antarctic climate at the eocene oligocene boundary climate model sensitivity to high latitude vegetation type and comparisons with the palaeobotanical record abstract simulated climate for the antarctic continent using the genesis version 2 1 global climate model with 34 ma boundary conditions is shown to be highly sensitive to polar vegetation type six experiments were run using different levels of atmospheric co2 orbital configurations ice sheet geometries and vegetation types to assess model sensitivity to antarctica being covered with either a needle leaf evergreen forest or tundra simulations using 2 pre industrial levels of co2 combined mean annual temperature mat 19 c are about 7 c cooler than minimum estimates from the antarctic cenozoic plant record mat 12 to 15 c however simulations using 3 co2 mat 7 c are in good agreement with our empirical estimates of mean annual temperature with ice sheets and orbits set up to represent early oligocene interglacial conditions the tundra climate is significantly cooler than the evergreen forest climate with local austral summer averages up to 6 c cooler in non glaciated areas and continental averages 2 5 c cooler in the model this is mainly due to higher albedo and decreases in net radiation and sensible and latent heat flux especially during spring and summer feedbacks between coastal and continental cooling marginal sea surface temperatures and sea ice also appear to be significant a review of the late palaeocene to earliest miocene plant fossil record in the antarctic peninsula and ross sea regions shows that the vegetation was in transition 34 ma from a relatively diverse mainly evergreen forest to a tundra vegetation the modelled sensitivity of continental temperatures to a change from forest to tundra suggests vegetation climate feedbacks during the eocene oligocene transition played a significant role in the initial rapid glaciation of the continent

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

cenozoic ice rafting history of the central arctic ocean terrigenous sands on the lomonosov ridge the cenozoic ice rafted debris ird history of the central arctic is reconstructed utilizing the terrigenous coarse sand fraction in iodp 302 cores from 0 to 273 meters composite depth this holocene middle eocene quantitative record of terrigenous sand accumulation on the lomonosov ridge along with qualitative information on grain texture and composition confirms the interpretation that ice initiation sea ice and glacial ice occurred 46 ma in the arctic and provides a long term pattern of arctic ice expansion and decay since the middle eocene ird mass accumulation rates range from 0 to 0 13 g cm2 ka in the middle eocene and from 0 to 0 36 g cm2 ka in the neogene ird mass accumulation rate mar maxima in the miocene and pliocene cooccur with either glacial initiation or intensification in the sub arctic the 46 25 ma ird onset in the central arctic slightly precedes the earliest evidence of ice in the antarctic and compares in timing with a 1000 ppm decrease in atmospheric concentrations of co2 the decline of pco2 in the middle eocene may have driven both poles across the temperature threshold that enabled the nucleation of glaciers on land and partial freezing of the surface arctic ocean especially during times of low insolation

late eocene to early miocene ice sheet dynamics and the global carbon cycle paired benthic foraminiferal trace metal and stable isotope records have been constructed from equatorial pacific ocean drilling program site 1218 the records include the two largest abrupt 1 myr increases in the cenozoic benthic oxygen isotope record oi 1 in the earliest oligocene 34 ma and mi 1 in the earliest miocene 23 ma the paired mg ca and oxygen isotope records are used to calculate seawater 18o w calculated w suggests that a large antarctic ice sheet formed during oi 1 and subsequently fluctuated throughout the oligocene on both short 0 5 myr and long 2 3 myr timescales between about 50 and 100 of its maximum earliest oligocene size the magnitudes of these fluctuations are consistent with estimates of sea level derived from sequence stratigraphy the transient expansion of the antarctic ice sheet at mi 1 is marked in the benthic 18o record by two positive excursions between 23 7 and 22 9 ma each with a duration of 200 300 kyr bottom water temperatures decreased by 2 c over the 150 kyr immediately prior to both rapid 18o excursions however the onset of each of these phases of ice growth is synchronous within the resolution of the records with the onset of a 2 c warming over 150 kyr we suggest that the warming during these glacial expansions reflect increased greenhouse forcing prompted by a sudden decrease in global chemical weathering rates as antarctic basement silicate rocks became blanketed by an ice sheet this represents a negative feedback process that might have operated during major abrupt growth phases of the antarctic ice sheet

a new perspective on gravity waves in the martian atmosphere sources and features 1 using a mars general circulation model gcm we investigate the characteristics of gravity waves in the atmosphere of mars fluctuations due to internal gravity waves at tidal periods such as diurnal semidiurnal and terdiurnal tides are predominant in the lower atmosphere in particular the diurnal and semidiurnal tides having large zonal wave numbers s 10 are significant fluctuations associated with nontidal gravity wave components in the lower atmosphere are negligibly small except for the stationary orographic component nontidal gravity waves grow in amplitude in the middle atmosphere while tidal components remain the dominant form of gravity waves in the upper atmosphere 80 km nontidal gravity wave components and fluctuations due to the diurnal and semidiurnal tides having large zonal wave numbers are equally important we estimate the global distributions of the gravity wave energy at various altitudes and attempt to define various sources our results show that most nontidal gravity wave energy is closely related with the diurnal amplitude except in the lower atmosphere where association with orography predominates this suggests that nonorographic gravity waves are generated by the breaking and dissipation of the diurnal tide on the other hand nontidal gravity wave energy in the lower atmosphere peaks in mountainous regions and points to their source as being of orographic nature we also enumerate the major differences between gravity waves on mars and earth as simulated by global models

atmospheric pco2 since 60 ma from records of seawater ph calcium and primary carbonate mineralogy a 60 m y record of atmospheric p co2 has been refined from knowledge of 1 secular changes in the major ion composition of seawater particularly ca and mg and 2 oscillations in the mineralogy of primary oceanic carbonate sediments both factors have had a significant impact on the chemistry of the ocean carbonate buffer system calculated atmospheric p co2 oscillated between values of 100 300 ppm and to maxima of 1200 2500 ppm from 60 to 40 ma and varied between 100 and 300 ppm from 25 ma to the present the refined p co2 values are significantly lower than previous estimates made from seawater ph data where total dissolved inorganic carbon was assumed constant and more in line with modeling and stomatal index estimations of atmospheric p co2 for the tertiary

reconstructing past seawater mg ca and sr ca from mid ocean ridge flank calcium carbonate veins proxies for past seawater chemistry such as mg ca and sr ca ratios provide a record of the dynamic exchanges of elements between the solid earth the atmosphere and the hydrosphere and the evolving influence of life we estimated past oceanic mg ca and sr ca ratios from suites of 1 6 to 170 million year old calcium carbonate veins that had precipitated from seawater derived fluids in ocean ridge flank basalts our data indicate that before the neogene oceanic mg ca and sr ca ratios were lower than in the modern ocean decreased ocean spreading since the cretaceous and the resulting slow reduction in ocean crustal hydrothermal exchange throughout the early tertiary may explain the recent rise in these ratios

