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

eocene climate record of a high southern latitude continental shelf seymour island antarctica a high resolution record of eocene paleotemperature variation is preserved within the high southern latitude marine shelf succession of the la meseta formation on seymour island off the ne side of the antarctic peninsula 87 sr 86 sr ratios of bivalve shell carbonate indicate that the la meseta formation spans virtually the entire eocene and suggest the presence of an early middle eocene unconformity paleoclimatic and paleoceanographic inferences are based on the stable oxygen and carbon isotope values of two genera of bivalves collected with a high degree of stratigraphic resolution within the formation and with multiple replicate samples from each horizon 18 o data indicate roughly 10 c of cooling from the early eocene climatic optimum 15 c through the end of the eocene minimum 5 c much of which took place in two comparatively short intervals at ca 52 and ca 41 ma many features of the isotope curves generated from this eocene shelf section are apparent in 18 o and 13 c data from the southern and global oceans including warm intervals that likely correspond to the early and middle eocene climatic optima eeco and meco a rapid middle eocene shift to much more positive values is the most signifi cant in the section and refl ects a drop to universally cooler temperatures in the late middle and late eocene that might also be associated with a short lived glacial advance however even using a somewhat depleted value for 18 o of seawater in the antarctic peninsular region average seymour island shelf water paleotemperatures did not reach freezing before the end of the eocene 13 c data similarly refl ect the documented middle eocene surface ocean enrichment followed by more negative values but depletion is much more pronounced on seymour island and persists for the remainder of the eocene suggesting a combination of upwelling metabolic effects and or atypical carbon cycling on the shelf in this region isotope data capture information about changes in the paleoenvironment that also had consequences for the biota as published paleontological records document marked change in the nature of terrestrial and marine biota at this time the fact that middle eocene cooling and biotic turnover in the peninsular region correspond well in time to the proposed initial opening of drake passage suggests that the formation of gateways in addition to changes in pco 2 had signifi cant consequences for the earth s climate system during the paleogene

evidence for an earliest oligocene ice sheet on the antarctic peninsula there is growing consensus that development of a semipermanent ice sheet on antarctica began at or near the eocene oligocene e o boundary beyond ice rafted debris in oceanic settings however direct evidence for a substantial ice sheet at this time has been limited and thus far restricted to east antarctica it is unclear where glacier ice first accumulated and how extensive it was on the antarctic continent in the earliest oligocene sediments at the top of the eocene marine shelf section on seymour island antarctic peninsula include glacial marine deposits and a lodgment till with clasts derived from a variety of rock units on the peninsula dinoflagellate biostratigraphy and strontium isotope stratigraphy indicate an age at or very close to the e o boundary glacier ice extending to sea level in the northern peninsula at this time suggests the presence of a regionally extensive west antarctica ice sheet and thus an even more dramatic response to the forcing factors that facilitated high latitude ice expansion in the earliest oligocene

eocene cooling linked to early flow across the tasmanian gateway the warmest global temperatures of the past 85 million years occurred during a prolonged greenhouse episode known as the early eocene climatic optimum 52 50 ma the early eocene climatic optimum terminated with a long term cooling trend that culminated in continental scale glaciation of antarctica from 34 ma onward whereas early studies attributed the eocene transition from greenhouse to icehouse climates to the tectonic opening of southern ocean gateways more recent investigations invoked a dominant role of declining atmospheric greenhouse gas concentrations e g co2 however the scarcity of field data has prevented empirical evaluation of these hypotheses we present marine microfossil and organic geochemical records spanning the early to middle eocene transition from the wilkes land margin east antarctica dinoflagellate biogeography and sea surface temperature paleothermometry reveal that the earliest throughflow of a westbound antarctic counter current began 49 50 ma through a southern opening of the tasmanian gateway this early opening occurs in conjunction with the simultaneous onset of regional surface water and continental cooling 2 4 c evidenced by biomarker and pollen based paleothermometry we interpret that the westbound flowing current flow across the tasmanian gateway resulted in cooling of antarctic surface waters and coasts which was conveyed to global intermediate waters through invigorated deep convection in southern high latitudes although atmospheric co2 forcing alone would provide a more uniform middle eocene cooling the opening of the tasmanian gateway better explains southern ocean surface water and global deep ocean cooling in the apparent absence of sub equatorial cooling

global cooling during the eocene oligocene climate transition about 34 million years ago earth s climate shifted from a relatively ice free world to one with glacial conditions on antarctica characterized by substantial ice sheets how earth s temperature changed during this climate transition remains poorly understood and evidence for northern hemisphere polar ice is controversial here we report proxy records of sea surface temperatures from multiple ocean localities and show that the high latitude temperature decrease was substantial and heterogeneous high latitude 45 degrees to 70 degrees in both hemispheres temperatures before the climate transition were 20 c and cooled an average of 5 c our results combined with ocean and ice sheet model simulations and benthic oxygen isotope records indicate that northern hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time

a novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids we propose a novel tracer for terrestrial organic carbon in sediments based on the analysis of tetraether lipids using high performance liquid chromatography mass spectrometry hplc ms analysis of terrestrial soil and peats shows that branched tetraether lipids are predominant in terrestrial environments in contrast to crenarchaeol the characteristic membrane lipid of non thermophilic crenarchaeota which is especially abundant in the marine and lacustrine environment based on these findings an index was developed the so called branched and isoprenoid tetraether bit index based on the relative abundance of terrestrially derived tetraether lipids versus crenarchaeol this bit index was applied to surface sediments from the angola basin where it was shown to trace the outflow of the congo river furthermore analyses of particulate organic matter from the north sea showed relatively higher bit indices in water column particulate organic matter near large river inputs a survey of globally distributed marine and lacustrine surface sediments shows that the bit index in these environments correlates with the relative fluvial input of terrestrial organic material making this index generally applicable the new proxy allows the rapid assessment of the fluvial input of terrestrial organic material in immature sediments up to 100 ma old

sedimentary record of caldera forming eruptions eocene challis volcanic field idaho large explosive eruptions and base level change by synsedimentary faulting controlled fluvial geometry in deposits 35 km downstream from the van horn peak cauldron complex idaho eruptions varied the volume and size of sediment load the major impact of large eruptions was a marked increase in the proportion of sand sized pyroclastic material from 42 to 93 smaller eruptions in contrast increased only the washload component following major eruptions the river developed into a multichannel system characterized by wide 75 m and shallow 0 5 m channels the sedimentary record of this system is a sheet sandstone with width thickness ratios ranging from 42 1 to 83 1 in the best exposed sandstone body the sheets comprise 86 sandstone with low amplitude stratification most of this is planar laminated sandstone with tabular geometry this laminated sheet assemblage is an unusual sedimentary accumulation for perennial rivers the assemblage represents accumulation under a combination of base level rise associated with faulting and increased sandy sediment loads produced by eruptions these factors created an environment conducive to rapid aggradation declining sandy sediment loads together with influx of fine ash mud sized sediment caused the river to change to a single channel system characterized by more stable and deep channels the sedimentary record of this system is the mudrock sandstone assemblage that has 46 overbank deposits with a significant mudrock fraction channel sandstone bodies in this assemblage are smaller sheets with width thickness ratios ranging from 8 1 to 25 1

