north atlantic current variability through marine isotope stage m2 circa 3 3 ma during the mid pliocene 1 the mid pliocene was an episode of prolonged global warmth and strong north atlantic thermohaline circulation interrupted briefly at circa 3 30 ma by a global cooling event corresponding to marine isotope stage mis m2 paleoceanographic changes in the eastern north atlantic have been reconstructed between circa 3 35 and 3 24 ma at deep sea drilling project site 610 and integrated ocean drilling program site 1308 mg ca ratios and 18o from globigerina bulloides are used to reconstruct the temperature and relative salinity of surface waters and dinoflagellate cyst assemblages are used to assess variability in the north atlantic current nac our sea surface temperature data indicate warm waters at both sites before and after mis m2 but a cooling of 2 3 c during mis m2 a dinoflagellate cyst assemblage overturn marked by a decline in operculodinium centrocarpum reflects a southward shift or slowdown of the nac between circa 3 330 and 3 283 ma reducing northward heat transport 23 35 ka before the global ice volume maximum of mis m2 this will have established conditions that ultimately allowed the greenland ice sheet to expand leading to the global cooling event at mis m2 comparison with an ice rafted debris record excludes fresh water input via icebergs in the northeast atlantic as a cause of nac decline the mechanism causing the temporary disruption of the nac may be related to a brief reopening of the panamanian gateway at about this time

from greenhouse to icehouse organic walled dinoflagellate cysts as paleoenvironmental indicators in the paleogene abstract dinoflagellates are an important component of the extant eukaryotic plankton their organic walled hypnozygotic cysts dinocysts provide a rich albeit incomplete history of the group in ancient sediments building on pioneering studies of the late 1970s and 1980s recent drilling in the southern ocean has provided a wealth of new dinocyst data spanning the entire paleogene such multidisciplinary studies have been instrumental in refining existing and furnishing new concepts of paleogene paleoenvironmental and paleoclimatic reconstructions by means of dinocysts because dinocysts notably exhibit high abundances in neritic settings dinocyst based environmental and paleoclimatic information is important and complementary to the data derived from typically more offshore groups as planktonic foraminifera coccolithophorids diatoms and radiolaria by presenting case studies from around the globe this contribution provides a concise review of our present understanding of the paleoenvironmental significance of dinocysts in the paleogene 65 25 ma representing earth s greenhouse icehouse transition this episode holds the key to the understanding of extreme transient climatic change we discuss the potential of dinocysts for the reconstruction of paleogene sea surface productivity temperature salinity stratification and paleo oxygenation along with their application in sequence stratigraphy oceanic circulation and general watermass reconstructions

the role of carbon dioxide during the onset of antarctic glaciation earth s modern climate characterized by polar ice sheets and large equator to pole temperature gradients is rooted in environmental changes that promoted antarctic glaciation 33 7 million years ago onset of antarctic glaciation reflects a critical tipping point for earth s climate and provides a framework for investigating the role of atmospheric carbon dioxide co2 during major climatic change previously published records of alkenone based co2 from high and low latitude ocean localities suggested that co2 increased during glaciation in contradiction to theory here we further investigate alkenone records and demonstrate that antarctic and subantarctic data overestimate atmospheric co2 levels biasing long term trends our results show that co2 declined before and during antarctic glaciation and support a substantial co2 decrease as the primary agent forcing antarctic glaciation consistent with model derived co2 thresholds

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

late eocene to early oligocene dinoflagellate cysts from the priabonian type area northeast italy biostratigraphy and paleoenvironmental interpretation abstract marginal marine late eocene through early oligocene dinoflagellate cyst successions have been studied from the type area of the priabonian stage northeast italy the results allow the recognition of dinoflagellate zones previously defined in bio and magnetostratigraphically well calibrated pelagic sequences from central italy thus providing a first order correlation of the priabonian stage to the standard chronostratigraphic scale with unprecedented precision within this detailed biostratigraphic framework successive shifts in the composition of the dinoflagellate cyst assemblages are interpreted in terms of sea level and sea surface temperature sst fluctuations the evaluation of ecologically and sedimentary controlled changes in the composition of dinoflagellate cyst assemblages in combination with sequence stratigraphic analysis allows the reconstruction of third and fourth order sea level fluctuations the third order sea level fluctuations appear to correspond to exxon cycles ta4 1 4 5 the stratigraphically and palaeoenvironmentally important late eocene dinoflagellate cyst species glaphyrocysta priabonensis sp nov is formally described