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

resolving a late oligocene conundrum deep sea warming and antarctic glaciation abstract changes in ice volume and resulting changes in sea level were determined for the late oligocene 26 23 ma astronomical timescale ats by applying 18 o to sea level calibrations to deep sea 18 o records from odp sites 689 690 929 1090 and 1218 our results show that maximum global ice volume occurred during two late oligocene 18 o events oi2c 24 4 ma and mi1 23 0 ma inferred glacioeustatic lowering with volumes up to 25 greater than the present day east antarctic ice sheet eais ice volume during glacial minima was on the order of about 50 of the present day eais this is supported by late oligocene stratigraphic records from antarctica that contain evidence of cold climates and repeated episodes of glaciation at sea level and grounding lines of glacial ice on the antarctic continental shelf in the ross sea and prydz bay in contrast composite deep sea 18 o records show a significant decrease 1 between 26 7 and 23 5 ma which have long been interpreted as bottom water warming combined with deglaciation of antarctica however a close examination of individual 18 o records indicates a clear divergence after 26 8 ma between records from southern ocean locations i e ocean drilling program sites 689 690 744 and those of other ocean basins high 18 o values 2 9 3 3 from these southern ocean 18 o records are consistent with an ice sheet on the east antarctic continent equivalent to present day values and cold bottom water temperatures 2 0 c these differences suggest a reduction in deep water produced near the antarctic continent i e proto antarctic bottom water proto aabw which were quickly entrained and mixed with warmer and presumably more saline bottom water originating from lower latitudes expansion of a warmer deep water mass and the weakening of the proto aabw may explain the large intra basinal isotopic gradients that developed among late oligocene benthic 18 o records these conclusions are also supported by ocean modeling suggesting a reduction of deep water formed in the southern ocean strengthening of deep water from the northern hemisphere and decreasing temperatures in high southern latitudes occurred as the drake passage opened to deep water low 18 o values reported from deep sea locations other than the southern ocean are shown to bias estimates of antarctic ice volume calling for a re evaluation of the notion that antarctic ice volume was significantly reduced during the late oligocene

rapid stepwise onset of antarctic glaciation and deeper calcite compensation in the pacific ocean the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth at present this depth is 4 500 m with some variation between and within ocean basins the calcite compensation depth is linked to ocean acidity which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate1 geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the eocene oligocene boundary 34 million years ago 2 when significant permanent ice sheets first appeared on antarctica3 4 5 6 but the relationship between these two events is poorly understood here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical pacific ocean that cover the eocene oligocene boundary we find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40 000 years each synchronous with the stepwise onset of antarctic ice sheet growth the glaciation was initiated after climatic preconditioning7 by an interval when the earth s orbit of the sun favoured cool summers the changes in oxygen isotope composition across the eocene oligocene boundary are too large to be explained by antarctic ice sheet growth alone and must therefore also indicate contemporaneous global cooling and or northern hemisphere glaciation

eocene bipolar glaciation associated with global carbon cycle changes the transition from the extreme global warmth of the early eocene greenhouse climate 55 million years ago to the present glaciated state is one of the most prominent changes in earth s climatic evolution it is widely accepted that large ice sheets first appeared on antarctica 34 million years ago coincident with decreasing atmospheric carbon dioxide concentrations and a deepening of the calcite compensation depth in the world s oceans and that glaciation in the northern hemisphere began much later between 10 and 6 million years ago here we present records of sediment and foraminiferal geochemistry covering the greenhouse icehouse climate transition we report evidence for synchronous deepening and subsequent oscillations in the calcite compensation depth in the tropical pacific and south atlantic oceans from 42 million years ago with a permanent deepening 34 million years ago the most prominent variations in the calcite compensation depth coincide with changes in seawater oxygen isotope ratios of up to 1 5 per mil suggesting a lowering of global sea level through significant storage of ice in both hemispheres by at least 100 to 125 metres variations in benthic carbon isotope ratios of up to 1 4 per mil occurred at the same time indicating large changes in carbon cycling we suggest that the greenhouse icehouse transition was closely coupled to the evolution of atmospheric carbon dioxide and that negative carbon cycle feedbacks may have prevented the permanent establishment of large ice sheets earlier than 34 million years ago between 55 and 34 million years ago earth switched from a warm greenhouse ocean climate system to the icehouse that we now enjoy frustratingly the few oceanographic datasets that exist for this key period are of low resolution tripati et al now present measurements of sediment and foraminiferal geochemistry that provide the first continuous high resolution records for this period the data suggest that northern hemisphere glaciation started 34 million years ago rather than between 10 and 8 million years ago as previously thought

marked decline in atmospheric carbon dioxide concentrations during the paleogene the relation between the partial pressure of atmospheric carbon dioxide pco2 and paleogene climate is poorly resolved we used stable carbon isotopic values of di unsaturated alkenones extracted from deep sea cores to reconstruct pco2 from the middle eocene to the late oligocene approximately 45 to 25 million years ago our results demonstrate that pco2 ranged between 1000 to 1500 parts per million by volume in the middle to late eocene then decreased in several steps during the oligocene and reached modern levels by the latest oligocene the fall in pco2 likely allowed for a critical expansion of ice sheets on antarctica and promoted conditions that forced the onset of terrestrial c4 photosynthesis

recent controversies in predicting post glacial sea level change abstract we compare recent developments in the numerical prediction of post glacial sea level changes and comment on the controversies associated with these developments we conclude that 1 the broad shelf effect discussed by peltier and drummond 2002 in the context of water load modelling at migrating shorelines is incorporated into the sea level algorithms of johnston 1993 and milne et al 1999 and 2 the procedure used by yokoyama et al 2000 to infer an ice equivalent post lgm sea level rise of 130 135 m is technically sound

significant southern ocean warming event in the late middle eocene a prominent middle eocene warming event is identified in southern ocean deep sea cores indicating that long term cooling through the middle and late eocene was not monotonic at sites on maud rise and the kerguelen plateau a distinct negative shift in 1 8 o values 1 0 is observed ca 41 5 ma this excursion is interpreted as primarily a temperature signal with a transient warming of 4 c over 600 k y affecting both surface and middle bathyal deep waters in the indian atlantic region of the southern ocean this isotopic event is designated as the middle eocene climatic optimum and is interpreted to represent a significant climatic reversal in the midst of middle to late eocene deep sea cooling the lack of a significant negative carbon isotope excursion as observed during the paleocene eocene thermal maximum and the gradual rate of high latitude warming suggest that this event was not triggered by methane hydrate dissociation rather a transient rise in pco 2 levels is suspected possibly as a result of metamorphic decarbonation in the himalayan orogen or increased ridge arc volcanism during the late middle eocene

no extreme bipolar glaciation during the main eocene calcite compensation shift major ice sheets were permanently established on antarctica approximately 34 million years ago1 2 3 close to the eocene oligocene boundary at the same time as a permanent deepening of the calcite compensation depth in the world s oceans4 until recently it was thought that northern hemisphere glaciation began much later between 11 and 5 million years ago1 2 3 5 this view has been challenged however by records of ice rafting at high northern latitudes during the eocene epoch6 7 and by estimates of global ice volume that exceed the storage capacity of antarctica8 at the same time as a temporary deepening of the calcite compensation depth 41 6 million years ago9 here we test the hypothesis that large ice sheets were present in both hemispheres 41 6 million years ago using marine sediment records of oxygen and carbon isotope values and of calcium carbonate content from the equatorial atlantic ocean these records allow at most an ice budget that can easily be accommodated on antarctica indicating that large ice sheets were not present in the northern hemisphere the records also reveal a brief interval shortly before the temporary deepening of the calcite compensation depth during which the calcite compensation depth shoaled ocean temperatures increased and carbon isotope values decreased in the equatorial atlantic the nature of these changes around 41 6 million years ago implies common links in terms of carbon cycling with events at the eocene oligocene boundary4 and with the hyperthermals of the early eocene climate optimum3 10 11 our findings help to resolve the apparent discrepancy between the geological records of northern hemisphere glaciation6 7 8 and model results12 13 that indicate that the threshold for continental glaciation was crossed earlier in the southern hemisphere than in the northern hemisphere