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

a magneto and chemostratigraphically calibrated dinoflagellate cyst zonation of the early palaeogene south pacific ocean abstract investigation of the early palaeogene palaeoecological and palaeoclimatological evolution of the polar regions is hindered by the absence of calcite microfossils in sedimentary archives which are conventionally the main dating tool to overcome this problem we have generated large datasets of organic dinoflagellate cyst dinocyst assemblages from southern ocean shelf sediments over the past decade and we here calibrate these to the geomagnetic polarity time scale gpts using magnetostratigraphy and stable isotope stratigraphy this now for the first time allows a high resolution southern pacific ocean dinocyst zonation for the late palaeocene to late eocene 58 36 million years ago ma we compile published dinocyst chronologies from ocean drilling program odp hole 1171d on the south tasman rise hole 1172a d on the east tasman plateau and integrated ocean drilling program iodp hole u1356a on the wilkes land margin correlation to dinocyst zonations from new zealand lead to revisions of the magnetostratigraphic age model at holes 1171d and 1172a d stable carbon and oxygen isotope records reveal the stratigraphic location of the palaeocene eocene thermal maximum 56 ma and the middle eocene climatic optimum 40 ma respectively the resulting zonation consists of thirteen dinocyst zones calibrated to the geomagnetic polarity time scale gpts of vandenberghe et al 2012 which can likely be applied to the entire southern ocean finally we apply the revised stratigraphy to all published tex86 data a biomarker based proxy for sea surface temperature sst from odp site 1172 to assess long term climate evolution this shows that southwest pacific sst trends mimic the global compilation of benthic foraminiferal oxygen isotopes even better than previously appreciated

eocene circulation of the southern ocean was antarctica kept warm by subtropical waters 1 near the eocene s close 34 million years ago the climate system underwent one of the largest shifts in earth s history antarctic terrestrial ice sheets suddenly grew and ocean productivity patterns changed previous studies conjectured that poleward penetration of warm subtropical currents the east australian current eac in particular caused eocene antarctic warmth late eocene opening of an ocean gateway between australia and antarctica was conjectured to have disrupted the eac cooled antarctica and allowed ice sheets to develop here we reconstruct eocene paleoceanographic circulation in the tasmanian region using 1 biogeographical distributions of phytoplankton including data from recently drilled ocean drilling program leg 189 sites and 2 fully coupled climate model simulations we find that the eac did not penetrate to high latitudes and ocean heat transport in the region was not greater than modern our results do not support changes in thermal isolation as the primary driver of the eocene oligocene climatic transition

13c 18o isotope signatures and clumped isotope thermometry in foraminifera and coccoliths accurate constraints on past ocean temperatures and compositions are critical for documenting climate change and resolving its causes most proxies for temperature are not thermodynamically based appear to be subject to biological processes require regional calibrations and or are influenced by fluid composition as a result their interpretation becomes uncertain when they are applied in settings not necessarily resembling those in which they were empirically calibrated independent proxies for past temperature could provide an important means of testing and or expanding on existing reconstructions here we report measurements of abundances of stable isotopologues of calcitic and aragonitic benthic and planktic foraminifera and coccoliths relate those abundances to independently estimated growth temperatures and discuss the possible scope of equilibrium and kinetic isotope effects the proportions of 13c 18o bonds in these samples exhibits a temperature dependence that is generally similar to that previously been reported for inorganic calcite and other biologically precipitated carbonate containing minerals apatite from fish reptile and mammal teeth calcitic brachiopods and molluscs aragonitic coral and mollusks most species that exhibit non equilibrium 18o 16o 18o and 13c 12c 13c ratios are characterized by 13c 18o bond abundances that are similar to inorganic calcite and are generally indistinguishable from apparent equilibrium with possible exceptions among benthic foraminiferal samples from the arctic ocean where temperatures are near freezing observed isotope ratios in biogenic carbonates can be explained if carbonate minerals generally preserve a state of ordering that reflects the extent of isotopic equilibration of the dissolved inorganic carbon species

coexistence of three calcium carbonate polymorphs in the shell of the antarctic clam laternula elliptica 1 we analyzed shell cuts of five individuals of the antarctic bivalve laternula elliptica from three locations along the antarctic peninsula by means of confocal raman microscopy crm as well as electron microprobe emp the shell of l elliptica has been previously described as being composed of aragonite exclusively now crm mapping reveals that three polymorphs of calcium carbonate aragonite calcite and vaterite are present in the chondrophore region of the examined individuals annual shell growth layers continue through aragonite and vaterite suggesting simultaneous mineralization of both polymorphs spatially congruent emp scans showed that the calcium carbonate polymorph affects the distribution of magnesium and strontium within the chondrophore this is to our knowledge the first report of the coexistence of these three calcium carbonate polymorphs within the mineralized structures of a marine calcifying organism particularly the presence of vaterite is unexpected but shows striking similarities to some fish otoliths the strong effect of the calcium carbonate polymorph on trace element incorporation restrict the suitability of magnesium and strontium based proxies for the chondrophore area of l elliptica

the ocean circulation in the southern hemisphere and its climatic impacts in the eocene abstract opening of southern ocean gateways may have had a controlling influence on the evolution of global climate the largest step in the history of cenozoic climate from an eocene greenhouse toward the modern glaciated state is correlated with opening of a deep water connection between the southern indian and southern pacific oceans this study synthesizes results from previous work assesses the possibility that ocean heat transport was much greater than modern during the globally warm eocene and explores the sensitivity of polar climate to large changes in ocean heat transport the magnitudes of these sensitivities are compared with those due to greenhouse gas concentration changes we find that ocean heat transport was unlikely to have been sufficiently greater than modern during the eocene to explain the change in the climate specifically in order to have significantly affected antarctic climate ocean heat transport changes would have had to change by an order of magnitude much greater than the largest change produced in our simulations in coupled climate model simulations changes in co2 concentrations from 1120 to 560 ppm supported by proxy records lead to significant antarctic responses in the absence of ocean heat transport changes the results show that antarctic snow accumulation is primarily controlled by changes in summer temperature not precipitation and that snow did not remain on antarctica during summer months in eocene even at low greenhouse gas concentrations greenhouse gas concentration changes and subsequent processes such as ice albedo and weathering feedbacks were more likely to have been the primary cause of antarctic glaciation than ocean heat transport changes

