high resolution sediment cores recovered from the tropical indian ocean between 20 n and 20 s the inferred initial sea surface temperature warming 15 000 calendar years ago at 20 s is in phase with northern hemisphere sea this study and air11 temperature changes but lags antarctic warming12 14 by several millennia this finding along with the results of recent modelling studies15 16 provides strong support for the idea that changes in the ocean s global thermohaline circulation were not the only cause of interhemispheric climate teleconnection during the last deglaciation

the role of uncertainty in estimating lead lag relationships in marine sedimentary archives a case study from the tropical pacific understanding the mechanisms behind any changes in the climate system often requires establishing the timing of events imprinted on the geological record however these proxy records are prone to large uncertainties which may preclude meaningful conclusions about the relative timing of events in this study we put forth a framework to estimate the uncertainty in phase relationships inferred from marine sedimentary records the novelty of our method lies in the accounting of the various sources of uncertainty inherent to paleoclimate reconstruction and timing analysis specifically we use a monte carlo process allowing sampling of possible realizations of the time series as functions of uncertainties in time the climate proxy and the identification of the termination timing we then apply this technique to 15 published sea surface temperature records from the equatorial pacific to evaluate whether we observed any significant changes in the termination timing between the east and the west we find that the uncertainty on the relative timing estimates is on the order of several thousand years and mainly stems from age model uncertainty 90 however even small differences in mean termination timings can be detected with a sufficiently large number of samples improvements in the dating of sediment records provide an opportunity to reduce uncertainty in studies of this kind

no moho uplift below the baikal rift zone evidence from a seismic refraction profile across southern lake baikal 1 the late cenozoic baikal rift zone brz in southern siberia is composed of several individual topographic depressions and half grabens with the deep lake baikal at its center we have modeled the seismic velocity structure of the crust and uppermost mantle along a 360 km long profile of the baikal explosion seismic transects best project across the rift zone in the southern part of lake baikal the seismic velocity structure along the profile is determined by tomographic inversion of first arrival times and 2 d ray tracing of first arrivals and reflections the velocity model shows a gently deepening moho from the siberian platform 41 km depth into the sayan baikal fold belt 46 km depth we can exclude the presence of any moho uplift around the 10 km deep sedimentary graben structure of southern lake baikal the lower crust includes a distinct 50 80 km wide high velocity anomaly 7 4 7 6 0 2 km s slightly offset to the northeast from the rift axis we interpret this feature as resulting from mafic intrusions their presence may explain the flat moho by compensation of lower crustal thinning by intrusion of mafic melts the pn wave velocities 8 15 8 2 km s are normal for the area and do not show any sign of decompression melting in the sub moho mantle such that possible lithosphere thinning has not reached the base of the crust on the basis of the results of the best project we suggest that the brz is formed by passive rifting in the rheologically weak suture between the siberian platform and the amurian plate

ecological and environmental factors affecting alkenone distributions in seawater and sediments 1 the use of alkenones to estimate past sea surface temperatures has gained wide acceptance but there are still some issues that need to be resolved before alkenone proxies can be used confidently in all environmental settings a particular concern is defining what seawater temperature is recorded by the alkenone distributions preserved in sediments does it for example reflect a seasonal average or a snapshot of bloom conditions or some other combination of environmental effects this paper reviews some of the environmental and ecological factors that might affect alkenone distributions and in particular the influence of depth and seasonality on alkenone production in the water column

composition of organic matter in subducted and unsubducted sediments off the nicoya peninsula costa rica odp leg 170 sites 1039 and 1040 investigation of sediment samples from sites 1039 and 1040 odp leg 170 drilled oa the nicoya peninsula costa rica by organic geochemical and organic petrological methods has revealed that subduction has only little influence on the composition of the sedimentary organic matter organic carbon contents reached 1 5 in the pleistocene samples but miocene and pliocene sediments had an average organic carbon content of less than 0 5 organic carbon sulfur ratios are generally below 2 8 reflecting an intense sulfate reduction in the uppermost sediments which was enhanced by sulfate supply both from sea water and deeper strata microscopical examinations indicate that the organic matter is mainly derived from marine sources a small amount of terrigenous organic matter is however present as well according to n alkane and fatty acid distributions the alkenone unsaturation index u k 0 37 shows only a slight decrease during the miocene and pliocene and stronger variations in the pleistocene probably indicating more stable sea surface temperatures during the miocene and pliocene variations in the pleistocene can possibly be related to glacial interglacial changes 2000 elsevier science ltd all rights reserved

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

an alkenone u 37 k quasi annual sea surface temperature record a d 1440 to 1940 using varved sediments from the santa barbara basin abstract analyses for c37 alkenones u37k and total organic carbon toc in a varved core from the depocenter of the santa barbara basin 34 13 5 n 120 01 w 590 m water depth have been made on an approximately 1 2 year basis from a d 1440 to 1940 the u37k based sea surface temperature sst record oscillates around 15 5 c with an amplitude of less than 3 c at approximately interannual decadal and centennial frequencies historical el nino southern oscillation enso events are matched only partially by warmer u37k ssts three records our sst a published pacific coral 18o and a published tree ring temperature anomaly from the california valleys show no evidence of colder temperatures during the little ice age ca 1500 to 1840 a d significantly there is a strong centennial scale cyclicity in the u37k sst record which approaches 1 c in amplitude toc burial and alkenone fluxes are largely controlled by sedimentation rate as expressed in varve thickness

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

the little ice age and medieval warm period in the sargasso sea sea surface temperature sst salinity and flux of terrigenous material oscillated on millennial time scales in the pleistocene north atlantic but there are few records of holocene variability because of high rates of sediment accumulation holocene oscillations are well documented in the northern sargasso sea results from a radiocarbondated box core show that sst was approximately 1 degree c cooler than today approximately 400 years ago the little ice age and 1700 years ago and approximately 1 degree c warmer than today 1000 years ago the medieval warm period thus at least some of the warming since the little ice age appears to be part of a natural oscillation 39 refs 4 figs 1 tab

alkenone temperature and carbon isotope records temporal resolution offsets and regionality 1 over the last decade the number of paleoceanographic studies presenting and discussing alkenone derived sea surface temperature sst records and carbon isotope ratios of alkenones 13calkenones has increased rapidly this short review paper summarizes the state of knowledge about sst variability determined by alkenone paleothermometry in sediment trap studies and investigations of marine sediments for timescales of single to millions of years in particular from the evaluation of quaternary records characteristic temperature pattern have emerged that mismatch with sst curves estimated by other methods e g foraminiferal stable oxygen isotopes and transfer functions in future studies the spatial distribution of such variance patterns typically observed in alkenone sst curves should be checked in order to better understand their meaning for ocean circulation changes and a possible relationship to global climate change on the other hand certain physical and biological processes have the potential to put the reliability of alkenone sst curves into question accordingly examples for possible effects of bioturbational mixing lateral transport of remote alkenones diagnetic alteration and degradation of alkenone composition biogeographic and temporal diversity changes in alkenone producing algae as well as the influence of changes in salinity and nutrient conditions on the alkenone paleotemperature signal are briefly mentioned highlighting the need for more detailed future studies on these issues finally a short summary on the status of the use of the 13calkenones signal as a proxy for past variations in the carbon dioxide pressure pco2 in ocean surface waters and related problems is given

