could early cenozoic thermohaline circulation have warmed the poles the paleocene and eocene epochs provide examples of oceanographic conditions when the earth had a stable climate much warmer than that of the modern world lower cenozoic sediments thus provide a way to investigate how oceanographic processes might respond to extreme warming because high latitude sea surface temperatures were significantly warmer during the early cenozoic while tropical sea surface temperatures were similar to or somewhat less than modern there may have been a much higher poleward oceanic heat transport at that time shackleton and boersma 1981 barron 1987 sloan et al 1995 here i develop a simple ocean thermohaline model to demonstrate that poleward oceanic heat transport could strongly warm the polar regions only if the strength of vertical mixing vertical eddy diffusion in the oceans is sensitive to changes in oceanic density structure if this is true the early cenozoic oceans because they had significantly less density stratification could have had a thermohaline circulation as much as 3 times as strong as that of the modern ocean despite reduced temperature gradients the model also predicts that an optimum bottom water temperature exists for maximum poleward heat transport continued warming of the earth does not continue to increase oceanic heat transport to the poles the hypothesized sensitivity of oceanic vertical mixing to the density gradient should provide a positive feedback to both the transition to ice ages and to a future transition out of them a test of the sensitivity of vertical eddy diffusion to density gradients can be studied through map and depth transects in the horizontal direction high vertical diffusion would be marked by relatively strong bottom water temperature gradients away from bottom water source regions in the vertical direction high vertical diffusion should be indicated by very small temperature gradients

tropical sea surface temperature reconstruction for the early paleogene using mg ca ratios of planktonic foraminifera 1 to understand the climate dynamics of hypothesized past greenhouse intervals it is essential to constrain tropical sea surface temperatures sst yet existing proxy records give conflicting results here we present the first mg ca based study of pre quaternary sst and investigate early paleogene late paleocene through late middle eocene 58 6 39 8 ma tropical temperatures using planktonic foraminifera belonging to the genus morozovella from ocean drilling program site 865 on allison guyot western central equatorial pacific ocean calcification temperatures similar to or warmer than modern tropical sst are calculated using a range of assumptions regarding diagenesis temperature calibration and seawater mg ca long term warming is observed into the early eocene 54 8 49 0 ma with peak sst between 51 and 48 ma and rapid cooling of 4 c beginning at 48 ma these findings are inconsistent with the 18o based sst previously estimated for this site

assessment of grain scale homogeneity and equilibration of carbon and oxygen isotope compositions of minerals in carbonate bearing metamorphic rocks by ion microprobe abstract nineteen samples of metamorphosed carbonate bearing rocks were analyzed for carbon and oxygen isotope ratios by ion microprobe with a 5 15 m spot three from a regional terrain and 16 from five different contact aureoles contact metamorphic rocks further represent four groups calc silicate marble and hornfels 6 brucite marble 2 samples that contain a reaction front 4 and samples with a pervasive distribution of reactants and products of a decarbonation reaction 4 the average spot to spot reproducibility of standard calcite analyses is 0 37 2 standard deviations sd for 18 o and 0 71 for 13 c ten or more measurements of a mineral in a sample that has uniform isotope composition within error of measurement can routinely return a weighted mean with a 95 confidence interval of 0 09 0 16 for 18 o and 0 10 0 29 for 13 c using a difference of 6sd as the criterion only four of 19 analyzed samples exhibit significant intracrystalline and or intercrystalline inhomogeneity in 13 c at the 100 500 m scale with differences within individual grains up to 3 7 measurements are consistent with carbon isotope exchange equilibrium between calcite and dolomite in five of six analyzed samples at the same scale because of relatively slow carbon isotope diffusion in calcite and dolomite differences in 13 c can survive intracrystalline homogenization by diffusion during cooling after peak metamorphism and likely represent the effects of prograde decarbonation and infiltration all but 2 of 11 analyzed samples exhibit intracrystalline differences in 18 o up to 9 4 intercrystalline inhomogeneity in 18 o up to 12 5 and or disequilibrium oxygen isotope fractionations among calcite dolomite calcite quartz and calcite forsterite pairs at the 100 500 m scale inhomogeneities in 18 o and 13 c are poorly correlated with only a single mineral dolomite in a single sample exhibiting both because of relatively rapid oxygen isotope diffusion in calcite intracrystalline inhomogeneities in 18 o likely represent partial equilibration between calcite and fluid during retrograde metamorphism calcite is in oxygen isotope exchange equilibrium with forsterite in one of four analyzed samples in equilibrium with dolomite in none of six analyzed samples and in equilibrium with quartz in neither of two analyzed samples there are no samples of contact metamorphic rock with analyzed reactants and products of an arrested metamorphic reaction that are in oxygen isotope equilibrium with each other the degree of departure from equilibrium in analyzed samples is variable and is often related at least in part to alteration of 18 o of calcite during retrograde fluid rock reaction in situ sub grain scale carbon and oxygen isotope analyses of minerals are advisable in the common applications of stable isotope geochemistry to metamorphic petrology correlation of sub mm scale stable isotope data with imaging will lead to improved understanding of reaction kinetics reactive fluid flow and thermal histories during metamorphism

effects of diagenesis on the isotopic record of late paleogene tropical sea surface temperatures abstract oxygen isotope records of planktonic foraminifera indicate that late eocene and oligocene tropical sea surface temperatures were as much as 8 c lower than present at a time when high latitude sea surface temperatures were higher than present using a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate the effects of diagenesis on bulk carbonate 18 o records for the cenozoic are quantified for four tropical sites most of the observed variations in measured 18 o values at all sites can be accounted for by diagenetic effects there are no systematic trends that support substantial variations in tropical sea surface temperatures beyond diagenetic effects with the possible exception of the early eocene for which the data are consistent with slightly higher sea surface temperatures reconstructions based on oxygen isotope records of planktonic foraminifera which indicate cooler tropical sea surface temperatures for the eocene and oligocene may be artifacts of diagenetic recrystallization as such records are particularly sensitive to diagenetic effects