carbonate clumped isotope bond reordering and geospeedometry carbonate clumped isotope thermometry is based on the preference of 13c and 18o to form bonds with each other at elevated temperatures such bond ordering is susceptible to resetting by diffusion of c and o through the solid mineral lattice this type of bond reordering has the potential to obscure primary paleoclimate information but could also provide a basis for reconstructing shallow crustal temperatures and cooling rates we determined arrhenius parameters for solid state reordering of c o bonds in two different calcites through a series of laboratory heating experiments we find that the calcites have different susceptibilities to solid state reordering reaction progress follows a first order rate law in both calcites but only after an initial period of non first order reaction that we suggest relates to annealing of nonequilibrium defects when the calcites are first heated to experimental temperature we show that the apparent equilibrium temperature equations or closure temperature equations for carbonate clumped isotope reordering are analogous dodson s equations for first order loss of daughter isotopes for each calcite the sensitivity of apparent equilibrium temperature to cooling rate is sufficiently high for inference of cooling rates within a factor of 5 or better for cooling rates ranging from tens of degrees per day to a few degrees per million years however because the calcites have different susceptibilities to reordering each calcite defines its own cooling rate apparent equilibrium temperature relationship the cooling rates of carrara marble inferred from carbonate clumped isotope geospeedometry are 10 6 10 3 degrees per annum and are in broad agreement with rates inferred from thermochronometric methods cooling rates for 13c depleted calcites from the late neoproterozoic doushantou cap carbonates in south china are on the order of 102 104 degrees per annum consistent with rapid cooling following formation of these calcites by a short lived hydrothermal event bristow et al 2011 nature v 474 p 68 71 most of the uncertainty in these estimates relates to uncertainty in arrhenius parameters for different calcites thus while the carbonate clumped isotope geospeedometer shows promise for recording cooling rates in settings and lithologies where other geospeedometers may not be applicable the uncertainty in cooling rate will be large without independent knowledge of the reordering kinetics of each study material thus the full potential of the method will only be realized if reordering kinetics can be accurately determined for each study material or predicted on the basis of mineral composition texture or other observable parameters

stable isotope and minor element proxies for eocene climate of seymour island antarctica 1 abundant and well preserved marine macrofossils on seymour island antarctica provide a valuable resource to establish paleoenvironmental conditions at high southern latitudes during the warm paleogene stable isotope minor element and 8 7 sr 8 6 sr compositions have been measured for the aragonite bivalve cucullaea from the eocene la meseta formation the 8 7 sr 8 6 sr stratigraphy suggests an early to late eocene age for the la meseta formation sea surface temperature estimates based on 1 8 o values range from 14 5 to 15 5 c in the early and middle eocene to 10 5 c in the late eocene high resolution sampling along growth structures provides estimates of seasonality in temperature which decrease considerably up section to address the relative contribution of temperature and ice volume or salinity to the 1 8 o record sr ca was measured and evaluated as a potential independent paleothermometer for cucullaea

a revised calibration of the clumped isotope thermometer abstract a growing number of materials and environmental settings are studied using the carbonate clumped isotope 47 thermometer the method has been applied in both biogenic and non biogenic carbonate systems in marine and terrestrial settings over a wide range of geological timescales the current 47 temperature calibration gives good temperature estimates for most biogenic materials however systematic biases are commonly observed at low temperatures in this study we report additional calibration data that covers a wider temperature range at more evenly distributed temperatures and are measured at higher analytical precision than the original calibration combining these data with the original calibration yields a 47 t relationship that is similar to the original calibration though slightly less steep 47 0 0526 0 0025 10 6 t 2 0 0520 0 0284 this revised calibration is in better agreement with biogenic carbonates including those grown at low temperatures the difference between the original and revised calibrations is significant for carbonates forming below 16 c or above 49 c 47 values of 0 68 and 0 56 additionally we include a comprehensive analysis of the sources of error associated with 47 measurements and estimated temperatures and recommend measurement strategies for obtaining the desired precision as an illustration we apply the revised calibration and uncertainty analysis to 3 previously published studies at low temperatures the revised calibration results in significant differences from the original calibration and hence affects the interpretation of the environmental signal recorded in light of our 47 errors analysis in cases where the temperature signals are small we find that replicate analyses are critical to identify a temperature signal

middle eocene climate cyclicity in the southern pacific implications for global ice volume we use a multiproxy approach to determine surface and bottom water temperatures off the coast of new zealand during the middle eocene and to constrain the 18o of seawater we use these data to place constraints on the size and variability of global ice sheets at that time the hampden section in south island is characterized by exceptionally well preserved micro fossils and clear sedimentary cyclicity providing a remarkable window into conditions at paleo latitude 55 s in the pacific ocean the cyclicity was studied in detail over a 4 m section corresponding to an interval of 70 k y ca 41 7 ma the sedimentary cycles are defined by fluctuations in the sand 63 m component occurring on a wavelength of 1 m corresponding to milankovitch scale frequency analyses of foraminifer oxygen isotopic 18 o and mg ca composition combined with tex86 analyses from organic carbon are used to generate records of seawater temperature and oxygen isotopic composition 18osw these indicate bottom water temperatures of 11 13 c and sea surface temperatures of 23 25 c with good agreement between the proxies temperature cyclicity with a magnitude of 1 5 c occurs in both surface and bottom waters approximately in phase with the sedimentary cycles estimates of 18osw have a mean value of 1 2 throughout the study section taken together the data suggest a largely ice free world with orbital scale cycles expressed as temperature and hydrological variation with little or no ice volume change

climate sensitivity to arctic seaway restriction during the early paleogene abstract the opening and closing of ocean gateways affects the global distribution of heat salt and moisture potentially driving climatic change on regional to global scales between 65 and 45 million years ago ma during the early paleogene exchange between the arctic and global oceans occurred through two narrow and shallow seaways the greenland norway seaway and the turgai strait sediments from the arctic ocean suggest that during this interval the surface ocean was warm brackish and episodically enabled the freshwater fern azolla to bloom the precise mechanisms responsible for the development of these conditions in the paleogene arctic remain uncertain here we show results from an isotope enabled atmosphere ocean general circulation model which indicate that northern hemisphere climate would have been very sensitive to the degree of oceanic exchange through the arctic seaways we also present modelled estimates of seawater and calcite 18o for the paleogene by restricting these seaways we simulate freshening of the surface arctic ocean to 6 psu and warming of sea surface temperatures by 2 c in the north atlantic and 5 10 c in the labrador sea our results may help explain the occurrence of low salinity tolerant taxa in the arctic ocean during the eocene and provide a mechanism for enhanced warmth in the north western atlantic we propose that the formation of a volcanic land bridge between greenland and europe could have caused increased ocean convection and warming of intermediate waters in the atlantic if true this result is consistent with the theory that bathymetry changes may have caused thermal destabilisation of methane clathrates and supports a tectonic trigger hypothesis for the paleocene eocene thermal maximum petm

oceanographic considerations for the application of the alkenone based paleotemperature u37k index in the gulf of california abstract alkenone concentrations were determined in sediment trap samples and surficial sediments collected from guaymas basin gulf of california to investigate the factors that control the relationship between the u37k index and sst the results from the sediment trap study reveal a positive correlation r2 0 5 between alkenone fluxes and satellite avhrr sea surface temperature sst and a strong correlation r2 0 9 between u37k and sst over an annual temperature range of 20 c although sst and u37k are tightly coupled throughout two upwelling seasons the relationship deviates from the expression developed by prahl et al 1988 at temperatures higher than 26 c the possible reasons for this deviation are varied but include the observed changes in the coccolithophore species assemblage and the evolution of the thermocline during periods of high sst the seasonal pattern of alkenone fluxes higher fluxes during warm periods observed throughout the 1996 to 1997 study period causes a bias in the annually averaged u37k record resulting in temperature estimates that are 1 c higher than the annual avhrr sst average furthermore the u37k ratios obtained from core top sediments indicate an additional 2 c warm bias in the sedimentary record that may be related to the lateral inputs of alkenones from other regions of the gulf these results highlight the importance of oceanographic processes in determining the alkenone temperature signal that is preserved in sediments after accounting for such effects u37k ratios from a box core were used to reconstruct a sst record extending back to the 18th century for the guaymas basin these results indicate a steady 2 c warming of the surface waters of the gulf from early 1700s to the 1950s followed by a rapid apparent 1 c cooling between the 1950s and the 1980s