constraints on glaciation in the middle eocene 46 37 ma from ocean drilling program odp site 1209 in the tropical pacific ocean the presence of glacial ice in the late middle eocene has been vigorously debated recently published sedimentary data from the high latitudes is suggestive of episodic cooling events and near freezing sea surface temperatures during parts of the late middle eocene constraints on ice volumes and the significance of excursions in open ocean foraminifera and seawater 18o reconstructions are less clear and there are few high resolution 18o records we present a new detailed record of benthic foraminiferal 18o from site 1209 that exhibits variations 18o benthic of 0 6 1 3 different approaches have previously been used to interpret 18o benthic including 1 an a priori assumption of a 50 contribution of temperature similar to what is reconstructed for the last glacial maximum recent change 2 applying oligocene calibrations between apparent sea level asl and 18o benthic or 3 assuming temperature and seawater 18o contributions can be partitioned through comparison with benthic mg ca using assumption 1 the record from site 1209 indicates changes in seawater 18o of 0 3 0 7 equivalent to 33 72 m m of asl assuming mean ice 18o of 45 using assumption 2 and two different end member calibrations the 18o benthic record implies changes in asl of 23 50 m or 50 108 m the third approach yields changes in seawater 18o of up to 0 6 to 1 4 we explore the compatibility of the results of each of these approaches with other studies that discuss evidence for ephemeral glaciations during the middle eocene with variable ice storage at one or both poles

paleogene calcite compensation depth in the eastern subtropical pacific answers and questions 1 ocean drilling program leg 199 drilled a north south transect across the eocene paleoequator in the eastern pacific permitting reconstruction the calcite compensation depth ccd since earliest eocene time the ccd was relatively shallow near the early eocene pacific equator 3200 m and unlike modern latitudinal ccd gradients deepened to the north to 3600 m paleolatitude 10 n at 41 ma the ccd underwent a brief sharp transient deepening of 700 m then remained shallow until the eocene oligocene boundary at the e o boundary the ccd deepened by 1200 m in less than 300 kyr this rapid deepening served to more than double the area of seafloor subject to caco3 deposition sea level fall associated with ice volume buildup and ensuing shelf basin fractionation is unlikely to be the sole cause of the increased deep ocean caco3 burial rather a sudden rapid increase in the amount of ca entering the ocean appears necessary to explain the observations

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

caco3 dissolution in sediments of the ceara rise western equatorial atlantic we have used porewater sampling by in situ techniques including whole core squeezing as well as by shipboard sectioning and whole core squeezing to estimate the rates of sedimentary organic matter oxidation and caco3 dissolution at seven sites on the ceara rise in the western equatorial atlantic ocean porewater no3 profiles at all sites show a pattern indicative of active organic matter oxidation in the upper 15 20 cm of the sediments and in a buried organic rich layer the organic c oxidation rate generally decreases with increasing water depth from a value of 22 mol cm2 y at the shallowest site 3279 m to 14 mol cm2 y at the deepest site 4675 m over this depth range the bottomwaters vary from moderately supersaturated with respect to calcite to strongly undersaturated high resolution alkalinity profiles measured in porewaters collected by in situ whole core squeezing yield estimated ca2 fluxes of 11 mol cm2 y at a site located at the depth of the calcite saturation horizon and 7 6 zmol cm2 y at a moderately undersaturated site ca2 fluxes calculated from profiles in porewaters collected by relatively coarse resolution in situ sampling methods clearly indicate that there is caco3 dissolution above the calcite saturation horizon the dissolution of aragonite may contribute to the dissolution flux at the shallowest site these ca2 fluxes as well as fluxes estimated from a model of sedimentary organic matter oxidation and calcite dissolution indicate that 36 66 of the caco3 rain to the seafloor dissolves at sites at and above the calcite saturation horizon while 52 75 of the rain dissolves at sites below this depth when these results are incorporated into the oceanic caco3 budget of milliman 1993 they indicate that 35 of caco3 production is preserved in the deep sea they suggest a caco3 accumulation rate that is 27 lower than that estimated by milliman 1993 our corg oxidation caco3 dissolution model indicates that a large fraction of the caco3 dissolution that is occurring on the ceara rise is attributable to the neutralization of metabolic acids produced during organic matter oxidation the efficiency with which organic matter oxidation dissolves caco3 that is the ratio caco3 dissolution attributable to organic matter oxidation organic matter oxidation rate generally increases as degree of undersaturation of bottomwaters increases however there are deviations from the general trend that can be attributed to site to site variations in the kinetics of organic matter oxidation and calcite dissolution this result indicates that the dissolution of caco3 as a result of organic matter oxidation in the deep sea may mask the effects of variations in surface water caco3 productivity and bottomwater chemistry on the accumulation rate of caco3 in deep sea sediments

application of benthic foraminiferal mg ca ratios to questions of cenozoic climate change abstract we investigate the evolution of cenozoic climate and ice volume as evidenced by the oxygen isotopic composition of seawater 18osw derived from benthic foraminiferal mg ca ratios to constrain the temperature effect contained in foraminiferal 18o values we have constructed two benthic foraminiferal mg ca records from intermediate water depth sites ocean drilling program sites 757 and 689 from the subtropical indian ocean and the weddell sea respectively together with the previously published composite record of lear et al science 287 2002 269 272 and the neogene record from the southern ocean of billups and schrag paleoceanography 17 2002 10 1029 2000pa000567 we obtain three almost complete representations of the 18osw for the past 52 myr we discuss the sensitivity of early cenozoic mg ca derived paleotemperatures and hence the 18osw to assumptions about seawater mg ca ratios we find that during the middle eocene 49 40 ma modern seawater ratios yield mg ca derived temperatures that are in good agreement with the oxygen isotope paleothermometer assuming ice free conditions intermediate waters cooled during the middle eocene reaching minimum temperatures by 40 ma the corresponding 18osw reconstructions support ice growth on antarctica beginning by at least 40 ma at the eocene oligocene boundary mg ca ratios and hence temperatures from weddell sea site 689 display a well defined maximum we caution against a paleoclimatic significance of this result and put forth that the partitioning coefficient of mg in benthic foraminifera may be sensitive to factors other than temperature throughout the remainder of the cenozoic the temporal variability among 18osw records is similar and similar to longer term trends in the benthic foraminiferal 18o record an exception occurs during the pliocene when 18osw minima in two of the three records suggest reductions in global ice volume that are not apparent in foraminiferal 18o records which provides a new perspective to the ongoing debate about the stability of the antarctic ice sheet maximum 18osw values recorded during the pleistocene at southern ocean site 747 agree well with values derived from the geochemistry of pore waters schrag et al science 272 1996 1930 1932 further highlighting the value of the new mg ca calibrations of martin et al earth planet sci lett 198 2002 193 209 and lear et al geochim cosmochim acta 66 2002 3375 3387 applied in this study we conclude that the application of foraminiferal mg ca ratios allows a refined view of cenozoic ice volume history despite uncertainties related to the geochemical cycling of mg and ca on long time scales