characteristics of alkenones synthesized by a bloom of emiliania huxleyi in the bering sea abstract we investigated the characteristics of the alkenones produced by a bloom of emiliania huxleyi in the eastern bering sea in 2000 alkenones were detected in surface waters between 57 n and 63 n where phosphate concentrations were low and the ammonium nitrate ratio was high the total alkenone content c37 2 c37 3 and c37 4 ranged from 22 0 to 349 g g 1 in suspended particles and from 0 109 to 1 42 g g 1 in surface sediments this suggests that a large proportion of the particulate alkenones synthesized in the surface water rapidly degraded within the water column and or at the water sediment interface of the bering shelf the change in the stable carbon isotopic composition 13c of c37 3 alkenone could not be explained only by variation in co2 aq in the surface water but also depended on the growth rate of e huxleyi the alkenone unsaturation index uk 37 was converted into an alkenone temperature with three equations prahl et al 1988 sikes et al 1997 muller et al 1998 sikes et al s 1997 equation gave the best correlation with the observed sea surface temperature sst in the eastern bering sea however some temperatures estimated by sikes et al s 1997 equation from the uk 37 varied from the observed sst possibly because of the rapidly changing rate of alkenone synthesis in the logarithmic growth stage or the low rate of alkenone synthesis when nutrients were limiting temperatures estimated from uk 37 in the surface sediments 6 8 8 2 c matched the observed sst in september 7 8 c but differed from the annual average sst of 4 to 5 c suggesting that most of the alkenone in the eastern bering sea was synthesized during limited periods for instance in september the relative amounts of c37 4 alkenone as proportions of the total alkenones referred to as c37 4 were high ranging from 18 3 to 41 4 low salinity water

reconstruction of paleoproductivity in the sea of okhotsk over the last 30 kyr 1 marine and terrestrial derived biomarkers alkenones brassicasterol dinosterol and long chain n alkanes as well as carbonate biogenic opal and ice rafted debris ird were measured in two sediment cores in the sea of okhotsk which is located in the northwestern pacific rim and characterized by high primary productivity down core profiles of phytoplankton markers suggest that primary productivity abruptly increased during the global meltwater pulse events 1a about 14 ka and 1b about 11 ka and stayed high in the holocene spatial and temporal distributions of the phytoplankton productivity were found to be consistent with changes in the reconstructed sea ice distribution on the basis of the ird this demonstrates that the progress and retreat of sea ice regulated primary productivity in the sea of okhotsk with minimum productivity during the glacial period the mass accumulation rates of alkenones caco3 and biogenic opal indicate that the dominant phytoplankton species during deglaciation was the coccolithophorid emiliania huxleyi which was replaced by diatoms in the late holocene such a phytoplankton succession was probably caused by an increase in silicate supply to the euphotic layer possibly associated with a change in surface hydrography and or linked to enhanced upwelling of north pacific deep water index terms 1050 geochemistry marine geochemistry 4835 4850 1055 geochemistry organic geochemistry 4267 oceanography general paleoceanography keywords okhotsk sea paleoproductivity sediment citation seki o m ikehara k kawamura t nakatsuka k ohnishi m wakatsuchi h narita and t sakamoto 2004 reconstruction of paleoproductivity in the sea of okhotsk over the last 30 kyr paleoceanography 19 pa1016

the organic geochemistry of peru margin surface sediments i a comparison of the c37 alkenone and historical el nino records abstract the alkenone u k 37 paleothermometer has potential as a sedimentary marker for el nino southern oscillation enso events in the peru upwelling regime we assessed this potential by comparing the historical enso record with detailed u k 37 profiles for 210 pb dated cores from the peru margin oxygen minimum zone omz sediments with the greatest potential for holding a sedimentary u k 37 record of el nino events are sediments from the center of the omz sectioned at intervals the yearly sedimentation rate the u k 37 signals of individual el nino events were substantially attenuated in the sediments we examined and periods of frequent enso activity e g 1870 1891 were more readily identified than isolated enso events in periods of less frequent enso activity detailed depth profiles of the c 37 alkenones in a core from 253 m o 2 k 37 values for the five 2 mm sections from 0 1 cm suggests that the u k 37 may be unaffected by the alkenone loss correlation between the c 37 alkenone concentration profiles in two cores from 15 s collected nine years apart are consistent with the use of these compounds for molecular stratigraphy

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

environmental controls on long chain alkenone occurrence and compositional patterns in lacustrine sediments northwestern china abstract long chain alkenones occur widely in lacustrine settings and their compositions are potential proxies for reconstructing terrestrial paleoclimatological and paleoenvironmental changes however factors influencing their occurrence abundance compositional pattern and unsaturation indices are not well understood here we investigated the alkenones in surface sediments from 19 lakes in northwestern china as well as potential environmental factors of the lakes 12 contain long chain alkenones 3 have the isomeric c 37 3 alkenone and 3 have very low abundance of alkenones our results show that salinity has a substantial influence on the occurrence concentration and compositional pattern most of the compositions are dominated by tri unsaturated compounds with c 38 methyl ketones absent the predominance of c 37 4 and the occurrence of a c 37 3 isomer are suggested to be responses to low salinity as both are only found in the three alkenone containing freshwater lakes the proportion of c 37 4 varies by up to 50 and shows a negative relationship with salinity within the surveyed region an arched relationship of alkenone content and salinity is apparent with no or very low contents of alkenones in freshwater salinity 100 g l environments the u 37 k index is suggested to be a better terrestrial temperature proxy than u 37 k as u 37 k values from lakes containing elevated alkenone content are all within the ranges of published u 37 k temperature calibrations and u 37 k values show a weak positive relationship with salinity

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

a detailed comparison of the uk 37 and coccolith records over the past 290 kyears implications to the alkenone paleotemperature method the uk 37 record and the coccolithophorid remains in a sediment core from the north atlantic ocean have been compared to assess the possible influence of changes in alkenone producing coccolithophorids on the uk 37 sea surface temperature relationship we have determined three major reversals in the populations of noelaerhabdaceae gephyrocapsa and emiliania species in the central north atlantic over the last 290 kyears 245 260 170 and 40 50 kyears bp a detailed comparison of the uk 37 and coccolithophorid records revealed the absence of significant changes in the uk 37 values despite major changes in coccolithophorid assemblages the data indicate that changes in alkenone producing organisms in the past do not involve significant changes in the uk 37 temperature relationship and that the succession did not primarily depend on climatic change it also supports the fact that the uk 37 derived sst differences observed between glacial stages 2 4 6 and 8 are not related to the succession of coccolithophorid species

brief interstadial events in the santa barbara basin ne pacific during the past 60 kyr the instability of the northern hemisphere glacial climate over the past 100 kyr has been revealed by at least 20 brief warm interstadial episodes called dansgaard oeschger events recorded in greenland ice cores1 3 and in north atlantic sedimentary records4 5 a few of these events have been recognized elsewhere6 8 here we describe a record of ocean oxygenation and circulation from the santa barbara basin in the northeast pacific ocean which correlates well with the greenland ice core records we see 19 of the 20 dansgaard oeschger events in the form of laminated sediments deposited under anoxic conditions and we can correlate at least 16 of these with the 17 ice core interstadials of the past 60 kyr thus these short term events were not restricted to the north atlantic region the events had substantial ecological and oceanographic effects in the santa barbara basin including changes in benthic faunal populations and in the age and composition of bottom waters similar ventilation changes have been seen in the gulf of california9 10 suggesting that these changes may have been widespread and synchronous along the northeast pacific margin these results suggest sensitivity of broad areas of the ocean atmosphere cryosphere system to short term climate change