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

temperature and salinity of the late cretaceous western interior seaway the western interior seaway wis was a shallow and expansive body of water that covered the central united states during the late cretaceous attempts to reconstruct temperatures in the seaway using the oxygen isotopic composition of biogenic carbonates have suffered from uncertainty in the oxygen isotopic composition of seawater 18 o w in the semi restricted basin we present new reconstructed temperature and 18 o w data from marine and estuarine environments in the wis and freshwater environments in wis source rivers derived from clumped isotope analyses of bivalve and gastropod shells we find temperatures of 5 21 c 18 o w values below contemporaneous gulf of mexico marine sites and a strong correlation between 18 o w and environmental setting we propose that decreasing 18 o w values reflect decreasing salinity driven by an increasing contribution of continental runoff using a two end member salinity 18 o w mixing model we estimate salinities of 29 35 psu practical salinity units for the deep marine 20 32 psu for the shallow marine and 11 26 psu for the estuarine environments of the wis new climate model simulations agree with reconstructed temperatures and salinities and suggest the presence of salinity driven stratification within the seaway

early paleogene temperature history of the southwest pacific ocean reconciling proxies and models we present a new multiproxy tex86 18o and mg ca marine temperature history for canterbury basin eastern new zealand that extends from middle paleocene to middle eocene including the paleocene eocene thermal maximum petm and early eocene climatic optimum eeco in light of concerns that proxy based sea surface temperature sst estimates are untenably warm for the southwest pacific during the eocene we review the assumptions that underlie the proxies and develop a preliminary paleo calibration for tex86 that is based on four multiproxy eocene records that represent an sst range of 15 34 c for the southwest pacific paleogene we show that tex86l exhibits the best fit with the eocene paleo calibration ssts derived from related proxies tex86h 1 tex86 exhibit a systematic warm bias that increases as tex86 values decrease a warm bias of 4 7 c where tex86 0 7 the tex86l proxy indicates that southwest pacific sst increased by 10 c from middle paleocene to early eocene with sst maxima of 26 28 c tropical during the petm and eeco and an sst minimum of 13 16 c cool warm temperate at the middle late paleocene transition 58 7 ma the base of the eeco is poorly defined in these records but the top is well defined in canterbury basin by a 2 5 c decrease in sst and bottom water temperature bwt in the latest early eocene 49 3 ma bwt falls from a maximum of 18 20 c in the eeco to 12 14 c in the middle eocene overall cooler temperatures are recorded in the mid waipara section which may reflect a deeper 500 m water depth and less neritic depositional setting compared with hampden and odp 1172 200 m water depth the high ssts and bwts inferred for the petm and eeco can be reconciled with eocene coupled climate model results if the proxies are biased towards seasonal maxima and the likely effect of a proto east australian current is taken into account

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

co2 driven ocean circulation changes as an amplifier of paleocene eocene thermal maximum hydrate destabilization changes in ocean circulation have been proposed as a trigger mechanism for the large coupled climate and carbon cycle perturbations at the paleocene eocene thermal maximum petm ca 55 ma an abrupt warming of oceanic intermediate waters could have initiated the thermal destabilization of sediment hosted methane gas hydrates and potentially triggered sediment slumps and slides in an ensemble of fully coupled atmosphere ocean general circulation model aogcm simulations of the late paleocene and early eocene we identify such a circulation driven enhanced intermediate water warming critically we find an approximate twofold amplification of atlantic intermediate water warming when co2 levels are doubled from 2x to 4x preindustrial co2 compared to when they are doubled from 1x to 2x this warming is largely focused on the equatorial and south atlantic and is driven by a significant reduction in deep water formation from the southern ocean this scenario is consistent with altered petm circulation patterns inferred from benthic carbon isotope data and the intensity of deep sea carbonate dissolution in the south atlantic the linkage between intermediate water warming and gas hydrate destabilization could provide an important feedback in the establishment of peak petm warmth

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

tropical sea temperatures in the high latitude south pacific during the eocene sea surface temperature sst estimates of 30 c from planktic foraminifera and archaeal membrane lipids in bathyal sediments in the canterbury basin new zealand support paleontological evidence for a warm subtropical to tropical climate in the early eocene high latitude 55 s southwest pacific such warm ssts call into question previous estimates based on oxygen isotopes and present a major challenge to climate modelers even under hypergreenhouse conditions 2240 ppm co2 modeled summer ssts for the new zealand region do not exceed 20 c

in situ produced branched glycerol dialkyl glycerol tetraethers in suspended particulate matter from the yenisei river eastern siberia abstract soil derived branched glycerol dialkyl glycerol tetraethers brgdgts in marine river fan sediments have a potential use for determining changes in the mean annual temperature mat and ph of the river watershed soils prior to their incorporation in marine sediments the compounds are transported to the marine system by rivers however emerging evidence suggests that the brgdgts in freshwater systems can be derived from both soil run off and in situ production the production of brgdgts in the river system can complicate the interpretation of the brgdgt signal delivered to the marine system therefore we studied the distribution of brgdgt lipids in suspended particulate matter spm of the yenisei river chromatographic improvements allowed quantification of the recently described hexamethylated brgdgt isomer characterized by having two methyl groups at the 6 6 instead of the 5 5 positions in an environmental dataset for the first time this novel compound was the most abundant brgdgt in spm from the yenisei its fractional abundance correlated well with that of the 6 methyl isomer of the hexamethylated brgdgt that contains one cyclopentane moiety the yenisei river watershed is characterized by large differences in mat 11 c as it spans a large latitudinal range 46 73 n which would be expected to be reflected in brgdgt distributions of its soils however the brgdgt distributions in its spm show little variation furthermore the reconstructed ph values are high compared to the watershed soil ph we therefore hypothesize that the brgdgts in the yenisei river spm are predominantly produced in situ and not primarily derived from erosion of soil this accounts for the absence of a change in the temperature signal as the river water temperature is more stable using a lake calibration the reconstructed temperature values agree with the mean summer temperatures mst recorded the brgdgts delivered to the sea by the yenisei river during this season are thus not soil derived possibly complicating the use of brgdgts in marine sediments for palaeoclimate reconstructions