mg ca in the benthic foraminifera cibicidoides wuellerstorfi and cibicidoides mundulus temperature versus carbonate ion saturation magnesium calcium mg ca ratios in two widely used benthic foraminiferal species cibicidoides wuellerstorfi and cibicidoides mundulus cibicidoides kullenbergi picked from global ocean core tops and from six cores in the north atlantic ocean have been measured to investigate mg ca variability cleaning effect and influences from bottom water temperature bwt and deep water carbonate ion saturation co32 replicate measurements of the two species reveal mg ca variability of 0 07 0 07 mmol mol compared with mg ca in samples cleaned by oxidative cleaning mg ca ratios are significantly lowered by 0 10 0 09 mmol mol in samples cleaned by reductive cleaning likely due to preferential leaching during the reductive cleaning step the cleaning influence is large relative to glacial interglacial mg ca changes 0 05 0 31 mmol mol by this study regression of core top data from a wide range of locations show that c wuellerstorfi mg ca is strongly affected by deep water co32 with a sensitivity of 0 009 mmol mol per mol kg when bwt is included in regressions the correlation is slightly more significant with a weak bwt sensitivity on mg ca of between 0 03 0 01 and 0 07 0 02 mmol mol per c because co32 and bwt co vary for most core top samples an alternate method of separating the two effects was made by comparing glacial to interglacial changes in mg ca from a depth transect of north atlantic cores where the bwt and carbonate ion histories since the last glacial period have been well constrained results from this transect suggest that the bwt effect is 0 03 mmol mol per c weaker than inferred from the core top study therefore core top and down core data suggest that c wuellerstorfi mg ca is insensitive to bwt changes the weak bwt effect when compared with natural variability complicates the use of mg ca in this species to reconstruct past bwt taking all measured samples from various environments into account c mundulus mg ca ratios show no correlation with bwt or deep water co32

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

mg ca ratios of the benthic foraminifera oridorsalis umbonatus obtained by laser ablation from core top sediments relationship to bottom water temperature 1 a laser ablation system connected to an inductively coupled plasma mass spectrometer was used to determine mg ca ratios of the benthic foraminifera oridorsalis umbonatus a set of modern core top samples collected along a depth transect on the continental slope off namibia 320 2300 m water depth 2 9 to 10 4 c was used to calibrate the mg ca ratio against bottom water temperature the resulting mg ca bottom water temperature relationship of o umbonatus is described by the exponential equation mg ca 1 528 e0 09 bwt the temperature sensitivity of this equation is similar to previously published calibrations based on cibicidoides species suggesting that the mg ca ratio of o umbonatus is a valuable proxy for thermocline and deep water temperature

thresholds for cenozoic bipolar glaciation the long standing view of earth s cenozoic glacial history calls for the first continental scale glaciation of antarctica in the earliest oligocene epoch 33 6 million years ago1 followed by the onset of northern hemispheric glacial cycles in the late pliocene epoch about 31 million years later2 the pivotal early oligocene event is characterized by a rapid shift of 1 5 parts per thousand in deep sea benthic oxygen isotope values3 oi 1 within a few hundred thousand years4 reflecting a combination of terrestrial ice growth and deep sea cooling the apparent absence of contemporaneous cooling in deep sea mg ca records4 5 6 however has been argued to reflect the growth of more ice than can be accommodated on antarctica this combined with new evidence of continental cooling7 and ice rafted debris8 9 in the northern hemisphere during this period raises the possibility that oi 1 represents a precursory bipolar glaciation here we test this hypothesis using an isotope capable global climate ice sheet model that accommodates both the long term decline of cenozoic atmospheric co2 levels10 11 and the effects of orbital forcing12 we show that the co2 threshold below which glaciation occurs in the northern hemisphere 280 p p m v is much lower than that for antarctica 750 p p m v therefore the growth of ice sheets in the northern hemisphere immediately following antarctic glaciation would have required rapid co2 drawdown within the oi 1 timeframe to levels lower than those estimated by geochemical proxies10 11 and carbon cycle models13 14 instead of bipolar glaciation we find that oi 1 is best explained by antarctic glaciation alone combined with deep sea cooling of up to 4 c and antarctic ice that is less isotopically depleted 30 to 35 than previously suggested15 16 proxy co2 estimates remain above our model s northern hemispheric glaciation threshold of 280 p p m v until 25 myr ago but have been near or below that level ever since10 11 this implies that episodic northern hemispheric ice sheets have been possible some 20 million years earlier than currently assumed although still much later than oi 1 and could explain some of the variability in miocene sea level records

late eocene tropical sea surface temperatures a perspective from panama 1 we have reconstructed mean annual coastal temperatures and seasonality during the eocene priabonian 36 6 40 ma using oxygen isotope profiles of shallow marine aragonitic gastropod shells gatuncillo formation panama these data provide a unique opportunity to document low latitude coastal climates during a preglacial greenhouse period assuming shell oxygen isotope profiles primarily reflect changes in water temperature our results indicate water temperatures in a middle to outer shelf setting 20 50 m depth varied by 6 8 c and mean annual temperatures mat were 26 c these temperatures are in agreement with pollen based surface temperature reconstructions for the late eocene and are consistent with other eocene mollusk based tropical coastal temperature estimates but are at odds with the few eocene foraminiferal based estimates of mean annual tropical sea surface temperatures 17 22 c

an intensity ratio calibration method for the accurate determination of mg ca and sr ca of marine carbonates by icp aes an inductively coupled plasma atomic emission spectroscopy icp aes method for the accurate and precise simultaneous measurement of the mg ca and sr ca content of carbonates was established while a precision of 0 3 1 standard deviation sd is easily obtainable for both mg ca and sr ca analysis a ca matrix effect complicates achieving similar levels of accuracy with conventional calibration procedures an alternative ratio calibration procedure is proposed which overcomes the ca matrix effects and ensures the accuracy of the mg ca and sr ca analysis of marine carbonates to 0 3 almost an order of magnitude better than conventional calibration methods the longer term precision is 0 1 if the batch run average values are corrected for longer term drift the method is suitable for analysis of foraminiferal calcite and coral aragonite and can easily be adjusted for the analysis of other carbonates or microsamples