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

planktonic foraminiferal biostratigraphy and mechanisms in the extinction of morozovella in the late middle eocene the muricate planktonic foraminiferal genera morozovella and acarinina were abundant and diverse during the upper palaeocene to middle eocene and dominated the tropical and subtropical assemblages a significant biotic turnover in planktonic foraminifera occurred in the latest middle eocene with a notable reduction in the acarininid lineage and the extinction of the morozovellids these genera are extensively employed as palaeoclimatic and biostratigraphic markers and therefore this turnover episode is an important event in the record of the cenozoic planktonic foraminifera sediments from the western north atlantic ocean drilling program site 1052 were examined in order to investigate these extinction events in terms of both timing and mechanisms biostratigraphic events of the middle and late eocene have been examined with a sampling resolution of approximately 3 kyr these have been calibrated to the magneto and astrochronology to accurately define the timing of key biostratigraphic events particularly the extinction of morozovella spinulosa which is a distinct biomarker for late middle eocene sediments high resolution biostratigraphy reveals that the extinctions in the muricate group occurred in a stepwise form the large acarininids acarinina praetopilensis terminate 10 kyr prior to the extinction of m spinulosa and small acarininids acarinina medizzai and acarinina echinata continue into the upper eocene high resolution stable isotope analyses have been conducted on planktonic and benthic foraminifera from the western north atlantic to reconstruct sea surface temperatures ssts and deep water temperatures and the structure of the water column around this major biotic turnover whilst the extinctions of m spinulosa and a praetopilensis occur during a long term cooling trend the biotic turnover in the muricate group does not appear to be related to significant climatic change sea surface temperatures decrease slowly prior to the extinction events and there is no evidence for a large temperature shift associated with the faunal changes the turnover event was therefore probably related to the increased surface water productivity and the deterioration of photosymbiotic partnerships with algae d 2003 elsevier b v all rights reserved

intratest oxygen isotope variability in the planktonic foraminifer n pachyderma real vs apparent vital effects by ion microprobe abstract intratest oxygen isotope variations in the planktonic foraminifer neogloboquadrina pachyderma sinistral left coiling from north atlantic core top and multi net samples were assessed by ion microprobe analysis from 2 to 6 m spots with precision and accuracy better than 0 7 in 18 o 2 sd within a single foraminiferal test from a core top sample comprising both ontogenetic calcite and outer crust 18 o values vary from 0 5 to 3 7 pdb exceeding the range of equilibrium 18 o in the specimens habitat by a factor of three the isotopic difference between the ontogenetic calcite and the crust averages 1 8 neither of the two types of foraminiferal calcite precipitates in equilibrium with ambient seawater the ontogenetic calcite exhibits a negative vital effect 18 o m e 18 o measured 18 o equilibrium ranging from 0 5 to 1 the largest negative fractionation is associated to the inner walls of juvenile chambers in contrast a positive vital effect of about 0 8 was observed in the crust with respect to the highest equilibrium 18 o values at water depths below 200 m hence two vital effects that are opposite in sign are effective within a single foraminiferal test indicating that whole test values of this species are highly sensitive to the degree of encrustation and amplify or attenuate environmental signals the negative vital effect of the ontogenetic calcite was verified by ion microprobe analysis of four nonencrusted net sampled specimens reflecting three different depth intervals intra ontogenetic oxygen isotope ratios in these juvenile tests range from 0 6 to 3 0 and exhibit a negative vital effect even larger than that observed in core top samples based on these data the large range of apparent vital effects reported for this foraminiferal species can be assessed by a mass balance calculation assuming that the degree of encrustation is variable

novel observations on biomineralization processes in foraminifera and implications for mg ca ratio in the shells stable isotopes and trace elements in foraminifera shells are important for determining the paleochemistry of the ocean and mg ca ratios and 1 8 o values in foraminifera have recently been used to determine simultaneously the temperature and salinity of past oceans however large variations between species and significant mg intra shell heterogeneity indicate a major role for biological factors in determining the mg ca ratio in foraminifera our novel in vivo observations on the biomineralization process of perforate foraminifera show that their calcareous wall is composed of two different calcite types a thin high mg primary layer and low mg layers that cover the primary layer on both sides the data may suggest that two biomineralization pathways are employed in the formation of the different calcite types a new conceptual framework is provided to explain part of the mg heterogeneity in foraminiferal shells and the variable sensitivity of the mg ca ratio to temperature in different species

microstructural and geochemical perspectives on planktic foraminiferal preservation glassy versus frosty in recent years it has become apparent that the cool tropic paradox of paleogene and cretaceous greenhouse climates arises because of the diagenetic alteration of tropical planktic foraminiferal calcite near the seafloor yielding artificially high 18o values because the mg ca compositions of foraminiferal and inorganic calcite are thought to be quite different mg ca measurements should be a sensitive way of monitoring diagenetic alteration here we examine the extent of diagenetic alteration of eocene planktic foraminiferal calcite using scanning electron microscope imaging of foraminiferal test microstructures and geochemical 18o and mg ca analyses we compare microstructural and geochemical characteristics between given species exhibiting two contrasting states of preservation those that appear frosty under reflected light and those that appear glassy microstructural evidence reveals extensive diagenetic alteration of frosty foraminiferal tests at the micron scale while 18o analyses document consistently higher 18o and therefore lower paleotemperatures in this material yet we find that 18o offsets between species in these frosty foraminiferal assemblages appear to be generally preserved suggesting that frosty foraminifera remain valuable for generating relatively short approximately 1 myr paleoceanographic time series that do not demand absolute estimates of paleotemperature we also find that the observed increase in mg ca for planktic foraminifera exhibiting diagenetic alteration compared to glassy taphonomies is far smaller than would be expected from the addition of inorganic calcite based on laboratory derived mg2 partition coefficients our findings imply that a much lower mg2 partition coefficient controls inorganic calcite formation in deep sea sedimentary sections in accordance with the findings of baker et al 1982