a multi proxy approach to determine antarctic terrestrial palaeoclimate during the late cretaceous and early tertiary fossil wood is abundant throughout the cretaceous and tertiary sequences of the northern antarctic peninsula region the fossil wood represents the remains of the vegetation that once grew at the southern high palaeolatitudes at 59 62 s through the general decline in climate from the late cretaceous global warmth through to the mid eocene cool period prior to the onset of glaciation this study draws on the largest dataset ever compiled of antarctic conifer and angiosperm woods in order to derive clearer insights into the palaeoclimate parameters including mean annual temperature mean annual range in temperature cold month mean warm month mean mean annual precipitation are recorded the fossil wood assemblages have been analysed using anatomical physiognomic characteristics to determine the palaeoclimate variables from the coniacian campanian to the middle eocene these results are compared with data derived from coexistence analysis of the fossil floras composed of leaves wood and palynomorphs and published data based on leaf physiognomic characters these studies indicate a relatively warm and wet late cretaceous that becomes drier and cooler in the early paleocene and subsequently returns to warmer wetter conditions by the latest early paleocene during the eocene the climate becomes relatively cool and dry once again the discrepancies obtained from these two methods coupled with other published data are discussed in the context of the fluctuations in the temperatures of the surrounding oceans and global patterns of climate change

convection of north pacific deep water during the early cenozoic the history of deep water formation and abyssal flow is poorly known but important to establish in order to develop a better understanding of changes in oceanic mass heat salt and nutrient transport north atlantic high latitude regions currently are the dominant deep water producers but paleogeographic constraints proxy interpretations and physical models have suggested other modes for the past such as those characterized by high latitude pacific sources subtropical sources or widespread nonlocalized sources here we present new north pacific late cretaceous paleogene nd isotope data from fossil fish debris and detrital silicates combined with results of coupled climate model simulations to test these hypothesized circulation modes the data and model simulations support a circulation mode characterized by high latitude bipolar pacific convection deep convection in the north pacific and likely the south pacific was most intense during the relatively cool portion of the late cretaceous paleocene and waned prior to the peak global warmth of the early eocene ca 52 ma

dinoflagellate cysts of the la meseta formation middle to late eocene antarctic peninsula implications for biostratigraphy palaeoceanography and palaeoenvironment dinoflagellate cyst assemblages recovered from the la meseta formation cropping out in seymour island antarctic peninsula are studied herein and their distribution is compared with the biostratigraphic scheme available for the palaeogene of the southern ocean and other high latitude regions in this way the la meseta formation is dated as middle lutetian to priabonian 46 2 36 ma which differs from the age provided by other fossils isotopes and also with the magnetostratigraphic scheme recently performed for the unit the dinoflagellate cyst data support the proposal of ocean circulation patterns on the south american shelf prior to the opening of drake passage assemblages from the la meseta formation contain antarctic endemic taxa which are also dominant in several circum antarctic sites located south of 45 s their distribution reflects an ocean circulation scheme with wide clockwise gyres surrounding antarctica that were disrupted as a consequence of the deepening and definitive apertures of the tasmanian gateway and drake passage towards the eocene oligocene transition the palaeoenvironmental inference based on the s d ratio sporomorphs versus dinoflagellate cysts and the p g ratio peridinioid versus gonyaulacoid dinoflagellate cysts suggests an overall trend through the section from marine dominated assemblages with poorly productive waters in the lower part of the section to more terrestrially dominated assemblages with increasing productivity in the upper part of the unit reflecting a shallowing trend to the top

evidence for deep water production in the north pacific ocean during the early cenozoic warm interval the deep ocean circulation is responsible for a significant component of global heat transport in the present mode of circulation deep waters form in the north atlantic and southern oceans where surface water becomes sufficiently cold and dense to sink polar temperatures during the warmest climatic interval of the cenozoic era approximately 65 to 40 million years myr ago were significantly warmer than today and this may have been a consequence of enhanced oceanic heat transport however understanding the relationship between deep ocean circulation and ancient climate is complicated by differences in oceanic gateways which affect where deep waters form and how they circulate here i report records of neodymium isotopes from two cores in the pacific ocean that indicate a shift in deep water production from the southern ocean to the north pacific approximately 65 myr ago the source of deep waters reverted back to the southern ocean 40 myr ago the relative timing of changes in the neodymium and oxygen isotope records indicates that changes in cenozoic deep water circulation patterns were the consequence not the cause of extreme cenozoic warmth

benthic foraminiferal mg ca paleothermometry a revised core top calibration core top samples from different ocean basins have been analyzed to refine our current understanding of the sensitivity of benthic foraminiferal calcite magnesium calcium mg ca to bottom water temperatures bwt benthic foraminifera collected from hawaii little bahama bank sea of okhotsk gulf of california ne atlantic ceara rise sierra leone rise the ontong java plateau and the southern ocean covering a temperature range of 0 8 to 18 c were used to revise the cibicidoides mg ca temperature calibration the mg ca bwt relationship of three common cibicidoides species is described by an exponential equation mg ca 0 867 0 049 exp 0 109 0 007 bwt stated errors are 95 ci the temperature sensitivity is very similar to a previously published calibration however the revised calibration has a significantly different preexponential constant resulting in different predicted absolute temperatures we attribute this difference in the preexponential constant to an analytical issue of accuracy some genera notably uvigerina show apparently lower temperature sensitivity than others suggesting that the use of constant offsets to account for vital effects in mg ca may not be appropriate downcore mg ca reproducibility as determined on replicate foraminiferal samples is typically better than 0 1 mmol mol 1 2 s e thus considering the errors associated with the cibicidoides calibration and the downcore reproducibility bwt may be estimated to within 1 c application of the revised core top mg ca bwt data to cenozoic foraminiferal mg ca suggests that seawater mg ca was not more than 35 lower than today in the ice free ocean at 50 ma

origins of archaeal tetraether lipids in sediments insights from radiocarbon analysis abstract understanding the supply and preservation of glycerol dibiphytanyl glycerol tetraethers gdgts in marine sediments helps inform their use in paleoceanography compound specific radiocarbon measurements of sedimentary alkenones from multiple environments have been used to gain insight into processes that affect u 37 k paleotemperature reconstructions similar analyses are warranted to investigate how analogous processes affecting gdgts impact tex 86 paleotemperatures here we present radiocarbon measurements on individual gdgts from bermuda rise and santa monica basin sediments and discuss the results in the context of previous studies of co depositional alkenones and foraminifera the 14 c contents of gdgts and planktonic foraminifera in bermuda rise are very similar suggesting a local source and tex 86 derived temperatures agree more closely with foraminiferal temperatures than do u 37 k temperatures in contrast gdgts in santa monica basin are depleted in 14 c relative to both alkenones and foraminifera and tex 86 temperatures agree poorly with known surface water values we propose three possible factors that could explain these results i gdgts may be labile relative to alkenones during advective transport through oxic waters ii archaeal production deep in the water column may contribute 14 c depleted gdgts to sediments and iii some gdgts also may derive from sedimentary archaeal communities each of these three processes is likely to occur with varying relative importance depending on geographic location the latter two may help to explain why tex 86 temperature reconstructions from santa monica basin do not appear to reflect actual sea surface temperatures terrigenous gdgts are unlikely to be major contributors to bermuda rise or santa monica basin sediments based on values of the bit index the results also indicate that the crenarchaeol regioisomer is governed by processes different from other gdgts individual measurements of the crenarchaeol regioisomer are significantly depleted in 14 c relative to co occurring gdgts indicating an alternative origin for this compound that presently remains unknown re examination of the contribution of crenarchaeol regioisomer to the tex 86 index shows that it is a significant influence on the sensitivity of temperature reconstructions