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

paleogene biomarker records from the central arctic ocean integrated ocean drilling program expedition 302 organic carbon sources anoxia and sea surface temperature 1 during integrated ocean drilling program expedition 302 arctic coring expedition acex a more than 200 m thick sequence of paleogene organic carbon oc rich black shale type sediments was drilled here we present new biomarker data determined in acex sediment samples to decipher processes controlling oc accumulation and their paleoenvironmental significance during periods of paleogene global warmth and proposed increased freshwater discharge in the early cenozoic specific source related biomarkers including n alkanes fatty acids isoprenoids carotenoids hopanes hopenes hopanoic acids aromatic terpenoids and long chain alkenones show a high variability of components derived from marine and terrestrial origin the distribution of hopanoic acid isomers is dominated by compounds with the biological 17 h 21 h configuration indicating a low level of maturity on the basis of the biomarker data the terrestrial oc supply was significantly enriched during the late paleocene and part of the earliest eocene whereas increased aquatic contributions and euxinic conditions of variable intensity were determined for the paleocene eocene thermal maximum and eocene thermal maximum 2 events as well as the middle eocene time interval furthermore samples from the middle eocene are characterized by the occurrence of long chain alkenones high proportions of lycopane and high ratios 0 6 of n c35 lycopane n c31 the occurrence of c37 alkenenones which were first determined toward the end of the azolla freshwater event indicates that the oc becomes more marine in origin during the middle eocene preliminary u37k based sea surface temperature sst values display a long term temperature decrease of about 15 c during the time interval 49 44 5 ma 25 to 10 c coinciding with the global benthic 18o cooling trend after the early eocene climatic optimum at about 46 ma parallel with onset of ice rafted debris sst interpreted as summer temperatures decreased to values 15 c for the late early miocene a sst of 11 15 c was determined most of the middle eocene acex sediments are characterized by a smooth short chain n alkane distribution which may point to natural oil type hydrocarbons from leakage of petroleum reservoirs or erosion of related source rocks and redeposition

a record of bottom water temperature and seawater δ18o for the southern ocean over the past 440 kyr based on mg ca of benthic foraminiferal uvigerina spp the sensitivity to temperature of mg ca ratios in the shallow infaunal benthic foraminifera uvigerina spp has been assessed core top calibrations over 1 20 c show a range in sensitivity of 0 065 0 084 mmol mol c but few data are available spanning the temperature range anticipated in deep sea records over glacial interglacial cycles in contrast to epibenthic foraminiferal species carbonate ion saturation appears not to affect mg ca significantly a method based on estimating the ratio of the temperature sensitivity of foraminiferal mg ca to that of 18ocalcite shows that sensitivity for mg ca at the high end of the observed core top range 0 1 mmol mol c is required for consistency with lgm holocene differences in each property as constrained by independent proxy data this is supported by a mg ca record for uvigerina spp generated for the southern ocean over the past 440 000 years from ocean drilling program site 1123 chatham rise new zealand the record shows variability that correlates with climate oscillations the lgm deep ocean temperature derived from the mg ca record is 1 1 0 3 c transformation to temperature allows estimates to be made of changes in bottom water temperature and seawater 18o and comparison made with literature records analysis reveals a 2 5 kyr lead in the record of temperature over calcite 18o and a longer lead over seawater 18o this is a reflection of larger phase offsets at eccentricity periods phase offsets at tilt and precession are within error zero

late paleocene arctic coastal climate inferred from molluscan stable and radiogenic isotope ratios abstract characterizing polar climates during past warm intervals is important for understanding greenhouse climate dynamics because high latitude surface temperatures and precipitation patterns are extremely sensitive to global climatic conditions model data comparisons of high latitude climates during past warm intervals cretaceous eocene pliocene are currently at odds specifically simulations of past warm climates produce polar regions characterized by sub freezing temperatures and significant seasonality whereas limited fossil proxy data indicate higher mean annual temperatures and low seasonality i e an equable climate we have constructed a data set to infer northern hemisphere polar marine temperatures during the late paleocene seasonal and mean annual temperature and the oxygen isotopic composition of precipitation are reconstructed for an arctic coastal setting during the thanetian 57 58 ma using fossil shell stable isotope profiles we estimate that coastal water temperatures varied between 10 and 15 c during the seasons of growth presumably spring summer and fall these findings support paleontological evidence implying northern hemisphere polar climates were seasonally warm during the late paleocene in addition estuarine fossil oxygen isotope profiles show periodic excursions to low values as low as 19 vpdb which indicate seasonal pulses of isotopically depleted freshwater

progress in paleosalinity overview and presentation of a new approach this paper concerns the use of stable oxygen isotope ratios 18o and stable hydrogen isotope ratios 2h or d to derive paleosalinity first i evaluate the potential and limitations of existing methods based on 18o and d separately next i propose a new theoretical framework for the combined use of 18o and d to constrain the impact of the hydrological cycle on the surface waters and to thus characterize changes in surface water salinity this new method is accompanied by an error propagation exercise to demonstrate its limitations and areas of potential improvement a feasible strategy is outlined for achieving reconstructions of paleosalinity change with an uncertainty of 1 practical salinity unit or less with the newly proposed method especially in regions with high deuterium excess values

west antarctic paleotopography estimated at the eocene oligocene climate transition 1 one generally recognized limitation of models for rapid growth of antarctic ice near the eocene oligocene transition is that they are based on present topography corrected only for removal of modern ice for west antarctica this results in large areas below sea level that would not readily host ice in the recently active west antarctic rift system other factors may have contributed to significant vertical motions since the eocene additional corrections for thermal contraction resulting from tectonic extension and for erosion and sedimentation since 34 ma restore most of west antarctica to above sea level increasing total antarctic land area by 10 20 because ice sheets have convex slopes the potential increase in ice volume is larger than the increase in land area accounting for large changes in west antarctic topography may resolve conflicts between ice models and data by demonstrating the possibility of an early large west antarctic ice sheet

fluidization in dry landslides this paper aims at determining the physical properties affecting the distance travelled by landslides with dry particles and elucidating the mechanism of the properties affecting landslide fluidization the procedure is as follows laboratory landslide experiments were conducted to verify the simulation model which was proposed to represent the movement of landslides further sensitivity analysis for some physical properties affecting the travel distance were conducted using this model the simulation model could identify the coordinates velocity and angular velocity for every particle in three dimensional space and the kinetic energy of particles consumed by inelastic and frictional collision with each other in the model the travel distances of landslides simulated by the model were verified by laboratory experiments statistically where the physical properties for the particles and slope angle were changed then sensitivity analysis for the physical properties were conducted using the model to clarify the effect of the properties on the travel distance it was proven that there were no significant differences between the travel distances represented by the simulation model and those found experimentally using statistical analysis i e the simulation model could represent virtual real landslides from the sensitivity analysis using the simulation model the travel distances were positively correlated to volume or number of particles and negative correlated to the slope angle kinetic friction and rolling friction of particles when the initial potential energies were the same the mass of particles of equal size did not affect the distance travelled as the number of particles increased the simulated travel distances tended to be longer compared with theoretical travel distances calculated using the friction between particles and the slope consequently we could determine the distance of the lumped mass model as being critical between fluidized and non fluidized landslides

carbon and oxygen isotopic disequilibria of recent deep sea benthic foraminifera abstract the carbon and oxygen isotopic compositions of 149 samples of benthic foraminifera from deep sea core tops indicate that none of the nine species studied secrete calcium carbonate in isotopic equilibrium with ambient bottom water uvigerina pyrgo murrhina and oridorsalis tener are the closest to 18o equilibrium with average deviations about 0 4 while planulina wuellerstorfi and p murrhina are the closest to 13c equilibrium with average deviations about 1 p wuellerstorfi shows the most systematic relationship between 13c and bottom water apparent oxygen utilization the intraspecific variabilities in 18o and 13c suggest that estimates of bottom water paleotemperatures can be made to a precision of 0 7 c while estimates of past apparent oxygen utilization aou can be made to 35 mol kg based on intraspecific comparisons of the recent samples with fossils no temporal changes in the degree of either 18o or 13c disequilibrium have been detected for planulina wuellerstorfi uvigerina oridorsalis tener and globocassidulina subglobosa