early diagenesis of lipid biomarker compounds in north atlantic sediments near surface sediments 0 45 mm depth interval from the iceland basin 59 n 21 w 3070 m water depth and biscay abyssal plain 48 n 17 w 4105 m water depth were sectioned at millimeter scale resolution to assess alterations in key lipid biomarkers during early diagenesis inventories g cm 2 in the topmost 45 mm of biomarkers from presumed terrestrial sources c20 linear n alkanes n alkanoic acids n alkanols and from phytoplankton sources phytosterols long chain alkenones and alkenoates were 1 5 4 times more abundant in the iceland basin core than in the biscay abyssal plain core indicating greater sedimentary inputs and or preservation at the iceland basin site biomarker concentrations varied significantly over millimeter scale depth intervals pronounced subsurface concentration maxima were present at both sites at the biscay abyssal plain site steep concentration gradients in the uppermost few mm of the sediment column indicate extensive diagenetic losses at or near the sediment water interface strong covariance was seen in the concentrations of various compounds within each class e g long chain n alkanes n alkanols n alkanoic acids and long chain alkenones and alkyl alkenoates indicating that individual compounds within each class are associated with the same organic matrix and have similar degradation and mixing rates thus biomarker indices for assessment of land derived inputs cpi c29 c31 acl and sea surface temperature ipt remain largely unaltered by early diagenetic processes in oxic abyssal sediments in spite of extensive bioturbation and degradative losses within the uppermost few centimeters of the sediment column

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

comparison of mg ca and alkenone based sea surface temperature estimates in the fresh water influenced gulf of guinea eastern equatorial atlantic this study presents a comparison of sea surface temperature sst estimates based on mg ca ratios of globigerinoides ruber and alkenone unsaturation index u37 k in core sediment recovered from the gulf of guinea eastern equatorial atlantic mg ca and u37 k based sst estimates yield fairly comparable results for the time interval 21 000 14 500 years and for the late holocene the early and middle holocene however are largely characterized by a discrepant trend with warm mg ca and cold u37 k based sst estimates this discrepant sst trend is accompanied by low sea surface salinity estimates high riverine runoff and biogenic sediment which is characterized by high biogenic opal content low carbonate content and relatively low alkenone concentration we hypothesize that the discrepancy in the reconstructed ssts during the middle and early holocene presumably suggests a period of elevated riverine input of dissolved silica and dominantly siliceous phytoplankton bloom in a low saline and warm surface water while alkenone producers were likely prevalent in a season of cold sst and low riverine silica input this study suggests that changes in the local hydrography and nutrient input have strong influence on the u37 k based sst estimate that may be unraveled by combining different sst proxies

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

the alkenone temperature signal in western north atlantic surface waters abstract haptophyte algae derived long chain c 37 c 39 alkenones and alkyl alkenoates were analyzed in euphotic zone particulate matter collected over a 7 yr period at the oceanic flux program bermuda atlantic time series ofp bats site in the western sargasso sea surface water temperatures at the site range annually from 19 to 29 c alkenone concentrations ranged from 1 in summer to 100 ng l 1 following the passage of storms highest seasonal concentrations occurred during the late winter and spring under stratified conditions alkenone concentrations in the surface mixed layer 0 20 m were generally 2 to 4 times higher than in the deep fluorescent maximum 75 110 m consistent with emiliania huxleyi concentration profiles haidar and thierstein 2001 and indicated that alkenone production primarily occurs within the upper euphotic zone in this region alkenone compound distributions and the temperature calibrations of c 37 and c 38 methyl and ethyl alkenone unsaturation u 37 k u 38me k and u 38et k respectively were remarkably similar to that observed in an e huxleyi strain previously isolated from the same area conte et al 1998 providing strong evidence that e huxleyi is the predominant alkenone synthesizer and that characteristics exhibited by randomly isolated clones in culture are in many cases consistent with those of populations in the region of origin the bermuda calibration of u 37 k vs water temperature u 37 k 1 9835 0 2004t 0 0034t 2 r 2 0 95 n 91 is nonlinear and falls along the same trendline as euphotic zone particulates from warm 15 c waters of the eastern north atlantic conte and eglinton 1993 and mediterranean ternois et al 1997 the combined north atlantic temperature calibration u 37 k 1 1365 0 1257t 0 0018t 2 r 2 0 963 n 134 differs significantly from published coretop sediment calibrations rosell mele et al 1995 muller et al 1998 based on sea surface temperature maps levitus and boyer 1994 having a steeper slope at temperatures 24 c the reasons are not clearly apparent and manifest a need for detailed studies linking production patterns in surface waters with the signal arriving at the seafloor to fully understand the generation of the sedimentary signal

alkenone sea surface temperatures in the japan sea over the past 36 kyr warm temperatures at the last glacial maximum the japan sea experienced bottom water anoxia at the last glacial maximum lgm since it is surrounded by four shallow straits the sill depths of which are close to or shallower than the drop in sea level 120 m that occurred then a distinctive negative d 18 o excursion of planktonic foraminifera also took place during the lgm this excursion has been interpreted from foraminiferal data as recording a drop in the paleosalinity of surface waters on the assumption of a constant low sea surface temperatures between 34 and 11 ka we present here a profile of alkenonebased sea surface temperatures alkenone ssts over the past 36 kyr our results suggest that ssts during the lgm were much higher than those previously assumed after considering the factors that might aaect estimation of alkenone ssts and comparisons of core top alkenone ssts values with values for modern seawater we conclude that the higher alkenone ssts during the lgm are reliable and reasonable these warm ssts were probably caused by radiative equilibrium associated with the development of stable water stratification in the japan sea during the lgm 2001 elsevier science ltd all rights reserved

alkenone producers during late oligocene early miocene revisited this study investigates ancient alkenone producers among the late oligocene early miocene coccolithophores recorded at deep sea drilling project dsdp site 516 contrary to common assumptions reticulofenestra was not the most important alkenone producer throughout the studied time interval the comparison between coccolith species specific absolute abundances and alkenone contents in the same sedimentary samples shows that cyclicargolithus abundances explain 40 of the total variance of alkenone concentration and that the species cyclicargolithus floridanus was a major alkenone producer although other related taxa may have also contributed to the alkenone production at dsdp site 516 the distribution of the different alkenone isomers mec37 2 etc38 2 and mec38 2 remained unchanged across distinct changes in species composition suggesting similar diunsaturated alkenone compositions within the noelaerhabdaceae family during the late oligocene early miocene however the overall larger cell size of cyclicargolithus may have implications for the alkenone based reconstruction of past partial pressure of co2 our results underscore the importance of a careful evaluation of the most likely alkenone producers for periods 1 85 ma predating the first occurrence of contemporary alkenone producers i e emiliania huxleyi and gephyrocapsa oceanica

long chain unsaturated ketones and esters in living algae and marine sediments abstract series of c37 c39 di and triunsaturated ketones and methyl and ethyl esters of hexatriacontadienoic acid c36 2 have been previously identified in marine sediments and the coccolithophorid emiliania huxleyi these compounds have now been found in four further species of the isochrysidales prymnesiophyta which are not known to bear coccoliths suggesting that they are more widely distributed in living algae than previously thought in addition the ketones have been recognised in sediments of eocene age ca 45 ma which greatly extends their known geological time range and increases their potential as molecular markers for algal input heptatriacontatetraen 2 one c37 4 octatriacontatetraen 3 one c38 4 methyl and ethyl esters of hexatriacontatrienoic acid c36 3 and the ethyl ester of hexatriacontatetraenoic acid c36 4 have also been identified in varying amounts in these algae by gas chromatography and computerised gas chromatography mass spectrometry