stable warm tropical climate through the eocene epoch earth s climate cooled from a period of extreme warmth in the early eocene epoch ca 50 ma to the early oligocene ca 33 ma when a large ice cap first appeared on antarctica evidence from the planktonic foraminifer oxygen isotope record in deep sea cores has suggested that tropical sea surface temperatures declined by 5 10 degrees over this interval eventually becoming much cooler than modern temperatures here we present paleotemperature estimates from foraminifer isotopes and the membrane lipids of marine crenarcheota from new drill cores in tanzania that indicate a warm and generally stable tropical climate over this period we reinterpret the previously published isotope records in the light of comparative textural analysis of the deep sea foraminifer shells which shows that in contrast to the tanzanian material they have been diagenetically recrystallized we suggest that increasingly severe alteration of the deep sea plankton shells through the eocene produced a diagenetic overprint on their oxygen isotope ratios that imparts the false appearance of a tropical sea surface cooling trend this implies that the long term eocene climatic cooling trend occurred mainly at the poles and had little effect at lower latitudes

climatic responses to tropical sea surface temperature changes on a greenhouse earth the uncertainty associated with tropical sea surface temperatures ssts during past greenhouse climates may have important and unaccounted for effects we explore early paleogene climatic sensitivity to changes in tropical subtropical ssts with a general circulation model we demonstrate that tropical sst changes have local and far field climatic effects underscoring their importance in understanding greenhouse climates the responses of winds upwelling and surface water balance to tropical sst changes are substantial our results indicate that current tropical sst reconstructions may have a significant cool bias despite corrections and that the existence of hot 30 c tropical ssts may be realistic for greenhouse climate intervals including the eocene

oxygen isotope exchange in a two layer model of oceanic crust abstract a numerical model is presented for the transport and exchange of oxygen isotopes in an idealized two layer oceanic crust basalt carbonate that is saturated with a non advecting pore fluid open to the overlying ocean the model allows for time varying sedimentation rate porosity chemical diffusivity and temperature dependent 18o fractionation factors reaction is modeled as solution precipitation of calcite in the carbonate sediment and as modified solution precipitation basalt dissolves smectite precipitates in the basalt layer generic models using input parameters that are typical of those measured in dsdp odp cores and constant sedimentation rates illustrate the behavior of the system sufficiently well to allow first order effects to be discerned that have important implications for paleotemperature and ocean floor weathering studies the solution precipitation reactions allow oxygen to be exchanged between the low 18o basalt layer and the high 18o carbonate sediment through the medium of the pore fluids this results in 18o increasing upwards in the basalt and decreasing downwards in the sediment pore fluid 18o values decrease with depth from zero to values of 1 to 3 at the basalt sediment interface and to values of 7 to 15 within the basalt because reaction rates are slow relative to diffusion in the pore fluid high frequency 18o variations in the solid are preserved indefinitely but the amplitude of the variations decreases as e rt where r is the reaction rate fraction reacted per unit time the results suggest that the diagenetic shifts of the 18o values of benthic and high latitude planktonic foraminifera samples younger than oligocene age are typically negligible for samples older than 50 ma diagenetic effects are typically significant and generally cause estimates of bottom and high latitude surface ocean temperatures in the cretaceous and early tertiary to be too high on the other hand the model suggests that diagenesis will shift the 18o values of low latitude planktonic foraminifera to higher values and that paleotemperature estimates of low latitude surface waters particularly in the eocene and oligocene may be too low using a synthetic 18o record for dsdp site 167 we demonstrate how numerical models can be used to correct specific measured records for diagenesis this approach could provide a means of extracting paleotemperature information from heavily altered late cretaceous and older samples and for quantifying the subtle effects of diagenesis on the 18o record at all sites

evolutionary consequences of the latest paleocene thermal maximum for tropical planktonic foraminifera study of planktonic foraminiferal assemblages preserved in the central equatorial pacific odp site 865 reveal that genera which inhabited the near surface mixed layer diversified during the latest paleocene thermal maximum lptm this transient diversification gave rise to a suite of short lived 50 to several 100 ka distinctive morphotypes morozovella allisonensis sp nov m africana and acarinina sibaiyaensis that are restricted to the lptm interval parallel morphometric and stable isotopic data have been recorded from individual shells of members of the m velascoensis m allisonensis and a soldadoensis a sibaiyaensis lineages the single specimen isotope data confirm that m allisonensis and a sibaiyaensis are indeed stratigraphically restricted to the lptm carbon isotope excursion all specimens recorded anomalously low 13c values a stratigraphic succession of single specimen isotope data from within the 13c excursion interval was used to reconstruct the complex population dynamics which mediated the rapid 10 ka evolution of the lptm taxa these data reveal that local populations of ancestral m velascoensis temporarily collapsed with the descendant m allisonensis suddenly originating from a peripherally isolated population this pattern is most consistent with peripatric speciation overall the evolutionary transition from acarinina soldadoensis to a sibaiyaensis is most consistent with sympatric speciation although certain elements of this transition are suggestive of a parapatric mechanism we postulate that the rapid evolution of the lptm taxa a sibaiyaensis and m allisonensis was fostered by a deepening of the nutrient depleted mixed layer alternatively the lptm morphotypes m allisonensis and a sibaiyaensis may have been extreme ecophenotypic variants arrayed along an intensified ecological gradient support for this latter interpretation is derived from the morphometric data which clearly show the morphological intergradation of the lptm taxa with their respective ancestors thus the morphologic diversification seen during the lptm may represent failed speciations both scenarios invoke a temporary steepening of clinal gradients in response to intensified oligotrophy the strong size dependencies displayed by the 18o and 13c signatures of m allisonensis and a sibaiyaensis suggest that photosymbiosis facilitated the evolutionary success of the morozovellids and acarininids during the lptm