evolution of atlantic thermohaline circulation early oligocene onset of deep water production in the north atlantic the flow of deep water masses is a key component of heat transport in the modern climate system yet the role of deep ocean heat transport during periods of extreme warmth is poorly understood the present mode of meridional overturning circulation is characterized by deep water formation in both the north atlantic and the southern ocean however a different mode of meridional overturning circulation operated during the extreme greenhouse warmth of the early cenozoic during which time the southern ocean was the dominant region of deep water formation the combination of general global cooling and tectonic evolution of the atlantic basins over the past 55 m y ultimately led to the development of a mode of overturning circulation characterized by both southern ocean and north atlantic deep water sources the change in deep water circulation mode may in turn have affected global climate however unraveling the causes and consequences of this transition requires a better understanding of the timing of the transition new nd isotope data from the southeastern atlantic ocean indicate that the initial transition to a bipolar mode of deep water circulation occurred in the early oligocene ca 33 ma the likely cause of significant deep water production in the north atlantic was tectonic deepening of the sill separating the greenland norwegian sea from the north atlantic

tertiary ice sheet dynamics the snow gun hypothesis we observe strong negative correlation between tertiary low to mid latitude planktonic foraminiferal 18o and the difference between these data and coeval benthic foraminiferal 18o late quaternary data do not show this correlation coupling statistical model 18o comparisons and evidence for antarctic ice and ocean temperature variation we infer that tertiary ice volume recorded by tropical planktonic 18o increased as the deep ocean warmed because the isotopic signatures of deepwater temperature variation and ice volume change were of opposite sign the sum of these signals in tertiary benthic 18o became lost in the noise this renders low correlation between tertiary planktonic and benthic 18o time series compared to late quaternary data we contend that tertiary ice sheet growth was commonly driven by warming of deep water from low to mid latitude marginal seas snow gun hypothesis in contrast late quaternary ice sheets grew as deep water formed at high latitude cooled because tectonic forcing and orbital forcing at low latitude primarily controlled production and temperature variations of this warm saline deep water these influences largely dictated tertiary ice volume fluctuations through the tertiary we infer ice volume fluctuations to be an important component of sea level history on timescales between 103 and 107 years

visions of ice sheets in a greenhouse world abstract backstripped eustatic estimates from new jersey and the russian platform show large 25 m and rapid 18 o record highlights the enigma this was the warmest interval of the past 200 my yet it was bracketed by two inferred eustatic falls of 25 m that were associated with two large 0 75 deep sea 18 o increases 92 93 ma mid turonian and 96 ma mid cenomanian we reconcile records of warm high latitudes with glacioeustasy by proposing that late cretaceous early eocene ice sheets generally reached maximum volumes of 8 12 10 6 km 3 20 30 m glacioeustatic equivalent but did not reach the antarctic coast hence coastal antarctica hence deep water remained relatively warm even though there were significant changes in sea level as the result of glaciation unlike the oligocene and younger icehouse world these ice sheets only existed during short intervals of peak milankovitch insolation leaving antarctica ice free during much of the greenhouse late cretaceous to middle eocene these results highlight the need to re evaluate the paradigm that polar ice sheets did not exist during times of warm high latitude climates

insights from the paleogene tropical pacific foraminiferal stable isotope and elemental results from site 1209 shatsky rise 1 stable isotope and elemental measurements were conducted on foraminifera from a sequence of calcareous pelagic ooze at ocean drilling program site 1209 to document the thermal evolution of the north pacific water column over shatsky rise and to address long standing questions about the nature of oceanic circulation in the early paleogene a major change in seasonality and water column structure in the early eocene marks a change in tropical pacific climate and circulation just prior to the early eocene climatic optimum subsequent long term cooling is interrupted by a transient positive 18o excursion identified in planktonic and benthic foraminifera during the late early eocene that is interpreted as evidence for ephemeral formation of deep water from a low latitude saline source paired analysis of benthic mg ca and 18o was undertaken to assess the relative contribution of temperature and seawater oxygen isotope composition to the benthic 18o record stratigraphic trends of benthic 18o and mg ca decouple during two intervals in the early eocene and early middle eocene although variable seawater 18o is the most likely candidate to explain decoupling of benthic 18o and mg ca it is difficult to argue for substantial change in continental ice volume during a presumably ice free interval of time

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

eocene sea temperatures for the mid latitude southwest pacific from mg ca ratios in planktonic and benthic foraminifera abstract we have used laser ablation inductively coupled plasma mass spectrometry la icp ms to measure elemental mg ca al ca mn ca zn ca sr ca and ba ca ratios of 13 species of variably preserved early to middle eocene planktonic and benthic foraminifera from new zealand the foraminifera were obtained from ashley mudstone mid waipara river south island which was deposited at bathyal depth ca 1000 m on the northern margin of the east facing canterbury basin at a paleo latitude of ca 55 s la icp ms data yield trace element depth profiles through foraminifera test walls that can be used to identify and exclude zones of surficial contamination and infilling material resulting from diagenetic coatings mineralisation and detrital sediment screened mg ca ratios from 5 species of foraminifera are used to calculate sea temperatures from late early to early middle eocene ca 51 to 46 5 ma a time interval that spans the termination of the early eocene climatic optimum eeco during this time sea surface temperatures sst varied from 30 to 24 c and bottom water temperatures bwt from 21 to 14 c comparison of mg ca sea temperatures with published 18o and tex86 temperature data from the same samples hollis et al 2009 shows close correspondence indicating that la icp ms can provide reliable mg ca sea temperatures even where foraminiferal test preservation is variable agreement between the three proxies also implies that mg ca temperature calibrations for modern planktonic and benthic foraminifera can generally be applied to eocene species although some species e g v marshalli show significant calibration differences the mg ca ratio of the eocene ocean is constrained by our data to be 35 50 lower than the modern ocean depending on which tex86 temperature calibration kim et al 2008 liu et al 2009 is used to compare with the mg ca sea temperatures sea temperatures derived from 18o analysis of foraminifera from waipara show amplified variability relative to the mg ca and tex86 proxies this amplified variability is probably a diagenetic effect although it is possible that this eocene 18o record contains an ice volume component the amplification signalling that temperature changes may have been accompanied by growth and collapse of ephemeral polar ice sheets on timescales of ca 0 5 myr

evidence for glaciation in the northern hemisphere back to 44 ma from ice rafted debris in the greenland sea the widely accepted age estimate for the onset of glaciation in the northern hemisphere ranges between 2 and 15 million years ago ma however recent studies indicate the date for glacial onset may be significantly older we report the presence of ice rafted debris ird in 44 to 30 ma sediments from the greenland sea evidence for glaciation in the north atlantic during the middle eocene to early oligocene detailed sedimentological evidence indicates that glaciers extended to sea level in the region allowing icebergs to be produced ird may have been sourced from tidewater glaciers small ice caps and or a continental ice sheet