organic geochemical evidence of late pleistocene holocene environmental changes in the lake balaton region hungary abstract this paper presents organic geochemical records and a combined interpretation of organic geochemical and palaeoecological data for a late pleistocene holocene shallow lake sequence abundance bulk chemical composition and sources of the organic matter om as well as the relative contribution of the labile and resistant bio and geo macromolecules were determined on 46 sediment samples lipids isolated from selected samples representing the lowest and highest water levels were analyzed integration of the organic geochemical and palaeoecological records suggests that climate exerted the primary control on the amount and quality of the om preserved the relative contribution of the labile fresh plant and litter and resistant lignin and cellulose bio macromolecules immature geo macromolecules humic substances and mature refractory geo macromolecules and the degree of preservation of the primary biomass calculated from mathematical deconvolution of rock eval pyrograms allowed the distinction of three and five zones related mainly to water level fluctuation within the late pleistocene and holocene sequences respectively

decoding sea surface and paleoclimate conditions in the eastern mediterranean over the tortonian messinian transition abstract new sedimentological micropaleontological and geochemical data from the upper miocene pre evaporitic sedimentary sequence of the faneromeni section crete island eastern mediterranean revealed a stepwise restriction of the mediterranean sea preceding the messinian salinity crisis msc which was modulated by a sedimentary cyclicity responding to orbital parameters this cyclicity is manifested by lithological alternations from laminated to indurated homogeneous marls and clayey limestones and covers the tortonian messinian transition tmt 7 6 6 7 ma this time window covers the successive closure of the marine mediterranean atlantic gateways which culminated in the onset of the msc in the present study we present the first evidence for changes in the upper water column reflected by sea surface temperature sst and salinity sss variations that correlate with pronounced paleoclimatic fluctuations planktonic foraminiferal isotopes in combination with paired mixed layer sr ca derived sst data reveal that the very warm late tortonian interval has been followed by a strong long term cooling 10 c and desalination 10 trend during the earliest messinian attributed to the paroxysmal phase of the so called siphon event in particular the climate shift that occurred at the end of a global carbon isotope 13c decrease suggests that changes in the carbon cycle were instrumental in driving late miocene climate dynamics cooling and aridity in the progressively isolated eastern mediterranean sea the observed salinity variability during this time interval also provides further insights about seasonal freshwater inputs and gives new support to the much debated hydrologic regime linear salinity increase vs step function evolution with strong salinity fluctuations preceding the deposition of evaporites the novel methodology of foraminiferal sr ca paleothermometry and results of this study could have numerous potential applications to other regions and relevant extreme geological events therefore in the near future we expect this approach to add important new information to our understanding of neogene climates

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

non annual laminations and expansion of anoxic basin floor conditions in santa monica basin california borderland over the past four centuries sediments from box cores in the deep portion of santa monica basin have been examined by x radiography and the upper 10 20 cm are characterized by laminations 1 5 mm in thickness age dating of 9 cores by 210pb analysis has shown that accumulation rates on the central basin floor have been remarkably constant during the past century averaging 16 0 0 4 mg cm2 yr densitometer analysis of the x radiography films from 7 cores and spectral analysis of the resulting time series indicates that most lamination couplets have a periodicity in the 3 7 year range a range matching that of the el nino southern oscillation periodicity the median periodicity appears to have decreased slightly during the past 3 centuries from 7 0 years during 200 300 yrs b p to 5 2 yrs during 0 100 yrs b p this trend could be due to a decreasing sedimentation rate an increasing forcing frequency or an increasingly faithful response of the basin in more recent years multiple processes have contributed to creation of the laminations in santa monica basin the principal factors appear to be 1 variations in porosity due to the relative abundance of organic filaments probably formed by beggiatoa mats and 2 compositional variations that reflect variations in carbonate lithogenous ratios and in grain size both of these are expected to respond to enso events the presence of near anoxic bottom waters has prevented bioturbation permitting laminations to be preserved basin bottom waters became nearly anoxic about 350 years ago at the onset of warming as the little ice age waned expansion of the near anoxic area during the past century may have been augmented by 20th century anthropogenic effects the style of these non annual laminations in santa monica basin matches that of the annual laminations in the adjacent santa barbara basin and demonstrates the need for caution in interpreting all laminations as representing annual varves

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

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

depositional events in santa monica basin california borderland over the past five centuries the southern california coastal climate is characterized by decadal and generational floods that discharge one to three orders of magnitude more sediment than the average annual contribution these can produce turbidity currents directly or load the canyons and slopes with sediments that then may fail and form turbidity flows seismic activity is high on this transform margin and can trigger slope failures where slope sedimentation rates are high and sediments are unstable these events produce slope failures and slides and slumps in canyon heads which evolve into turbidity currents of sufficient volume to reach the adjacent margin basin floors such events occur at approximately century frequency this paper describes six basin floor turbidites that have been mapped in box cores sampling roughly the top 40 50 cm from the basin floor or santa monica basin in the california borderland these deposits were laid down during the past 500 years of record their depositional areas have been conservatively estimated to range from 500 to almost 1500 km2 and contain masses of sediment ranging from 10 000 000 to 100 000 000 tons this compares with a long term average annual terrigenous contribution rate of about 4 000 000 tons yr from the adjacent major streams although annual rates vary from 0 to 60 000 000 tons over the last century of record three of the six events have been related to two major floods 1884 6 1969 and to one major seismic event the mission earthquakes of 1822 1812 the older turbidites were deposited before european entry to the area and cannot be assigned to an historic event but from their size were probably seismically triggered and are the largest of the six events it is likely that other smaller events are masked by the more recent turbidites particularly in the area where box cores are dominantly composed of turbidites these features exhibit average outcrop thickness of 2 to 7 cm with maxima of the order of 10 cm thickness yet represent major events and significant volumes of sediment they also document that the two major sources for such events floods and seismic events produce deposits of very different mass and can probably be separated in the record on that basis thus the frequency of major floods and of major earthquakes in the region could be defined from study of such deposits in longer cores these deposits also provide examples of continued turbidity current activity to the basin floors at a time of high sea level this is contrary to the passive models for sequence stratigraphy depositional patterns

lipid distributions in loess paleosol sequences from northwest china molecular stratigraphic analyses using gc ms have been performed on the top section of the jiuzhoutai loess paleosol sequences near lanzhou in northwest china with a record extending from the second last interglacial through the present interglacial the various molecular fossils identified from the second order loess and paleosol layers include c14 c35n alkanes c8 c30n alkanoic acids c12 c30n alkanols and c23 c33n alkan 2 ones the cpi carbon preference index values and the ratio of c29 c31n alkan 2 ones display alternations between loess deposits and paleosols they show a significant correlation with the loess magnetic susceptibility an indicator of the east asian summer monsoon the observed variations of the ketone indices in relation to the change of lithology are proposed to result from microbial re working of higher plant inputs in the paleosols