testing the cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the turonian tropics on demerara rise glassy turonian foraminifera preserved in clay rich sediments from the western tropical atlantic yield the warmest equivalent 18o sea surface temperatures ssts yet reported for the entire cretaceous cenozoic we estimate turonian ssts that were at least as warm as conservative mean 30 c to significantly warmer warm mean 33 c than those in the region today however if independent evidence for high middle cretaceous pco2 is reliable and resulted in greater isotopic fractionation between seawater and calcite because of lower sea surface ph our conservative and warm sst estimates would be even higher 32 and 36 c respectively our new tropical ssts help reconcile geologic data with the predictions of general circulation models that incorporate high cretaceous pco2 and lend support to the hypothesis of a cretaceous greenhouse our data also strengthen the case for a turonian age for the cretaceous thermal maximum and highlight a 20 40 m y mismatch between peak cretaceous cenozoic global warmth and peak inferred tectonic co2 production we infer that this mismatch is either an artifact of a hidden turonian pulse in global ocean crust cycling or real evidence of the influence of some other factor on atmospheric co2 and or ssts a hidden pulse in crust cycling would explain the timing of peak cretaceous cenozoic sea level also turonian but other factors are needed to explain high frequency 10 100 k y instability in middle cretaceous ssts reported elsewhere

warming the fuel for the fire evidence for the thermal dissociation of methane hydrate during the paleocene eocene thermal maximum dramatic warming and upheaval of the carbon system at the end of the paleocene epoch have been linked to massive dissociation of sedimentary methane hydrate however testing the paleocene eocene thermal maximum hydrate dissociation hypothesis has been hindered by the inability of available proxy records to resolve the initial sequence of events the cause of the paleocene eocene thermal maximum carbon isotope excursion remains speculative primarily due to uncertainties in the timing and duration of the paleocene eocene thermal maximum we present new high resolution stable isotope records based on analyses of single planktonic and benthic foraminiferal shells from ocean drilling program site 690 weddell sea southern ocean demonstrating that the initial carbon isotope excursion was geologically instantaneous and was preceded by a brief period of gradual surface water warming both of these findings support the thermal dissociation of methane hydrate as the cause of the paleocene eocene thermal maximum carbon isotope excursion furthermore the data reveal that the methane derived carbon was mixed from the surface ocean downward suggesting that a significant fraction of the initial dissociated hydrate methane reached the atmosphere prior to oxidation

the alpine nappe stack in western austria a crustal scale cross section based on an n s oriented crustal scale cross section running east of the rhine valley in vorarlberg western austria we address the alpine nappe stack and discuss the boundary between central and eastern alps for our cross section we used surface geology drillings and reinterpreted seismic lines together with published sections the general architecture of the examined area can be described as a typical foreland fold and thrust belt comprising the tectonic units of the subalpine molasse ultra helvetic penninic and austroalpine nappes these units overthrusted the autochthonous molasse along the south dipping listric alpine basal thrust the european basement together with its autochthonous cover dips gently towards the south and is dissected by normal faults and trough structures the seismic data clearly show an offset not only of the top of the european basement but also of the mesozoic cover and the lower marine molasse this indicates an activity of the structures as normal faults after the sedimentation of the lower marine molasse the subalpine molasse is multiply stacked forming a triangle zone at the boundary with the foreland molasse the shortening within the subalpine molasse amounts to approximately 45 km 67 as deduced from our cross section with the lower marine molasse as a reference the hinterland dipping duplex structure of the helvetic nappes is deduced from surface and borehole data there are at least two helvetic nappes needed to fill the available space between the molasse below and the northpenninic above this is in line with the westerly located nrp20 east transect schmid et al tectonics 15 5 1047 1048 1996 schmid et al the transmed atlas the mediterranean region from crust to mantle 2004 where the two helvetic nappes are separated by the santis thrust yet in contrast to the helvetic nappes in the nrp20 east transect both of our helvetic nappes comprise cretaceous and jurassic strata this change is explained by an eastward down stepping of the santis thrust along a pre existing approximately n s striking lateral ramp bounding an inverted jurassic graben structure below the rhine valley this causes the santis thrust to detach the base cretaceous west of the rhine valley and the base jurassic units east of it this graben controlled change in detachment level leads to the formation of quite different nappe stacks on either side of the rhine valley and a fault controlled appearance of the boundary between the central and eastern alps