temperature and carbonate ion effects on mg ca and sr ca ratios in benthic foraminifera aragonitic species hoeglundina elegans received 16 march 2005 revised 20 june 2005 accepted 3 november 2005 published 21 february 2006 1 core top samples from atlantic little bahama banks lbb and pacific hawaii and indonesia depth transects have been analyzed in order to assess the influence of bottom water temperature bwt and aragonite saturation levels on mg ca and sr ca ratios in the aragonitic benthic foraminifer hoeglundina elegans both the mg ca and sr ca ratios in h elegans tests show a general decrease with increasing water depth although at each site the decreasing trends are consistent with the in situ temperature profile mg ca and sr ca ratios in lbb are substantially higher than in indonesia and hawaii at comparable water depths with a greater difference observed with increasing water depth because we find no significant difference between results obtained on live and dead specimens we propose that these differences are due to primary effects on the metal uptake during test formation evaluation of the water column properties at each site suggests that in situ co3 ion concentrations play an important role in determining the h elegans mg ca and sr ca ratios the co3 ion effect is limited however only to aragonite saturation levels dco3 aragonite below 15 mmol kg 1 above this level temperature exerts a dominant effect accordingly we propose that mg ca and sr ca in h elegans tests can be used to reconstruct thermocline temperatures only in waters oversaturated with respect to the mineral aragonite using the following relationships mg ca 0 034 0 002 bwt 0 96 0 03 and sr ca 0 060 0 002 bwt 1 53 0 03 for dco3 aragonite 1 5mmol kg 1 the standard error associated with these equations is about 1 1 c reconstruction of deeper water temperatures is complicated because in undersaturated waters changes in mg ca and sr ca ratios reflect a combination of changes in co3 and bwt overall we find that sr ca rather than mg ca in h elegans may be a more accurate proxy for reconstructing paleotemperatures

cretaceous and early tertiary climates of antarctica evidence from fossil wood abstract fossil wood is abundant in cretaceous and early tertiary sediments of the northern antarctic peninsula region the wood represents the remains of vegetation that once grew in high palaeolatitudes when the polar regions were warmer during former greenhouse climates fossil wood is a unique data store of palaeoclimate information analyses of growth rings and anatomical characters in fossil wood provide important information about temperature rainfall seasonality and climate trends for this time period in antarctica climate signals from fossil wood supported by sedimentary and geochemical evidence indicate a trend of cool climates during the early cretaceous followed by peak warmth during the coniacian to early campanian narrower growth rings suggest that the climate cooled during the maastrichtian and palaeocene cool wet and possibly seasonal climates prevailed at this time with tentatively estimated mean annual temperatures mats falling from 7 c to 4 8 c respectively determined from dicotyledonous dicot wood anatomy the late palaeocene early eocene was once again warm with estimated mats of 7 15 c from dicot wood analysis but conditions subsequently deteriorated through the latter part of the eocene when cold seasonal climates developed ultimately leading to the onset of cenozoic ice sheets and the elimination of vegetation from most of antarctica

coupled greenhouse warming and deep sea acidification in the middle eocene 1 the middle eocene climatic optimum meco is an enigmatic warming event that represents an abrupt reversal in long term cooling through the eocene in order to further assess the timing and nature of this event we have assembled stable isotope and calcium carbonate concentration records from multiple deep sea drilling project and ocean drilling program sites for the time interval between 43 and 38 ma revised stratigraphy at several sites and compilation of 18o records place peak warming during the meco event at 40 0 ma chron c18n 2n the identification of the 18o excursion at sites in different geographic regions indicates that the climatic effects of this event were globally extensive the total duration of the meco event is estimated at 500 ka with peak warming lasting 100 ka assuming minimal glaciation in the late middle eocene 4 6 c total warming of both surface and deep waters is estimated during the meco at the study sites the interval of peak warming at 40 0 ma also coincided with a worldwide decline in carbonate accumulation at sites below 3000 m depth reflecting a temporary shoaling of the calcite compensation depth the synchroneity of deep water acidification and globally extensive warming makes a persuasive argument that the meco event was linked to a transient increase in atmospheric pco2 the results of this study confirm previous reports of significant climatic instability during the middle eocene furthermore the direct link between warming and changes in the carbonate chemistry of the deep ocean provides strong evidence that changes in greenhouse gas concentrations exerted a primary control on short term climate variability during this critical period of eocene climate evolution

environmental change in the subtropics during the late middle eocene greenhouse and global implications 1 oxygen isotope records from odp site 1052 blake nose subtropical north atlantic ocean indicate significant short term high amplitude variability up to 1 4 in about 2500 to 4000 years during the late middle eocene 37 9 37 5 ma these variations reflect a combination of changes in sea surface temperature and the oxygen isotope composition of the regional seawater in order to independently evaluate the magnitude of sst changes at blake nose and better understand the nature of environmental change during the late middle eocene we present planktonic foraminiferal mg ca data combined with 18o data from the same samples the calculated mg ca paleotemperatures indicate a decrease in ssts over the study interval from 33 to 28 c at the same time that previously published foraminiferal 18ocalcite values from the same samples also decrease thus the 18ocalcite values must reflect a significant component of seawater 18o change in order to reconcile the opposite paleotemperature trends reflected by both proxies calculated 18oseawater values decreased from 3 at 37 83 ma to 2 at 37 6 ma the combined trends of the sst and 18oseawater cannot be explained by an increase of continental ice over this time interval instead the data favor an overall weakening of the hydrological cycle as global climate transitioned from the greenhouse to icehouse

planktic foraminiferal dissolution in the twilight zone abstract calcite dissolution of planktic foraminifers that settle from the surface ocean to depths has been assessed using the weight size relationship of tests and correlated to carbonate ion concentration co 3 2 of ambient sea water globigerina bulloides and globigerinita glutinata were sampled from the north atlantic and the arabian sea during different seasons spring and fall and the monsoons respectively test weight has been determined for single tests from narrow size classes 250 8 m and 300 7 m minimum test diameter initial test weight of both species in surface waters differs between regions and seasons weight loss of settling tests in the twilight zone between 100 and 1000 m water depths averaged 19 below the twilight zone 1000 2500 m no weight loss occurs on average and tests may even gain weight remineralization of settling planktic foraminiferal tests is most pronounced at maximum co 3 2 accordingly strong dissolution occurs in the twilight zone at the depth of maximum decrease in co 3 2 it is assumed that dissolution of planktic foraminiferal calcite is caused by co 3 2 under saturation inside the test buffered by diffusive exchange of co 3 2 ions with the ambient sea water through the pores and aperture consequently reconstruction of small scale differences in seawater co 3 2 from test weight alone is not feasible and systematic correlation between test weight and co 3 2 of the ambient sea water is statistically not significant at constant co 3 2 remineralization cannot be deduced from test weight neither at high nor low co 3 2 saturation in total our data suggest that the global vertical planktic foraminiferal caco 3 flux is about 19 lower than calculated by schiebel 2002 planktic foraminiferal sedimentation and the marine calcite budget global biogeochemical cycles 16 4 1065 doi 10 1029 2001gb001459