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

depth and seasonality of alkenone production along the california margin inferred from a core top transect alkenone unsaturation indices uk 37 of marine sediment could prove particularly useful on organic rich continental margins where carbonate dissolution hampers the use of other paleoclimatic proxies mccaffrey et al 1990 kennedy and brassell 1992 forty core top samples of recent sediment from a latitudinal transect 23 40 n along the california margin yield uk 37 values that correlate linearly with modern mean annual sea surface temperatures ssts in the range of 12 23 c reproducibility of the unsaturation value in closely spaced cores is near analytical error uk 37 data define a relationship to temperature nearly identical to the prahl et al 1988 laboratory cultures of emiliania huxleyi the close agreement is particularly significant in light of the nannofossil composition of the sediments where the abundance of the coccolith taxon gephyrocapsa oceanica known to synthesize alkenones equals or exceeds that of e huxleyi comparison with seasonal temperature variations at different depths indicates that little if any alkenone production occurs at depths 30 m along the continental margin water depths 2 km sediments in more pelagic locations exhibit small but consistent biases toward winter and or subsurface production similar to previously reported sediment trap and core top data from the oregon margin prahl et al 1993 doose et al 1997

core top calibration of the lipid based u37k and tex86 temperature proxies on the southern italian shelf sw adriatic sea gulf of taranto abstract the mediterranean sea is at the transition between temperate and tropical air masses and as such of importance for studying climate change the gulf of taranto and adjacent sw adriatic sea are at the heart of this region their sediments are excellently suited for generating high quality environmental records for the last millennia with a sub decadal resolution the quality of these records is dependent on a careful calibration of the transfer functions used to translate the sedimentary lipid signals to the local environment here we examine and calibrate the u 37 k and tex 86 lipid based temperature proxies in 48 surface sediments and relate these to ambient sea surface temperatures and other environmental data the u 37 k based temperatures in surface sediments reflect winter spring sea surface temperatures in agreement with other studies demonstrating maximum haptophyte production during the colder season the tex 86 based temperatures for the nearshore sites also reflect winter sea surface temperatures however at the most offshore sites they correspond to summer sea surface temperatures additional lipid and environmental data including the distribution of the bit index and remote sensed chlorophyll a suggest a shoreward increase of the impact of seasonal and spatial variability in nutrients and control of planktonic archaeal abundance by primary productivity particle loading in surface waters and or overprint by a cold biased terrestrial tex 86 signal as such the offshore tex 86 values seem to reflect a true summer signal to the effect that offshore u 37 k and tex 86 reconstruct winter and summer temperature respectively and hence provide information on the annual temperature amplitude

eastern mediterranean surface water temperatures and d18o composition during deposition of sapropels in the late quaternary 0indices and d 18 o of planktonic foraminifer calcite d 18 ofc across late pleistocene sapropel intervals show that d 18 ofc decreased between 1 and 4 6 and sst increased between 0 7 and 6 7 c maximal d 18 oseawater depletion of eastern mediterranean surface waters at the transition is between 0 5 and 3 0 and in all but one case exceeded the depletion seen in a western mediterranean core the depletion in d 18 oseawater is most pronounced at sapropel bases in agreement with an initial sudden input of monsoon derived freshwater most sapropels coincide with warming trends of sst the density decrease by initial freshwater input and continued warming of the sea surface pooled fresh water in the surface layer and prohibited deep convection down to ageing deep water emplaced during cold and arid glacial conditions an exception to this pattern is glacial sapropel s6 its largest d 18 oseawater depletion 3 is almost matched by the depletion in the western mediterranean sea and it is accompanied by surface water cooling following an initially rapid warming phase a second period of significant isotopic depletion is in isotope stage 6 at the 150 kyr insolation maximum while not expressed as a sapropel due to cold sst it is in accord with a strengthened monsoon in the southern catchment index terms 1055 geochemistry organic geochemistry 1620 global change climate dynamics 3309 4267 oceanography general paleoceanography 9604 information related to geologic time cenozoic keywords mediterranean sea sapropels sea surface temperatures oxygen isotopes quaternary citation emeis k c et al eastern mediterranean surface water temperatures and d 18 o composition during deposition of sapropels

geochemical test for branching decay of 176lu abstract two different groups of values for the 176lu decay constant have been determined by recent high precision experiments the 176lu values of 1 86 1 87 10 11 a 1 were determined by age comparisons using terrestrial minerals of proterozoic and late archean age whereas values of 1 94 10 11 a 1 were determined in age comparison studies of meteorites a possible branched decay of 176lu could be the cause of this discrepancy the decay of 176lu to 176yb was detected in the early studies of radioactivity of 176lu with reported values of in the total 176lu ranging from less than 0 03 to 0 67 if the decay fraction is close to the upper limit of the reported values it can explain the 4 6 difference between the apparent 176lu values to get a reliable estimate for the decay of 176lu we have measured yb isotopic composition in 2 7 ga zircons with lu ybn chondrite normalized ratios of 1 40 and 1 45 in 1 0 ga xenotime with lu ybn 1 23 using yb from the 28 4 ma fish canyon tuff fct zircon and titanite as the modern reference value multiple analyses yielded the following weighted mean values 2 for the 176yb 174yb ratio 0 4022134 0 0000017 for the fct zircon and titanite 0 4022134 0 0000019 for the 1 0 ga xenotime and 0 4022124 0 0000033 for the 2 7 ga zircons these data yield 0 005 0 015 2 and establish an upper limit of 0 9 of total decays for the decay branch branching decay can therefore be eliminated as the cause of the discrepancy in 176lu decay constant estimates we discuss other possible causes of the 176lu terrestrial vs meteorite discrepancy

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

proceedings of a workshop on alkenone based paleoceanographic indicators 1 the papers in this theme derive from a workshop on alkenone based paleoceanographic indicators held at the j erik jonsson center of the national academy of sciences in woods hole massachusetts october 3 6 1999 the papers fall into two groups position papers prepared in advance of the workshop by the leaders of six different working groups and reports prepared during and after the workshop by rapporteurs and members of the working groups their publication here is intended to provide a record of the discussions and thus to serve to the paleoceanographic community an overview of the conference and its participants is also provided

reconciling discrepancies between uk37 and mg ca reconstructions of holocene marine temperature variability significant discrepancies exist between the detrended variability of late holocene marine temperatures inferred from mg ca and uk37 proxies with the former showing substantially more centennial scale variation than the latter discrepancies exceed that attributable to differences in location and persist across various calibrations indicating that they are intrinsic to the proxy measurement we demonstrate that these discrepancies can be reconciled using a statistical model that accounts for the effects of bioturbation sampling and measurement noise and aliasing of seasonal variability the smaller number of individual samples incorporated into mg ca measurements relative to uk37 measurements leads to greater aliasing and generally accounts for the differences in the magnitude and distribution of variability an inverse application of the statistical model is also developed and applied in order to estimate the spectrum of marine temperature variability after correcting for proxy distortions the correction method is tested on surrogate data and shown to reliably estimate the spectrum of temperature variance when using high resolution records applying this inverse method to the actual mg ca and uk37 data results in estimates of the spectrum of temperature variance that are consistent this approach provides a basis by which to accurately estimate the distribution of intrinsic marine temperature variability from marine proxy records

alkenones as paleoceanographic proxies 1 alkenone derived estimates of temperature and co2 are contributing to our understanding of earth s climate history in order to increase confidence in alkenone based climate proxies we recommend the following actions first the sedimentary component or fraction containing alkenones should be identified in order to assess the impact of horizontal advection and vertical mixing on alkenone derived temperature and co2 estimates second differential mixing rates of alkenone containing particles and sand sized foraminifera should be quantified by independent dating of the two phases until that is accomplished apparent temporal offsets of climate proxies in the two phases should be interpreted cautiously third the stability of the unsaturation ratio and carbon isotopic compositions of alkenones during all phases of diagenesis should be confirmed both field and laboratory observations are required fourth future alkenone investigations should be coupled with other paleoclimate proxy measurements at high deposition rate sites in a variety of oceanographic settings in upwelling regions and in the vicinity of river plumes salinity and nutrient proxies should be measured since changes in these parameters may affect alkenone biosynthesis