late paleocene to eocene paleoceanography of the equatorial pacific ocean stable isotopes recorded at ocean drilling program site 865 allison guyot an expanded and largely complete upper paleocene to upper eocene section was recovered from the pelagic cap overlying allison guyot mid pacific mountains at ocean drilling program odp site 865 18o26 n 179o33 w paleodepth 1300 1500 m reconstructions show that the site was within a few degrees of the equator during the paleogene because no other paleogene sections have been recovered in the pacific ocean at such a low latitude site 865 provides a unique record of equatorial pacific paleoceanography detailed stable isotopic investigations were conducted on three planktonic foraminiferal taxa species of acarinina morozovella and subbotina we studied benthic foraminiferal isotopes at much lower resolution on species of cibicidoides and lenticulina nuttallides truernpyi and gavelinella beccariiformis because of their exceptional rarity the 5180 and 513c stratigraphies from site 865 are generally similar to those derived from other paleocene and eocene sections the planktonic foraminiferal records at site 865 however include significantly less short term single sample variability than those from higher latitude sites indicating that this tropical oligotrophic location had a comparatively stable water column structure with a deep mixed layer and less seasonal variability low amplitude 0 1 0 8 o oscillations on timescales of 250 000 to 300 000 years correlate between the 513c records of all planktonic taxa and may represent fluctuations in the mixing intensity of surface waters peak sea surface temperatures of 24o 25oc occurred in the earliest eocene followed by a rapid cooling of 3 6oc in the late early eocene temperatures remained cool and stable through the middle eocene in the late eocene surface water temperatures decreased further vertical temperature gradients decreased dramatically in the late paleocene and were relatively constant through much of the eocene but increased markedly in the late eocene intermediate waters warmed through the late paleocene reaching a maximum temperature of 10oc in the early eocene cooling in the middle and late eocene paralleled that of surface waters with latest eocene temperatures below 5oc extinction patterns of benthic foraminifera in the latest paleocene were similar to those observed at other pacific sites and were coeval with a short term very rapid negative excursion in 513c values in planktonic and benthic taxa as at other sites during this excursion benthic foraminiferal 5180 values decreased markedly indicating warming of 4 to 6oc for tropical intermediate waters while planktonic taxa show slight warming 1 oc followed by 2oc of cooling convergence of 5180 values of planktonic and benthic foraminifera suggests that thermal gradients in the water column in this tropical location collapsed during the excursion these data are consistent with the hypothesis that equatorial pacific surface waters were a potential source of warm higher salinity waters which filled portions of the deep ocean in the latest paleocene oxygen isotopic data indicate that equator to high southern latitude sea surface thermal gradients decreased to as little as 4oc at the peak of the excursion suggesting some fundamental change in global heat transport

paired δ18o signals of neogloboquadrina pachyderma s and turborotalita quinqueloba show thermal stratification structure in nordic seas abstract the vertical density gradients in the nordic seas are crucial for the preconditioning of the surface water to thermohaline sinking in winter these gradients can be reconstructed from paired oxygen isotope data in tests of different species of planktonic foraminifera the isotopic signatures of which represent different calcification depths in the water column comparison of 18 o values from foraminiferal tests in plankton hauls sediment traps and nearby core top samples with the calculated 18 o calcite profile of the water column revealed species specific 18 o vital effects and the role of bioturbational admixture of subfossil specimens into the surface sediment on the basis of core top samples obtained along a west east transect across various hydrographic regions of the nordic seas 18 o values of turborotalita quinqueloba document apparent calcification depths within the pycnocline at 25 75 m water depth the isotopic signatures of neogloboquadrina pachyderma s reflect water masses near and well below the pycnocline between 70 and 250 m off norway where the atlantic inflow leads to thermal stratification here temperatures in the calcification depth of n pachyderma s differ from sea surface temperature by approximately 2 5 c in contrast n pachyderma s calcifies very close to the sea surface 20 50 m in the arctic domain of the western nordic seas however further west n pachyderma s prefers somewhat deeper more saline water at 70 130 m well below the halocline that confines the low saline east greenland current this implies that the 18 o values of n pachyderma s do not fully reflect the freshwater proportion in surface water and that any reconstruction of past meltwater plumes based on 18 o is too conservative because it overestimates sea surface salinity minimum 18 o differences n pachyderma s and t quinqueloba may serve as proxy for sea regions with dominant haline and absent thermal stratification whereas thermal stratification leads to 18 o differences of 0 4 to 1 5

direct assessment of stable isotope variability in planktonic foraminifera populations abstract a large number of tests of three species of planktonic foraminifera globigerinoides sacculifer orbulina universa and pulleniatina obliquiloculata were analyzed for stable oxygen and carbon isotopes in a western equatorial pacific box core estimates of population variance were calculated using a statistical technique known as the jackknife these estimates were used to generate sampling curves which provide the number of foraminiferal tests required in an isotopic analysis when precision and reliability criteria are specified the jackknife results have important sampling implications 1 a large number of foraminiferal tests are required to obtain statistically reliable isotope data for example given a machine precision standard deviation of 0 09in0 417 tests g sacculifer 355 420 m are required to obtain a 18 o precision of 0 1in0 with 90 reliability 2 variance is a function of test diameter with greater variance being found in larger size fractions 3 variance is dependent on foraminiferal species 4 variance differences between glacial and interglacial samples are not significant 5 in the size interval 600 900 m a systematic relationship is not seen between size and 18 o or 13 c 6 replicate analysis is a practical method of improving isotope data quality size and species related variance differences are probably related to a number of factors including depth habitat seasonal production of tests species vertical migrations and vital and or symbiosis caused effects knowledge of data variance permits error assessment in sediment unmixing analyses and optimization of spectral estimates

late cretaceous oceans and the cool tropic paradox oxygen isotopic proxies of paleo sea surface temperatures ssts suggest that maastrichtian about 66 million years ago tropical ssts were lower than those of today they also demonstrate that maastrichtian latitudinal sst gradients were much lower than those of the present the low maastrichtian sst gradients indicate that meridional heat transport was much greater or latitudinal differences in the balance of radiation to and from the sea surface were much less extreme during the latest cretaceous than they are today or that both conditions were true these findings challenge traditional interpretations of greenhouse late cretaceous climates