eurasian snow cover variability and northern hemisphere climate predictability we present observational evidence demonstrating dynamic interactions and feedbacks between multi seasonal snow cover and winter time circulation anomalies over mid high latitudes the cooling effect of snow cover is associated with a strengthened and more expansive siberian high with more frequent topographically constrained intrusions west and north early season snow cover variability leads to altered general circulation patterns consistent with the dominant mode of winter variability observed in the northern hemisphere troposphere the implications of the surface atmosphere coupling for seasonal to interannual predictability are also discussed

timing and nature of the deepening of the tasmanian gateway 1 tectonic changes that produced a deep tasmanian gateway between australia and antarctica are widely invoked as the major mechanism for antarctic cryosphere growth and antarctic circumpolar current acc development during the eocene oligocene e o transition 34 33 ma ocean drilling program odp leg 189 recovered near continuous marine sedimentary records across the e o transition interval at four sites around tasmania these records are largely barren of calcareous microfossils but contain a rich record of siliceous and organic walled marine microfossils in this study we integrate micropaleontological sedimentological geochemical and paleomagnetic data from site 1172 east tasman plateau to identify four distinct phases a d in the e o tasmanian gateway deepening that are correlative among odp leg 189 sites phase a prior to 35 5 ma minor initial deepening characterized by a shallow marine prodeltaic setting with initial condensation episodes phase b 35 5 33 5 ma increased deepening marked by the onset of major glauconitic deposition and inception of energetic bottom water currents phase c 33 5 30 2 ma further deepening to bathyal depths with episodic erosion by increasingly energetic bottom water currents phase d 30 2 ma establishment of stable open ocean warm temperate oligotrophic settings characterized by siliceous carbonate ooze deposition our combined evidence indicates that this early oligocene tasmanian gateway deepening initially produced an eastward flow of relatively warm surface waters from the australo antarctic gulf into the southwestern pacific ocean this proto leeuwin current fundamentally differs from previous regional reconstructions of eastward flowing cool water e g a proto acc during the early oligocene and thereby represents an important new constraint for reconstructing regional to global scale dynamics for this major global change event

alkenones and alkenes in surface waters and sediments of the southern ocean implications for paleotemperature estimation in polar regions abstract the concentration of c37 c39 long chain alkenones and alkenes were determined in surface water and surface sediment samples from the subpolar waters of the southern ocean distributions of these compounds were similar in both sample sets indicating little differential degradation between or within compound classes the relative amounts of the tri to tetra unsaturated c37 alkenones increased with increasing temperature for temperatures below 6 c similar to the di and tri unsaturated c37 alkenones the c37 di tri and tetra unsaturated methyl alkenones are used in paleotemperature calculations via the u37k and the u37k ratios in these datasets the relative abundances of the c37 2 and the c37 3 alkenones as a proportion of the total c37 alkenones were opposite and strongly related to temperature the latter with more scatter but the abundance of the c37 4 alkenone showed no relationship with temperature the original definition of u37k includes the abundance of 37 4 in both the numerator and denominator and thus it is perhaps not surprising that there is considerable scatter in the values obtained for u37k at low temperatures of the two we suggest that u37k is the better parameter for use in paleotemperature estimations even in cold locations u37k values in the sediments fall on virtually the same regression line obtained for the water column samples of sikes and volkman 1993 indicating that their calibration is suitable for use in southern ocean sediments the comparison of water column data with sedimentary temperature estimates suggests that the alkenone distributions are dominated by contributions from the summer when the biomass of emiliania huxleyi and presumably flux to the sediment is expected to be high

environmental change across the paleocene eocene transition from eastern new zealand a marine palynological approach abstract recent improvements in the resolution and calibration of dinoflagellate cyst dinocyst bioevents across the paleocene eocene p e transition in new zealand allow better understanding of the relation between dinocyst variations and environmental change in southern mid high latitudes during this greenhouse climate combining information from land spore pollen assemblages with coeval dinocyst records allows evaluation of plant changes in a marine based timeframe palynological associations at tawanui and moeraki hampden eastern new zealand fluctuate across the p e transition and local palynological phases are recognized the onset of major fluctuations in dinocyst assemblages coincide with the intense warmth and excess carbon of the initial eocene thermal maximum ietm changes in sea surface temperature sst appear to have been the main environmental factor that affected dinoflagellates short lived intervals of higher ssts suggested by a high relative abundance of the apectodinium complex are seen during the ietm and lower eocene abundant cysts of probable heterotrophic dinoflagellates suggest surface waters remained relatively eutrophic for up to 0 5 myr after the onset of the ietm perhaps in response to enhanced terrigenous input related to changes in the character and pattern of continental weathering in contrast to dinocysts spore pollen assemblages suggest plant communities remained rather stable across the p e transition vegetation was dominated by a mesothermal conifer dominated multistratal rainforest and low latitude nypa mangroves were established by the uppermost paleocene plants in this region show no clear response to the ietm and the predominant vegetation change may have occurred at least 1 5 myr later characterized by an increase in mesothermal megathermal angiosperm plants

quasi static eocene oligocene climate in patagonia promotes slow faunal evolution and mid cenozoic global cooling abstract new local regional climatic data were compared with floral and faunal records from central patagonia to investigate how faunas evolve in the context of local and global climates oxygen isotope compositions of mammal fossils between c 43 and 21 ma suggest a nearly constant mean annual temperature of 16 3 c consistent with leaf physiognomic and sea surface studies that imply temperatures of 16 18 c carbon isotopes in tooth enamel track atmospheric 13 c but with a positive deviation at 27 2 ma and a strong negative deviation at 21 ma combined with paleosol characteristics and reconstructed leaf area indices rlais these trends suggest aridification from 45 ma c 1200 mm yr to 43 ma c 450 mm yr quasi constant map until at least 31 ma and an increase to 800 mm yr by 21 ma comparable map through most of the sequence is consistent with relatively constant floral compositions rlai and leaf physiognomy abundance of palms reflects relatively dry adapted lineages and greater drought tolerance under higher p co2 pedogenic carbonate isotopes imply low p co2 430 300 ppmv at the initiation of the eocene oligocene climatic transition arid conditions in patagonia during the late eocene through oligocene provided dust to the southern ocean enhancing productivity of silicifiers drawdown of atmospheric co 2 and protracted global cooling as the antarctic circumpolar current formed and earth cooled wind speeds increased across patagonia providing more dust in a positive climate feedback high tooth crowns hypsodonty and ever growing teeth hypselodonty in notoungulates evolved slowly and progressively over 20 ma after initiation of relatively dry environments through natural selection in response to dust ingestion a ratchet evolutionary model may explain protracted evolution of hypsodonty in which small variations in climate or dust delivery in an otherwise static environment drive small morphological shifts that accumulate slowly over geologic time