timescales of lateral sediment transport in the panama basin as revealed by radiocarbon ages of alkenones total organic carbon and foraminifera abstract paired radiocarbon measurements on haptophyte biomarkers alkenones and on co occurring tests of planktic foraminifera neogloboquadrina dutertrei and globogerinoides sacculifer from late glacial to holocene sediments at core locations me0005 24jc y69 71p and mc16 from the south western and central panama basin indicate no significant addition of pre aged alkenones by lateral advection the strong temporal correspondence between alkenones foraminifera and total organic carbon toc also implies negligible contributions of aged terrigenous material considering controversial evidence for sediment redistribution in previous studies of these sites our data imply that the laterally supplied material cannot stem from remobilization of substantially aged sediments transport if any requires syn depositional nepheloid layer transport and redistribution of low density or fine grained components within decades of particle formation such rapid and local transport minimizes the potential for temporal decoupling of proxies residing in different grain size fractions and thus facilitates comparison of various proxies for paleoceanographic reconstructions in this study area anomalously old foraminiferal tests from a glacial depth interval of core y69 71p may result from episodic spillover of fast bottom currents across the carnegie ridge transporting foraminiferal sands towards the north

palaeoclimatic signals recognized by chemometric treatment of molecular stratigraphic data abstract the high resolution stratigraphy of various marker compounds has been studied using gc hplc and gc ms in a 13 m gravity core recovered from the kane gap region eastern equatorial atlantic which provides a record of the glacial interglacial episodes over the last million years downhole variations in many presumed source specific components are observed e g in n alkanes from terrigenous land plants and dinosterol from dinoflagellates which may be due to perturbations or cyclicities resulting from climatic change fluctuations in the unsaturation of alkenones attributable to variations in water temperatures show correlations with the glacial interglacial cycles recorded in the 18 o values for planktonic foraminifera thereby providing a potential organic geochemical measure of past climates these molecular abundance data can be linked to the palaeotemperature record following computer treatments using principal component and spectral analyses molecular stratigraphy shows promise as a new chemostratigraphical tool where other means of stratigraphy fail for example through calcium carbonate dissolution

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

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

variability in two deep coastal basins santa monica and san pedro off southern california time series of midbasin hydrographic samples and of an array of moored temperature velocity sensors are used to examine subtidal to interannual scale variability in two 900 m deep basins off the southern california coast the deepest sill that allows entry into the basins is at 740 m and the two basins santa monica and san pedro are separated by a sill about 40 m high the mean flow 40 m above and 60 m below the 740 m sill depth is in the counterclockwise direction and the magnitude is 0 5 1 0 cm s 1 the data indicate that the waters at deeper levels of the basins are neither quiescent at one extreme nor are they filled with random noise at the other extreme rather at all scales examined the variability is significant and much of it is spatially coherent the amplitude of the subtidal velocity fluctuations is 4 cm s 1 almost an order of magnitude greater than that of the mean flow the amplitude of the subtidal temperature fluctuations is 0 1 c at 700 m and 0 05 c at 800 m the temperature variance is roughly a factor of 2 smaller at midbasin than on the basin perimeter this is not the case with the velocity variance which is generally greatest at midbasin and on the coastal edges of both basins much of the subtidal variability in both temperature and velocity appears to be associated with topographic waves that travel counterclockwise around the pair of basins the observed period of the waves 10 20 days is roughly consistent with that predicted by a barotropic model of free waves in an elliptical basin mysak 1985 comparison of time series of currents in the upper 200 m water column with those in the lower water column suggests that the waves are forced by the circulation in the upper water column which is directed over rather than around the basins seasonal variability was observed in both temperature and velocity fields as deep as 800 m i e below the depth of the deepest sill along the perimeters of both basins and at midbasin in santa monica but not in san pedro temperature increases and salinity and density decrease from spring to fall consistent with the seasonal development of the poleward flowing california countercurrent in the upper water column the seasonal cycle of water properties has significant spatial variability over the basins the amplitude is a factor of 2 greater on the seaward side of santa monica basin than at midbasin and on its coastal edges and on the edges of san pedro basin the variance of the subtidal velocity and temperature fields also exhibit a seasonal signal maximum variance occurs during fall minimum variance occurs during spring interannual variability dominates the 4 year time series of water properties of the near bottom water in each basin and differs somewhat between the two basins the interannual variability is dominated by events associated with renewal of basin bottom water two such events were identified a minor one in 1987 and a major one in 1988 each beginning in may of that year in both cases the actual renewal occurs in less than a month and the most rapid return to near normal conditions occurs over a period of about 3 5 months

comparison of organic uk 37 texh86 ldi and faunal proxies foraminiferal assemblages for reconstruction of late quaternary sea surface temperature variability from offshore southeastern australia several proxies have been developed to reconstruct past sea surface temperature sst but different proxies may reflect temperatures of different seasons and each proxy is characterized by certain uncertainties therefore a multiproxy approach is preferred to precisely reconstruct sst here we reconstruct sst of the ocean offshore southeastern australia murray canyons area for the last 135 ka using three independent organic proxies texh86 based on glycerol dialkyl glycerol tetraethers gdgts uk 37 based on alkenones and ldi based on long chain diols in addition to foraminiferal faunal assemblages the organic proxy records show similar trends with the highest temperature 21 c for uk 37 and texh86 and 25 c for ldi during the last interglacial and lowest temperature 8 c for texh86 10 c for uk 37 and 12 c for ldi during the last glacial maximum however the differences in absolute sst estimates obtained by the organic proxies varied over time with differences of up to 9 c between ldi and texh86 the seasonal sst reconstructions based on the modern analogue of foraminiferal assemblages also show similar trends as the organic proxies with highest temperatures during the last interglacial 23 c for the warmest month sst 20 c for mean annual and 18 c for the coolest month and lowest temperature during the last glacial maximum 14 c for the warmest month 11 c for mean annual and 9 c for the coolest month down core comparison between the reconstructed ssts of the organic and inorganic proxies shows that ldi inferred temperatures compare well with the temperature of the warmest month texh86 with the temperature of the coolest month and uk 37 with mean annual temperature an increase in texh86 sst estimates relative to those of other proxies during deglaciations and interglacials suggests that either winter temperatures rapidly warmed possibly due to an invigoration of the leeuwin current over the core site or there was a change in the growth season of the thaumarchaeota the source organism of gdgts our study shows the benefits of a multiproxy approach in the interpretation of sst proxies leading to a more robust knowledge of past ocean temperature changes

lipid distribution in a subtropical southern china stalagmite as a record of soil ecosystem response to paleoclimate change abstract lipid extracts from a 61 7 cm long subtropical stalagmite in southern china spanning the period of ca 10 000 21 000 yr ago as constrained by u th dating were analyzed using gas chromatography mass spectrometry the higher plants and microorganisms in the overlying soils contribute a proportion of n alkanes identified in the stalagmite the occurrence of lmw lower molecular weight n alkanols and n alkan 2 ones in the stalagmite was mainly related to the soil microorganisms we suggest that hmw higher molecular weight n alkanols and n alkan 2 ones identified in the stalagmite originate from soil organics and reflect input from contemporary vegetation shifts in the ratio of lmw to hmw n alkanols or n alkan 2 ones indicative of the variation of soil ecosystems e g microbial degradation of organic matter and or the relative abundance of soil microorganisms to higher plants are comparable with the subtropical alkenone sst sea surface temperature record of the same period the similar trends seen in the 13c data and the lipid parameters in this stalagmite imply that the overlying soil ecosystem response to climate might be responsible for the variation of 13c values