a transient rise in tropical sea surface temperature during the paleocene eocene thermal maximum the paleocene eocene thermal maximum petm has been attributed to a rapid rise in greenhouse gas levels if so warming should have occurred at all latitudes although amplified toward the poles existing records reveal an increase in high latitude sea surface temperatures ssts 8 to 10 c and in bottom water temperatures 4 to 5 c to date however the character of the tropical sst response during this event remains unconstrained here we address this deficiency by using paired oxygen isotope and minor element magnesium calcium ratios of planktonic foraminifera from a tropical pacific core to estimate changes in sst using mixed layer foraminifera we found that the combined proxies imply a 4 to 5 c rise in pacific sst during the petm these results would necessitate a rise in atmospheric pco 2 to levels three to four times as high as those estimated for the late paleocene

impact of biomineralization processes on the mg content of foraminiferal shells a biological perspective the mg ca ratio in foraminiferal shells is widely used as a proxy for paleotemperatures nevertheless it seems that the basic mg content of foraminifera is determined by biological factors as can be concluded from the large inter species and intrashell variability and the frequent deviations from inorganic behavior this paper discusses three possible ways by which foraminifera can control or modify the mg content in their shell 1 involvement of organic matrix in the precipitation process that may alter the partition coefficient of mg in biogenic calcite 2 controlled conversion of transient amorphous phases to calcite and 3 modification of the mg concentration in the parent solution from which the crystals precipitate the first two mechanisms are probably responsible for the precipitation of high mg calcite phases whole shell or sublayers while the third mechanism leads to the formation of low mg calcite phases we propose a model adapted from epithelial cells that allows massive mg2 removal from the biomineralization site this model is especially relevant to the planktonic and deep benthic low mg foraminifera that are frequently used for paleotemperature reconstructions we discuss the possible biological roles of mg in the shell in terms of the calcite polymorph conservation the in vivo chemical stability of the shell the functions of mg as a stabilizer of transient phases and as a controlling agent of the precipitation process several temperature sensitive biological processes that may influence the mg ca ratio of the shell are suggested and a model that combines biogenic and inorganic considerations is presented the model uses mg heterogeneity in the shell together with temperature response biologic and inorganic of biomineralization processes to account for the deviation of planktonic foraminifera from inorganic calcite at equilibrium with seawater

modelling the oxygen isotope distribution of ancient seawater using a coupled ocean atmosphere gcm implications for reconstructing early eocene climate one of the motivations for studying warm climates of the past such as the early eocene is the enhanced understanding this brings of possible future greenhouse conditions traditionally climate information deduced from biological or chemical proxies have been used to test computer model simulations of past climatic conditions and hence establish some of the uncertainties associated with model based predictions however extracting climate information from proxies is itself an interpretative process and discrepancies between climate information inferred from different types of proxy undermines the assumption that model data conflicts automatically mean that the model is inherently flawed a new approach which both acknowledges and reduces the uncertainties associated with both model and data is required although the oxygen isotopic ratio 18o preserved in calcareous marine fossils has been used to reconstruct past seawater temperature for several decades significant uncertainties associated with this method persist these include assumptions about past seawater 18o for which no proxy exists and which is a key control on the temperature inferred from fossil carbonate here we present the results of an early eocene simulation made using a state of the art general circulation model gcm hadcm3 with co2 set at six times pre industrial values and which has oxygen isotopes incorporated into the full hydrological cycle and hence simulates the 18o of past seawater this allows us to explore the implications of the different seawater 18o correction factors commonly used for 18o based temperature reconstruction it also allows us to focus model data comparison on 18o rather than interpret ocean temperature an approach that reduces uncertainties in model data comparison since the effects of both the temperature and the isotopic composition of ocean water on 18o of carbonate are accounted for the good agreement between model and data for both modern and well preserved early eocene carbonate increases confidence in climate reconstructions of this time

reconstructing past sea surface temperatures correcting for diagenesis of bulk marine carbonate abstract a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate is used to obtain information on how sea surface temperatures have varied in the past by correcting measured 18o values of bulk carbonate for diagenetic overprinting comparison of bulk carbonate and planktonic foraminiferal 18o records from odp site 677a indicates that the oxygen isotopic composition of bulk carbonate does reflect changes in sea surface temperature and 18o at odp site 690 we calculate that diagenetic effects are small and that both bulk carbonate and planktonic foraminiferal 18o records accurately reflect paleogene warming of high latitude surface oceans biased from diagenesis by no more than 1 c the same is likely to be true for other high latitude sites where sedimentation rates are low at dsdp sites 516 and 525 the effects of diagenesis are more significant measured 18o values of eocene bulk carbonates are more than 2 lower at deeply buried site 516 than at site 525 consistent with the model prediction that the effects of diagenesis should be proportional to sedimentation rate model corrections reconcile the differences in the data between the two sites the resulting paleotemperature reconstruction indicates a 4 c cooling of mid latitude surface oceans since the eocene at low latitudes the contrast in temperature between the ocean surface and bottom makes the carbonate 180 values particularly sensitive to diagenetic effects most of the observed variations in measured 18o values are accounted for by diagenetic effects rather than by sea surface temperature variations we show that the data are consistent with constant equatorial sea surface temperatures through most of the cenozoic with the possible exception of the early eocene when slightly higher temperatures are indicated we suggest that the lower equatorial sea surface temperatures for the eocene and oligocene reported in other oxygen isotope studies are artifacts of diagenetic recrystallization and that it is impossible to reconstruct accurately equatorial sea surface temperatures without explicitly accounting for diagenetic overprinting