evolution of early cenozoic marine temperatures the equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals late paleocene early eocene early middle eocene late eocene and early oligocene paleotemperatures are calculated using standard oxygen isotope temperature equations with adjustments to account for 1 variations in sea water 18o related to changes in global ice volume over time and 2 latitudinal gradients in surface water 18o these reconstructions indicate that sea surface temperatures sst of the southern oceans in the early eocene were as high as 15 c whereas temperatures during the late paleocene and early middle eocene reached maximum levels of 10 12 c by the late eocene and early oligocene high latitude sst had declined to 6 and 4 c respectively for most of the early paleogene low latitude sub tropical temperatures remained constant and well within the range of holocene temperatures 24 ndash 25 c but by the late eocene and early oligocene declined to values in the range of 18 to 22 c the late paleogene apparent decline in tropical temperatures however might be artificial because of dissolution of near surface foraminifera tests which biased sediment assemblages toward deeper dwelling foraminifera moreover according to recent plate reconstructions it appears that the majority of sites upon which the late eocene and early oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling global deepwater temperature on average paralleled southern ocean sst for most of the paleogene we speculate based on the overall timing and character of marine sea surface temperature variation during the paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high latitude warmth of the early eocene

effect of the deepening of the tasman gateway on the global ocean 1 we examine the effect of the deepening of the tasman seaway at the end of the eocene in a climate model with realistic late eocene bathymetry and winds for this we have constructed an eocene numerical model based on the university of victoria climate model with wind forcing derived from a fully coupled eocene simulation the model climate state is characterized by an oceanic meridional overturning circulation moc involving southern hemisphere sinking and a northward atmospheric moisture transport across the equator the deepening of the tasman seaway in the presence of an open drake passage and the associated establishment of the antarctic circumpolar current acc have a limited climatic impact on antarctica nonetheless the antarctic deep sinking regions cool sufficiently to lead to a global deep ocean cooling of 3 c no initiation of northern component water is found indicating that this may require the development of a more mature acc previous studies suggest that the ross sea gyre cools the east coast of australia and expected the deepening of the tasman seaway to lead to a warming east of australia due to the introduction of warmer water from the australo antarctic gulf we here find that this warming is limited to close to the australian coast and that widespread cooling prevails further off shore

maceral total organic carbon and palynological analyses of ross ice shelf project site j9 cores analyses of macerals and total organic carbon indicate that the low organic content of core sediments from ross ice shelf project site j9 has been selectively reduced further probably by postdepositional submarine oxidation palynological analysis revealed a reworked paleogene dinocyst flora of low diversity the transantarctic flora this constitutes the most southerly dinocyst flora reported thus far the antarctic distribution of the transantarctic flora supports the existence of a transantarctic strait during the paleogene the j9 sporomorph assemblage also is reworked and paleogene in age

the enigma of oligocene climate and global surface temperature evolution falling atmospheric co2 levels led to cooling through the eocene and the expansion of antarctic ice sheets close to their modern size near the beginning of the oligocene a period of poorly documented climate here we present a record of climate evolution across the entire oligocene 33 9 to 23 0 ma based on tex86 sea surface temperature sst estimates from southwestern atlantic deep sea drilling project site 516 paleolatitude 36 s and western equatorial atlantic ocean drilling project site 929 paleolatitude 0 combined with a compilation of existing sst records and climate modeling in this relatively low co2 oligocene world 300 to 700 ppm warm climates similar to those of the late eocene continued with only brief interruptions while the antarctic ice sheet waxed and waned ssts are spatially heterogenous but generally support late oligocene warming coincident with declining atmospheric co2 this oligocene warmth especially at high latitudes belies a simple relationship between climate and atmospheric co2 and or ocean gateways and is only partially explained by current climate models although the dominant climate drivers of this enigmatic oligocene world remain unclear our results help fill a gap in understanding past cenozoic climates and the way long term climate sensitivity responded to varying background climate states

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

terrestrial cooling in northern europe during the eocene oligocene transition geochemical and modeling studies suggest that the transition from the greenhouse state of the late eocene to the icehouse conditions of the oligocene 34 33 5 ma was triggered by a reduction of atmospheric pco2 that enabled the rapid buildup of a permanent ice sheet on the antarctic continent marine records show that the drop in pco2 during this interval was accompanied by a significant decline in high latitude sea surface and deep ocean temperature and enhanced seasonality in middle and high latitudes however terrestrial records of this climate transition show heterogeneous responses to changing pco2 and ocean temperatures with some records showing a significant time lag in the temperature response to declining pco2 we measured the 47 of aragonite shells of the freshwater gastropod viviparus lentus from the solent group hampshire basin united kingdom to reconstruct terrestrial temperature and hydrologic change in the north atlantic region during the eocene oligocene transition our data show a decrease in growing season surface water temperatures 10 c during the eocene oligocene transition corresponding to an average decrease in mean annual air temperature of 4 6 c from the late eocene to early oligocene the magnitude of cooling is similar to observed decreases in north atlantic sea surface temperature over this interval and occurs during major glacial expansion this suggests a close linkage between atmospheric carbon dioxide concentrations northern hemisphere temperature and expansion of the antarctic ice sheets

extremely high sea surface temperatures at low latitudes during the middle cretaceous as revealed by archaeal membrane lipids the middle cretaceous 125 88 ma greenhouse world was characterized by high atmospheric co 2 levels the general absence of polar ice caps and much higher global temperatures than at present both 1 8 o based and model based temperature reconstructions indicate extremely high sea surface temperatures ssts at high latitudes however there are a number of uncertainties with sst reconstructions based on 1 8 o isotope data of foraminifera due to diagenetic overprinting effects and tenuous assumptions with respect to the 1 8 o value of cretaceous seawater the paleoecology of middle cretaceous marine organisms and seawater ph here we applied a novel sst proxy i e text tetraether index of 86 carbon atoms based on the membrane lipids of marine crenarchaeota derived from middle cretaceous sedimentary rocks deposited at low latitudes the text proxy indicates that tropical ssts in the proto north atlantic were at 32 36 c during the early albian and late cenomanian early turonian this finding agrees with sst estimates based on 1 8 o paleothermometry of well preserved foraminifera as well as global circulation model calculations the text proxy indicates cooler ssts 27 32 c for the equatorial pacific during the early aptian which is in agreement with sst estimates based on 1 8 o paleothermometry