radionuclide concentrations fluxes and residence times at santa monica and san pedro basins our participation in the california basin study cabs in 1986 1988 has produced a radionuclide data base that allows us to trace the particle and water movement in the santa monica and the san pedro basins these data enable us to calculate the radionuclide inventories in the three compartments of the basin the water column the settling particles and the sediments we have also determined the fluxes of several radionuclides associated with the sinking particles the residence time in the water column and the rate of deposition in the sediments the biogeochemical environment of the santa monica basin is uniquely suited to the application of tracer techniques to study the sedimentation processes subtle but measurable changes in the distribution of fallout of 137cs from 1977 to 1988 were noted in the water column compared to the decay corrected measurement in 1973 1977 at the geosecs and farallon islands stations off the coast of california 137cs inventory in the water column in santa monica basin has not changed significantly for the past decade increases in the deep water concentration profiles of 137cs particle transport and diagenetic release of cesium in the deep water the major 137cs inventory 70 resides in the upper 400m of water with a mean residence time of 480 90 years less than 11 of the total 137cs inventory was found in the sediments at water depths of 900m in 1987 unlike 137cs more than 80 of the fallout 239 240pu has been deposited in the santa monica basin sediments a mean residence time of 13 2 years was measured for 239 240pu in the basin water the ubiquitous 239 240pu subsurface concentration maximum observed in the pacific oceanic waters at about 350m depth is also evident in the basin water we have no definitive explanation for the persistence of the subsurface maximum except that it appears to be correlated with the density gradient at 26 5 to 26 9 sigma t the 239 240pu flux for settling particles correlates remarkably well with mass flux and it increases with depth in the water column plutonium deposition in anoxic sediments also appears to be useful as a time marker for age dating of sediments and estimating the sediment accumulation rates the sedimentation rates determined by plutonium are shown to be comparable to those estimated by excess 210pb in the cores radionuclide fluxes measured from sediment trap particles in 1986 1988 were lower by a factor of 0 6 0 2 compared to the average fluxes determined from the box core samples radionuclides such as 210pb 137cs and 239 240pu have been shown to be useful tools in the study of biogeochemical processes in the santa monica basin

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

the impact of oxic degradation on long chain alkyl diol distributions in arabian sea surface sediments oxygen exposure has a large impact on lipid biomarker preservation in surface sediments and may affect the application of organic proxies used for reconstructing past environmental conditions to determine its effect on long chain alkyl diol and keto ol based proxies the distributions of these lipids was studied in nine surface sediments from the murray ridge in the arabian sea obtained from varying water depths 900 3000 m but in close lateral proximity and therefore likely receiving a similar particle flux due to substantial differences in bottom water oxygen concentration 3 77 mol l and sedimentation rate substantial differences exist in the time the biomarker lipids are exposed to oxygen in the sediment long chain alkyl diol and keto ol concentrations in the surface sediments 0 0 5 cm decreased progressively with increasing oxygen exposure time suggesting increased oxic degradation the 1 15 keto ol diol ratio doxi increased slightly with oxygen exposure time as diols had apparently slightly higher degradation rates than keto ols the ratio of 1 14 vs 1 13 or 1 15 diols used as upwelling proxies did not show substantial changes however the c30 1 15 diol exhibited a slightly higher degradation rate than c28 and c30 1 13 diols and thus the long chain diol index ldi used as sea surface temperature proxy showed a negative correlation with the maximum residence time in the oxic zone of the sediment resulting in ca 2 3 5 c change when translated to temperature the uk 37 index did not show significant changes with increasing oxygen exposure this suggests that oxic degradation may affect temperature reconstructions using the ldi in oxic settings and where oxygen concentrations have varied substantially over time

upwelling intensification as part of the pliocene pleistocene climate transition a deep sea sediment core underlying the benguela upwelling system off southwest africa provides a continuous time series of sea surface temperature sst for the past 4 5 million years our results indicate that temperatures in the region have declined by about 10 c since 3 2 million years ago records of paleoproductivity suggest that this cooling was associated with an increase in wind driven upwelling tied to a shift from relatively stable global warmth during the mid pliocene to the high amplitude glacial interglacial cycles of the late quaternary these observations imply that atlantic ocean surface water circulation was radically different during the mid pliocene

systematic pattern in u37k temperature residuals for surface sediments from high latitude and other oceanographic settings abstract twenty seven multicores collected in late summer 2004 from coastal and inland marine sites throughout se alaska 55 to 61 n were analyzed for c 37 to c 39 alkenones of specific haptophyte origin this biomarker signal detected in core top sediments from 20 of the sites was quantitatively most significant in organic carbon and biogenic silica rich sediments deposited south of icy strait 58 n along the outer coastline of baranof and prince of wales islands u 37 k based water temperature estimates derived using a standard calibration equation u 37 k 0 034t 0 039 were uniform throughout the study area averaging 11 9 1 0 c a value 4 c warmer than mean annual sst masst for the region epoxides indicative of selective alkenone degradation by an aerobic bacterial process were also detected and quantified in all sediments containing alkenones semi quantitative accounting of the impact that compound selective degradation can impose on alkenone unsaturation patterns indicates the standard u 37 k based temperature estimates could be too warm by a variable amount 0 7 2 4 c depending upon the site with an overall average of 1 4 c even after adjustment for this potential diagenetic warming effect estimates still best match summer and not masst in this subarctic region re examination of alkenone signatures preserved in sediment from the north atlantic and on the continental margin located south of 45 s along the chilean coast indicates the apparent summer signal in u 37 k derived sst estimates is not unique to se alaskan sediments but rather a common finding when alkenone thermometry is applied to sediments from high latitude environments examination of model residuals from analysis of surface sediment samples collected at lower latitude settings along the west coast of the americas also identifies other sites where significant biogeographic patterns seem apparent and viable oceanographic explanations can be offered

the impact of alkenone degradation on uk 37 paleothermometry a model derived assessment the u37k proxy for past sea surface temperature sst is based on the unsaturation ratio of c37 alkenones it is considered a diagenetically robust proxy but biases have been invoked because the index can be altered by preferential degradation of the c37 3 alkenone resulting in higher reconstructed sst however alkenone degradation rate constants are poorly constrained making it difficult to evaluate the plausibility of such a bias therefore we quantitatively assessed the effect of 1 different alkenone degradation rate constants 2 differential degradation factors between di and tri unsaturated c37 alkenones 3 and initial u37k values on the u37k paleothermometer for two depositional environments shelf and upper slope by means of a reaction transport model rtm rtm results reveal that preferential degradation of c37 3 can potentially alter the original signal of the u37k paleothermometer but sst biases sst are largely within u37k calibration error sst 1 5 c are associated with marked downcore decreases in alkenone concentration consequently we caution against the interpretation of u37k indices when extensive degradation results in very low alkenone concentrations 5 ng g 1