testing the cenozoic multisite composite δ18o and δ13c curves new monospecific eocene records from a single locality demerara rise ocean drilling program leg 207 until recently very few high quality deep ocean sedimentary sections of eocene age have been available consequently our understanding of eocene paleoceanography has become heavily reliant on composite records patched together from multiple sites in different ocean basins and generated using multiple taxa potential sources of local noise in the global signal here we test the reliability of the early to middle eocene composite 18o and 13c stratigraphies zachos et al 2001 by generating new monospecific records in benthic foraminiferal calcite from a single locality demerara rise in the tropical western atlantic ocean drilling program leg 207 we present new stable isotope correction factors for commonly used eocene benthic foraminiferal species we find that interspecies isotopic offsets are constant across the isotopic range supporting the notion that the inconstant intertaxa offsets reported elsewhere result from mixing species within genera in general the 18o stratigraphy from demerara rise supports the validity of the eocene 18o composite while revealing a temporary warming punctuating middle eocene cooling this warming may correspond to the so called middle eocene climatic optimum previously documented in the southern ocean the composite and demerara rise records for 13c differ substantially by removing the intersite and intertaxa sources of uncertainty in 13c we obtain a clearer picture of carbon cycling during the eocene secular change in interocean 13c gradients through the eocene reveals that intervals of climatic warmth especially the early eocene are associated with very small water mass ageing gradients

timing and climatic consequences of the opening of drake passage age estimates for the opening of drake passage range from 49 to 17 million years ago ma complicating interpretations of the relationship between ocean circulation and global cooling secular variations of neodymium isotope ratios at agulhas ridge southern ocean atlantic sector suggest an influx of shallow pacific seawater approximately 41 ma the timing of this connection and the subsequent deepening of the passage coincide with increased biological productivity and abrupt climate reversals circulation productivity linkages are proposed as a mechanism for declining atmospheric carbon dioxide these results also indicate that drake passage opened before the tasmanian gateway implying the late eocene establishment of a complete circum antarctic pathway

carbonate ion effect on mg ca sr ca and stable isotopes on the benthic foraminifera oridorsalis umbonatus off namibia abstract we investigate the influence of carbonate system parameters carbonate ion concentration co32 carbonate ion saturation co32 on the trace element and stable isotope ratios in the endobenthic foraminifera oridorsalis umbonatus data from modern core top samples from the namibian continental slope suggest that the shell composition of this species is influenced by the chemistry of the pore water for these organic rich sediments the impact of ocean bottom water properties on both pore water and shell chemistry is surprisingly small sr ca correlates positively with co32 and to a lesser extent with co32 which is opposed to previous results a co32 decrease of 10 mol kg leads to an increase of 0 05 mmol mol in sr ca we observe a correlation between shell 18o corrected for temperature and 18o seawater and co32 however the variability of the corrected 18o is close to the analytical limit no clear dependences were observed for 13c and mg ca

early cenozoic benthic foraminiferal isotopes species reliability and interspecies correction factors 1 oxygen and carbon isotope records are important tools used to reconstruct past ocean and climate conditions with those of benthic foraminifera providing information on the deep oceans reconstructions are complicatedby interspecies isotopic offsets that result from microhabitat preferences carbonate precipitation in isotopically distinct environments and vital effects species specific metabolic variation in isotopic fractionation we provide correction factors for early cenozoic benthic foraminifera commonly used for isotopic measurements cibicidoides spp nuttallides truempyi oridorsalis spp stensioina beccariiformis hanzawaia ammophila and bulimina spp showing that most yield reliable isotopic proxies of environmental change the statistical methods and larger data sets used in this study provide more robust correction factors than do previous studies interspecies isotopic offsets appear to have changed through the cenozoic either 1 as a result of evolutionary changes or 2 as an artifact of different statistical methods and data set sizes used to determine the offsets in different studies regardless of the reason the assumption that isotopic offsets have remained constant through the cenozoic has introduced an 1 2 c uncertainty into deep sea paleotemperature calculations in addition we compare multiple species isotopic data from a western north atlantic section that includes the paleocene eocene thermal maximum to determine the most reliable isotopic indicator for this event we propose that oridorsalis spp was the most reliable deepwater isotopic recorder at this location because it was best able to withstand the harsh water conditions that existed at this time it may be the best recorder at other locations and for other extreme events also

ocean overturning since the late cretaceous inferences from a new benthic foraminiferal isotope compilation 1 benthic foraminiferal oxygen isotopic d 18 o and carbon isotopic d 13 c trends constructed from compilations of data series from multiple ocean sites provide one of the primary means of reconstructing changes in the ocean interior these records are also widely used as a general climate indicator for comparison with local and more specific marine and terrestrial climate proxy records we present new benthic foraminiferal d 18 o and d 13 c compilations for individual ocean basins that provide a robust estimate of benthic foraminiferal stable isotopic variations to 80ma andtentatively to 110ma first order variations ininterbasinal isotopicgradients delineate transitions from interior ocean heterogeneity during the late cretaceous 65 ma to early paleogene 35 65 ma homogeneity and a return to heterogeneity in the late paleogene early neogene 35 0 ma we propose that these transitions reflect alterations in a first order characteristic of ocean circulation the ability of winds to make water in the deep ocean circulate we document the initiation of large interbasinal d 18 o gradients in the early oligocene and link the variations in interbasinal d 18 o gradients from the middle eocene to oligocene with the increasing influence of wind driven mixing due to the gradual tectonic opening of southern ocean passages and initiation and strengthening of the antarctic circumpolar current the role of wind driven upwelling possibly associated with a tethyan circumequatorial current in controlling late cretaceous interior ocean heterogeneity should be the subject of further research

impacts of orbital forcing and atmospheric carbon dioxide on miocene ice sheet expansion the processes causing the middle miocene global cooling which marked the earth s final transition into an icehouse climate about 13 9 million years ago myr ago 1 4 remain enigmatic tectonically driven circulation changes 5 6 and variations in atmospheric carbon dioxide levels 7 8 have been suggested as driving mechanisms but the lack of adequately preserved sedimentary successions has made rigorous testing of these hypotheses difficult here we present high resolution climate proxy records covering the period from 14 7 to 12 7 million years ago from two complete sediment cores from the northwest and southeast subtropical pacific ocean using new chronologies through the correlation to the latest orbital model 9 we find relatively constant low summer insolation over antarctica coincident with declining atmospheric carbon dioxide levels at the time of antarctic ice sheet expansion and global cooling suggesting a causal link we surmise that the thermal isolation of antarctica played a role in providing sustained long term climatic boundary conditions propitious for ice sheet formation our data document that antarctic glaciation was rapid taking place within two obliquity cycles and coincided with a striking transition from obliquity to eccentricity as the drivers of climatic change

continental ice in greenland during the eocene and oligocene the eocene and oligocene epochs approximately 55 to 23 million years ago comprise a critical phase in earth history an array of geological records supported by climate modelling indicates a profound shift in global climate during this interval from a state that was largely free of polar ice caps to one in which ice sheets on antarctica approached their modern size however the early glaciation history of the northern hemisphere is a subject of controversy here we report stratigraphically extensive ice rafted debris including macroscopic dropstones in late eocene to early oligocene sediments from the norwegian greenland sea that were deposited between about 38 and 30 million years ago our data indicate sediment rafting by glacial ice rather than sea ice and point to east greenland as the likely source records of this type from one site alone cannot be used to determine the extent of ice involved however our data suggest the existence of at least isolated glaciers on greenland about 20 million years earlier than previously documented at a time when temperatures and atmospheric carbon dioxide concentrations were substantially higher