glacial interglacial temperature variations in soreq cave speleothems as recorded by clumped isotope thermometry clumped isotope thermometry is based on analyzing mass 47 in co2 extracted from carbonates and uses the tracer mass 47 anomaly 47 47 is defined as the deviation of r47 from that expected for a random distribution of isotopologues and reflects a temperature dependent preference of 13c and 18o to create a bond with each other in co2 or in the carbonate lattice being an internal characteristic of the carbonate mineral it is independent of the isotopic composition of the water in which equilibrium precipitation of the carbonate occurs and can therefore be used to independently determine carbonate growth temperatures this work provides a first examination of the applicability of clumped isotopes thermometry to reconstructing the growth temperatures of speleothems by examining the glacial interglacial variations of the 47 values of speleothem carbonates from soreq cave israel the results indicate that the last glacial maximum temperatures were 6 7 c colder than modern day temperature and a sample at 56 ky bp was 3 c colder than the modern early holocene temperatures were slightly above modern day and late holocene temperatures were slightly below modern day these temperature variations are similar to those previously estimated for eastern mediterranean sea surface water cave water was 18o depleted in the holocene compared to modern day by 0 6 1 and 1 1 more enriched in the last glacial maximum comparison of these cave water 18o values with fluid inclusion d values indicated a late holocene d excess value within the range of modern rainfall implying not vert similar45 relative humidity last glacial maximum and early holocene d excess values were significantly lower suggesting relative humidity of not vert similar60 and not vert similar70 respectively the temperatures reported in this study were empirically corrected for a non equilibrium artifact observed in a modern speleothem the similarity of the temperature variations obtained here to other independent records in the region suggests that the 47 temperature calibration slope observed in inorganic synthetic calcite and marine organisms may also be applied in speleothems but the offset observed in modern temperature suggests that the intercept is different so that a separate calibration is needed for accurate absolute temperature reconstruction using speleothem clumped isotopes similar examination of additional caves would be necessary to determine whether such empirical correction can be generally applied or is it a unique characteristic of soreq cave

early permian seasonality from bivalve δ18o and implications for the oxygen isotopic composition of seawater oxygen isotope values of sequentially microsampled accretionary carbonate from the thick shelled calcitic bivalve eurydesma from the early permian of southeastern australia vary seasonally over 6 yr of growth paleotemperature constraints derived from coeval glendonite and ice rafted clasts in combination with published biome data indicate near freezing winter conditions however paleotemperatures calculated from oxygen isotope data are too warm unless the 18 o value of seawater approached 4 associated stenohaline brachiopods and lack of covariance with 13 c argue against significantly reduced salinity and published 18 o data from across australia suggest that conditions recorded by this bivalve were typical of the gondwanan high latitudes the negative 18 o value of seawater implied by these data reflects in part the expected meridional gradient in marine seawater composition related to latitudinal variation in evaporation and precipitation in permian oceans but is also consistent with previous suggestions of a secular increase in the oxygen isotopic composition of ocean water through the phanerozoic

burial diagenesis and pore fluid evolution in a mesozoic back arc basin the marambio group vega island antarctica upper cretaceous shallow marine sediments from vega island antarctica contain five major authigenic phases glauconite pyrite a zeolite mineral of the clinoptilolite heulandite group chlorite and calcite the framework sediment composition changes from quartzose at the base of the measured succession to volcaniclastic at the top the petrogenesis of individual samples reflects the local controls on diagenesis of depositional environment and sediment composition combined with the effects of burial to no more than 1 km calcite cements are the most abundant precipitates marine carbonate cements include acicular and other fringing cements that commonly are present within bioclasts early burial micritic to sparry calcite cements include both concretionary and nonconcretionary forms burial calcites occlude residual porosity replace detrital grains and form veins with fibrous and cone in cone textures the stable isotope composition of the carbonate cements is very variable with delta 18 o ranging from 0 60 per thousand to 19 93 per thousand pdb and delta 13 c of 1 33 per thousand to 28 09 per thousand pdb the stable isotope data reflect the initial conditions of mineral precipitation in oxic and anoxic marine pore waters together with the effects of subsequent fluid rock interaction through both recrystallization and cementation the latest precipitates thought to have been formed during over pressuring define a vertical field for burial calcite on an isotope cross plot suggesting that late fluids responsible for cementation and alteration of earlier precipitates had negative delta 18 o and contained carbon with variable delta 13 c the oxygen values are compatible with either influx of high latitude meteoric water or intense fluid rock interaction with reactive volcanic detritus or a combination of the two processes the very variable carbon signatures probably reflect dissolution of bioclasts and earlier diagenetic precipitates only by identifying possible end member compositions for both early and late diagenetic precipitates can most of the isotopic data be interpreted correctly

environmental forcings of paleogene southern ocean dinoflagellate biogeography 1 despite warm polar climates and low meridional temperature gradients a number of different high latitude plankton assemblages were to varying extents dominated by endemic species during most of the paleogene to better understand the evolution of paleogene plankton endemism in the high southern latitudes we investigate the spatiotemporal distribution of the fossil remains of dinoflagellates i e organic walled cysts dinocysts and their response to changes in regional sea surface temperature sst we show that paleocene and early eocene 65 50 ma southern ocean dinocyst assemblages were largely cosmopolitan in nature but that a distinct switch from cosmopolitan dominated to endemic dominated assemblages the so called transantarctic flora occurred around the early middle eocene boundary 50 ma the spatial distribution and relative abundance patterns of this transantarctic flora correspond well with surface water circulation patterns as reconstructed through general circulation model experiments throughout the eocene we quantitatively compare dinocyst assemblages with previously published tex86 based sst reconstructions through the early and middle eocene from a key locality in the southwest pacific ocean odp leg 189 site 1172 on the east tasman plateau we conclude that the middle eocene onset of the proliferation of the transantarctic flora is not linearly correlated with regional sst records and that only after the transantarctic flora became fully established later in the middle eocene possibly triggered by large scale changes in surface ocean nutrient availability were abundances of endemic dinocysts modulated by regional sst variations

the climate of the late cretaceous new insights from the application of the carbonate clumped isotope thermometer to western interior seaway macrofossil abstract we apply the carbonate clumped isotope thermometer 47 to macrofossils from the baculites compressus 73 5 ma and the hoploscaphites nebrascensis 67 ma ammonite zones of the western interior seaway wis of north america and nearby coeval terrestrial and open marine environments the carbonate clumped isotope thermometer is based on a single phase isotope exchange equilibrium that promotes the clumping of two heavy isotopes together within a single carbonate molecule as temperature decreases due to the thermometer s isotopic independence from water coupled measurements of 47 and the bulk oxygen isotopic composition of a carbonate 18 o c enable the reconstruction of both paleotemperature and the isotopic composition of the water in which the organisms grew before applying the technique to the aragonite shells of fossil marine organisms mostly ammonites but also some gastropods bivalves and one belemnite we measure the clumped isotopic composition of modern nautilus and cuttlefish two of the nearest living relatives to the cretaceous ammonites modern cephalopods exhibit disequilibrium isotope effects with respect to 47 but not 18 o c therefore a simple correctional scheme is applied to the late cretaceous macrofossil data before reconstructing paleotemperatures diagenesis is also assessed by visual preservation and previously measured sr concentrations cochran et al 2003 temperatures reconstructed for the late cretaceous western interior seaway range from 16 4 3 5 c for an offshore interior seaway environment from the h nebrascensis zone to 24 2 0 4 c for the b compressus ammonite zone the seaway itself has an isotopic composition of approximately 1 relative to vsmow the expectation for an ice free global ocean average while a nearby freshwater environment has an isotopic composition approaching 20 we compare the attributes of the reconstructed climate to predictions based on late cretaceous climate models and previous reconstructions of the seaway and also assess the sensitivity of our results to the modern cephalopods correction by comparisons to suitable modern analogs finally our clumped isotope data are consistent with cooling between the late campanian and maastrichtian as also seen in benthic foraminfera 18 o