equatorial sea surface temperatures for the maastrichtian revealed through remarkable preservation of metastable carbonate the classic paleotemperature record based on 18 o data from pelagic foraminiferal calcite suggests that equatorial sea surface temperatures during the maastrichtian 12 20 c were much cooler than today 27 29 c such cool equatorial temperatures contradict basic theories of tropical atmospheric and ocean dynamics we report 18 o data from remarkably well preserved rudist aragonite and magnesian calcite cements of maastrichtian age 69 1 ma from the carbonate platform of wodejebato guyot in the western pacific these data suggest that equatorial sea surface temperatures in the maastrichtian best estimate 27 32 c were at least as warm as today this finding helps reconcile the geologic 18 o record with ocean atmospheric dynamic theory and implies a reduction in the poleward heat flux required by global climate simulations of greenhouse conditions

foraminifer test preservation and diagenesis comparison of high latitude eocene sites foraminifer tests are prone to diagenetic recrystallization on a micron scale that can affect their geochemical composition hence it is important to identify fossil material that is well preserved here we illustrate the textures of tests from several high latitude eocene sites using a combination of reflected light microscopy and high resolution scanning electron microscopy the sites are ocean drilling program odp site 647 in the labrador sea 53 n odp site 689 at maud rise in the weddell sea 64 s odp site 1135 kerguelen plateau c 59 s and outcrop samples from hampden beach new zealand palaeolatitude c 55 s the foraminifera studied from site 647 and hampden beach have glassy transparent tests that show only minor signs of diagenetic alteration whereas the foraminifera from sites 690 and 1135 are opaque and recrystallized we associate the better state of foraminifer preservation at the former sites with the high clay content of the sediments our observations suggest that site 647 and hampden beach may be useful for the establishment of high latitude sea surface temperatures and hence global temperature gradients in the eocene

topography of the northern hemisphere of mercury from messenger laser altimetry laser altimetry by the messenger spacecraft has yielded a topographic model of the northern hemisphere of mercury the dynamic range of elevations is considerably smaller than those of mars or the moon the most prominent feature is an extensive lowland at high northern latitudes that hosts the volcanic northern plains within this lowland is a broad topographic rise that experienced uplift after plains emplacement the interior of the 1500 km diameter caloris impact basin has been modified so that part of the basin floor now stands higher than the rim the elevated portion of the floor of caloris appears to be part of a quasi linear rise that extends for approximately half the planetary circumference at mid latitudes collectively these features imply that long wavelength changes to mercury s topography occurred after the earliest phases of the planet s geological history

influence of temperature on the composition of magnesian calcite overgrowths precipitated from seawater a constant disequilibrium technique was used to determine the composition of magnesian calcite overgrowths precipitated on pure calcite seeds from artificial seawater at 5 25 and 40 c the amount of magnesium incorporated in the overgrowths at a given temperature is independent of the precipitation rate over a wide range of saturation states and is believed to correspond to a composition in true equilibrium with seawater the distribution coefficient of magnesium dmg2 c in the magnesian calcite overgrowths increases almost linearly with temperature being 0 0121 0 0013 at 5 c 0 0172 0 0022 at 25 c and 0 0271 0 0013 at 40 c these values apply only to magnesian calcites precipitated from standard composition seawater since a previous study has shown dmg2 c to be a function of the mg2 ca2 ratio in the parent solution results of this study are compared with values reported previously by other workers and with the compositional distribution of naturally occurring magnesian calcite cements and ooids found in seawater it appears that variations in temperature are not sufficient to account for the compositional variability of naturally occurring inorganic marine magnesian calcite cements

the climate of the eocene ocean oxygen isotope palaeotemperature estimates are presented for a number of deep sea sediment samples of eocene age covering a wide geographical area these are plotted on a geographical reconstruction for 50 ma the latitudinal temperature gradient at that time was less than half its present value surface temperature at high latitudes was about 10 c and at low latitudes little over 20 c it is concluded that ocean currents must have contributed a greater proportion of the poleward transport of heat than they do at present

jiggling the tropical thermostat in the cretaceous hothouse modern open ocean sea surface temperatures rarely exceed 28 29 8c and the same has been thought to represent a rough maximum for past tropical climates however new isotopic estimates from the uppermost cenomanian in the tropical western north atlantic suggest that mixed layer temperatures reached 33 34 8 c 62 8c during the middle cretaceous hothouse uppermost cenomanian tropical sea surface temperatures may have been as much as 4 7 8c warmer than the highest modern mean annual temperatures such extreme conditions suggest that warm tropical oceans could have driven substantially intensified atmospheric heat transport near the cenomanian turonian boundary the tropical thermostat was set higher than today challenging the hypothesis of tropical climate stability