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

effects of long term oxic degradation on the u37k tex86 and bit organic proxies abstract one of the primary prerequisites for the application of organic proxies is that they should not be substantially affected by diagenesis however studies have shown that oxic degradation of biomarker lipids can affect their relative distribution we tested the diagenetic stability of the u 37 k and tex86 palaeothermometers upon long term oxygen exposure for this purpose we studied the distributions of alkenones and glycerol dialkyl glycerol tetraethers gdgts in different sections of turbidites at the madeira abyssal plain map that experienced different degrees of oxygen exposure sediments were deposited anoxically on the shelf and then transported by turbidity currents to the map which has oxic bottom water this resulted in partial degradation of the turbidite organic matter as a result of long term exposure to oxic bottom water concentrations of gdgts and alkenones were reduced by one to two orders of magnitude in the oxidized parts of the turbidites compared to the unoxidized parts indicating substantial degradation high resolution analysis of the pleistocene f turbidite showed that the u 37 k index of long chain alkenones increased only slightly 0 01 corresponding to u 37 k while for other pliocene miocene turbidites it either remained unchanged or decreased substantially up to 0 06 corresponding to 6 c previous observations showed that the bit index a proxy for the contribution of soil organic matter to total organic carbon was always substantially higher in the oxidized part in all the turbidites as a result of preferential degradation of marine derived gdgts this relative increase in soil derived gdgts affects tex86 as the isoprenoid gdgt distribution on the continent can be quite different from that in the marine environment our results indicate that the organic proxies are affected by long term oxic degradation to different extents this should be taken into account when applying these proxies in palaeoceanographic studies of sediments which have been exposed to prolonged oxic degradation

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

a 5 million year comparison of mg ca and alkenone paleothermometers geochemical sea surface temperature sst proxies such as the magnesium to calcium ratio mg ca in foraminifera and the alkenone unsaturation index uk 37 are becoming widely used in pre pleistocene climate records this study quantitatively compares previously published mg ca and uk 37 data from ocean drilling program odp site 847 in the eastern equatorial pacific to assess the utility of these proxies to reconstruct tropical sst over the last 5 ma foraminiferal mg ca sst calibrations that include a dissolution correction are most appropriate at this location because they provide sst estimates for the youngest sample that are close to modern mean annual sst the long term trends in the two records are remarkably similar and confirm a 3 5 c cooling trend from the early pliocene warm period to the late pleistocene noted in previous work absolute temperature estimates are similar for both proxies when errors in the dissolution correction used to estimate sst from mg ca are taken into account comparing the two sst records at odp site 847 to other records in the region shows that the eastern equatorial pacific was 2 4 c warmer during the early pliocene compared to today

the geological setting of santa monica and san pedro basins california continental borderland the california continental borderland s present configuration dates from about 4 to 5 106 years before present bp and is the most recent of several configuration of the southern california margin that have evolved after the north america plate over rode the east pacific rise about 30 106 years ago the present morphology is a series of two to three northwest southeast trending rows of depressions separated by banks and insular ridges two inner basins santa monica and san pedro have been the site for the california basin study cabs funded by the us department of energy the santa monica and san pedro basins contain post miocene sediment thicknesses of about 2 5 and 1 5 km respectively during the holocene past 10 000 years about 10 12m have accumulated the sediment entered the basin by one or a combination of processes including particle infall mainly as bioaggregates from surface waters from nepheloid plumes surface mid depth and near bottom from turbidity currents mass movements and to a very minor degree direct precipitation in santa monica basin during the last century particle infall nepheloid plume transport have been the most common processes the former process has been dominant in thecentral basin at water depths from 900 945m where characteristic silt clay is found with a typical mean particle diameter of about 0 0006mm standard deviation 2 skewness near zero kurtosis is typically 2 platykurtic these values indicate broad near log normal particle size distributions the calcium carbonate content averages about 10 and organic carbon about 4 surficial sediment bulk densities are 1 1 1 2 and accumulation rates range from 16 30mg cm 2yr1 in this central fine deposit bottom water oxygen contents are at or below 0 1 ml 1 1 so that bioturbation is inhibited thus preserving the primary sedimentary stratification there appear to be annual varves but the laminae couplets are not simple wet dry season pairs their formation is related to longer period climatic events el nino cycle of 3 to 4 years is dominant and is also affected by aperiodic bottom water flushing events the anoxic zone of bottom water has expanded over the past 300 to 350 years from a samll area in the northeastern basin floor ca 120km2 at 300 years bp and now covers most of the basin floor below depths of about 850m 1290km2 this expansion may have been primarily relaed to ocean circulation rate changes following the little ice age but is also likely to have been strongly affected by subsequent major changes in the natural drainages post european colonization the bottom water oxygen contents must also reflect the introduction of oxidizable pollutants coincident with the shift to agricultural mission era and then to urban use late 19th century to present of the adjacent mainland such localized effects are also suggested by the contrasting very large increases in the area of low oxygen bottom water in santa monica basin relative to the minimal changes in the area of anoxia in santa barbara basin over the same period and the lack of such zone in san pedro basin in the san pedro basin the bottom waters have remained dysaerobic so its sediments are bioturbated and preserve little or no evidence of primary stratification dumping of oil drilling muds and cuttings during the couple of decades prior to 1970 has left a surficial deposit ranging from 1 to 15cm in thickness forming a bull s eye isopach pattern as seen in radiographs bottom water oxygen content is usually 0 2ml o21 1 bottom infauna and epifauna are sparse central basin floor sediments water depths 800m of san pedro basin have textural characteristics similar to those of santa monica basin with distal basin floor surficial sediments being deposited primarily by particle infall and nepheloid flow at the present time mean diameters 0 006mm standard deviation 2 skewness 0 and kurtosis 2 platykurtic calcium carbonate content averages 8 10 and organic carbon is about 4 an estimate of the contemporary sedimentation rate was determined for a single box core of 25 29mg cm 2 yr1 from the central basin near the present distributary margin it cannot be considered necessarily to be representative mixing is indicated by the data an important climatic factor is the alternation of multi year wet and dry periods the california basin study was conducted during an extended dry period of low river discharge this undoubtedly will have affected the conclusions of the study related to sediment water interactions and pollutant transport by suspended clays

salinity control on long chain alkenone distributions in lake surface waters and sediments of the northern qinghai tibetan plateau china abstract long chain alkenones in lacustrine settings are potentially excellent biomarkers for the reconstruction of past terrestrial environmental conditions and have been found in many different types of lakes around the globe a wider range of factors influence the occurrence and distribution of alkenones in lake sediments and waters when compared to marine systems lake environmental conditions such as temperature in particular and salinity are among the key factors controlling alkenone distributions in lacustrine settings here we investigated alkenone distribution patterns in lakes of the northern qinghai tibetan plateau china and their possible relationship with environmental conditions by analyzing paired samples of suspended particulate matter in surface waters and surface sediments salinity of investigated lake waters ranges from almost 0 to 100 g l while temperature variation among the lakes is minimal effectively eliminating temperature effects on the alkenone distribution patterns observed here we show that 1 alkenone concentrations vary substantially between the lakes yet controlling mechanisms remain elusive 2 c37 c38 ratios are substantially lower in the lakes of the qaidam basin than in the lake qinghai region probably indicating different alkenone producers in the two regions and 3 large variations in c37 4 the percentage of the c37 4 alkenone determined from both surface waters and sediments are negatively correlated with salinity we suggest that the c37 4 index could be used as a salinity indicator at least on a regional scale with careful considerations of other potentially complicating factors however potential reasons for why salinity could significantly affect c37 4 values need further investigation