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

planktonic foraminiferal oxygen isotope analysis by ion microprobe technique suggests warm tropical sea surface temperatures during the early paleogene 1 cool tropical sea surface temperatures ssts are reported for warm paleogene greenhouse climates based on the 18o of planktonic foraminiferal tests these results are difficult to reconcile with models of greenhouse gas forced climate it has been suggested that this cool tropics paradox arises from postdepositional alteration of foraminiferal calcite yielding erroneously high 18o values recrystallization of foraminiferal tests is cryptic and difficult to quantify and the compilation of robust 18o records from moderately altered material remains challenging scanning electron microscopy of planktonic foraminiferal chamber wall cross sections reveals that the basal area of muricae pustular outgrowths on the chamber walls of species belonging to the genus morozovella contain no mural pores and may be less susceptible to postdepositional alteration we analyzed the 18o in muricae bases of morozovellids from the central pacific ocean drilling program site 865 by ion microprobe using 10 m pits with an analytical reproducibility of 0 34 2 standard deviations in situ measurements of 18o in these domains yield consistently lower values than those published for conventional multispecimen analyses assuming that the original 18o is largely preserved in the basal areas of muricae this new 18o record indicates early paleogene 49 56 ma tropical ssts in the central pacific were 4 8 c higher than inferred from the previously published 18o record and that ssts reached at least 33 c during the paleocene eocene thermal maximum this study demonstrates the utility of ion microprobe analysis for generating more reliable paleoclimate records from moderately altered foraminiferal tests preserved in deep sea sediments

extreme warming of mid latitude coastal ocean during the paleocene eocene thermal maximum inferences from tex86 and isotope data changes in sea surface temperature sst during the paleocene eocene thermal max imum petm have been estimated primarily from oxygen isotope and mg ca records generated from deep sea cores here we present a record of sea surface temperature change across the paleocene eocene boundary for a nearshore shallow marine section located on the eastern margin of north america the sst record as inferred from tex86 data indicates a minimum of 8 c of warming with peak temperatures in excess of 33 c similar ssts are estimated from planktonic foraminifer oxygen isotope records al though the excursion is slightly larger the slight offset in the oxygen isotope record may reflect on seasonally higher runoff and lower salinity

a global compilation of late holocene planktonic foraminiferal δ18o relationship between surface water temperature and δ18o we review the different sources of uncertainty affecting the oxygen isotopic composition of planktonic foraminifera and present a global planktonic foraminifera oxygen isotope data set that has been assembled within the margo project for the late holocene time slice the data set consists of over 2100 data from recent sediment with thorough age control that have been checked for internal consistency we further examine how the oxygen isotopic composition of fossil foraminifera is related to hydrological conditions based on published results on living foraminifera from plankton tows and cultures oxygen isotopic values 18o of margo recent fossil foraminifera are 0 2 0 8 higher than those of living foraminifera our results show that this discrepancy is related to the stratification of the upper water mass and generally increases at low latitudes therefore as stratification of surface waters and seasonality depends on climatic conditions the relationship between temperature and 18o established on fossil foraminifera from recent sediment must be used with caution in paleoceanographic studies before models predicting seasonal flux abundance and 18o composition of a foraminiferal population in the sediment are available we recommend studying relative changes in isotopic composition of fossil planktonic foraminifera these changes primarily record variations in temperature and oxygen isotopic composition of sea water although part of the changes might reflect modifications of planktonic foraminifera seasonality or depth habitat

heat transport deep waters and thermal gradients coupled simulation of an eocene greenhouse climate for the first time a coupled general circulation model with interactive and dynamical atmospheric oceanic and sea ice components is used to simulate an eocene 50 ma greenhouse climate we introduce efficient ocean spin up methods for coupled paleoclimate modeling sea surface temperatures ssts and salinities evolve unconstrained producing the first proxy data independent estimates for these eocene climate parameters tropical and extratropical model predicted ssts are warmer than modern values by 3 and 5 c respectively salinity driven deep water formation occurs in the north atlantic and tethys the zonal average overturning circulation is weaker than modern eocene ocean heat transport is 0 6 pw less than modern in the northern hemisphere and 0 4 pw greater in the southern hemisphere the model predicted near modern vertical and meridional eocene temperature gradients imply that the dominant theory for maintaining low gradients increased ocean heat transport is incorrect or incomplete and other mechanisms should be explored

climate deterioration in the eastern mediterranean as revealed by ion microprobe analysis of a speleothem that grew from 2 2 to 0 9 ka in soreq cave israel abstract analysis of oxygen isotope ratios 18 o by ion microprobe resolves a sub annual climate record for the eastern mediterranean from a soreq cave stalagmite that grew between 2 2 and 0 9 ka in contrast to conventional drill sampling methods that yield a total variation of 1 0 in 18 o calcite values across our sample the methods described here reveal up to 2 15 variation within single annual growth bands values of 18 o measured by ion microprobe vary in a regular saw tooth pattern that correlates with annual fluorescent growth banding where calcite grades from light to dark fluorescence modern records of precipitation and of cave dripwater indicate that variable 18 o calcite values record regular seasonal differences in 18 o rainfall modified by mixing in the vadose zone large differences in 18 o values measured across a single band i e between the dark and light fluorescent calcite or 18 o dark light are interpreted to indicate wetter years while smaller differences represent drier years oxygen isotopes record 1 month scale growth increments 2 changes in 18 o dark light that represent seasonality 3 a systematic long term decrease in maximum 18 o dark light values and 4 an overall increase in average 18 o calcite values through time these results suggest a drying of regional climate that coincides with the decline of the roman and byzantine empires in the levant region

eocene equator to pole surface ocean temperatures a significant climate problem eocene surface ocean paleotemperature data which illustrate a reduced equator to pole temperature gradient cooler tropical sea surface temperatures and a relatively small global temperature warming 2 c present a significant climatic enigma if the reconstructions are correct such a temperature distribution can be achieved through greater poleward heat transport by the ocean however the mechanism for a greater oceanic role is uncertain in addition the results from climate models for conditions of a substantially greater poleward heat transport by the oceans indicate a weak atmospheric circulation and highly seasonal continental interior climates the weak atmospheric circulation is consistent with the record of continent derived eolian sediment recovered in deep sea cores however the eocene paleobotanical evidence from continental interiors indicates a very mild seasonality the lack of consistency between model results oceanic data and terrestrial data defines the nature of the problem of eocene climates the solution must involve reinterpretation of at least one major source of information