global vegetation dynamics and latitudinal temperature gradients during the mid to late miocene 15 97 5 33 ma a 617 site palaeobotanical dataset for the mid to late miocene is presented this dataset is internally consistent and provides a comprehensive overview of vegetational change from 15 97 to 5 33 ma the palaeobotanical dataset has been translated into the biome4 classification scheme to enable direct comparison with climate model outputs the vegetation change throughout the langhian seravallian tortonian and messinian is discussed the data shows that the langhian which includes the end of the mid miocene climatic optimum represents a world significantly warmer than today the high northern latitudes were characterised by cool temperate forests the mid latitudes by warm temperate mixed forests the tropics by tropical evergreen broadleaf forests and antarctica by tundra shrub vegetation cool temperate mixed forest existed during the seravallian in the high northern latitudes a reduction in warm temperate mixed forests in the mid latitudes and a loss of tundra on antarctica was noted tortonian vegetation distribution indicates that further cooling had occurred since the seravallian the major changes in vegetation include the first evidence for cold taiga forest in the high northern latitudes and a further reduction of warm temperate mixed forests by the messinian this cooling trend had eliminated warm temperate mixed forests from the western usa and australia and had formed mid latitude deserts despite the cooling trend throughout the mid to late miocene the vegetation distribution of all four reconstructed stages reflect the vegetation of a world warmer than the pre industrial conditions the latitudinal distribution of bioclimatic zones suggests that the latitudinal temperature gradient for the langhian would have been significantly shallower than at present and has gradually but asymmetrically become more modern towards the end of the miocene first the southern hemisphere distribution of bioclimatic zones became more modern probably due to the climatic effects of a fully glaciated antarctica the northern hemisphere bioclimatic zone gradient continued to be shallower than modern throughout the miocene and slowly became more modern by the messinian

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

effects of ice coverage and ice rafted material on sedimentation in the fram strait as little is known about pelagic sedimentation processes in arctic environments1 the interpretation of biological and chemical processes as well as the reconstruction of ancient conditions including those in the glacial north atlantic is difficult here we provide sediment trap results which show that the position of the sea ice boundary significantly influences the particle flux the seasonal variability of the particle flux differed markedly in the various sediment trap sites in fram strait depending on the behaviour of the sea ice under complete ice cover sedimentation is very low whereas maximum sedimentation is found at the ice margin the highest particle flux observed showing a large lithogenic component was observed at the ice edge where the water was warmer 2 c we find that high biogenic opal fluxes are characteristic of the summer ice margin indicating that the sedimentary record of opal fluxes may allow the position of ice margins in the past to be reconstructed

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

shifting ocean carbonate chemistry during the eocene oligocene climate transition implications for deep ocean mg ca paleothermometry to date no conclusive evidence has been identified for intermediate or deep water cooling associated with the 1 parts per thousand benthic delta o 18 increase at the eocene oligocene transition eot when large permanent ice sheets first appeared on antarctica interpretation of this isotopic shift as purely ice volume change necessitates bipolar glaciation in the early oligocene approaching that of the last glacial maximum to test this hypothesis it is necessary to have knowledge about deep water temperature which previous studies have attempted to reconstruct using benthic foraminiferal mg ca ratios however it appears likely that contemporaneous changes in ocean carbonate chemistry compromised the mg ca temperature sensitivity of benthic foraminifera at deep sites new geochemical proxy records from a relatively shallow core odp site 1263 estimated paleodepth of 2100 m on the walvis ridge reveal that carbonate chemistry change across the eot was not limited to deep sites but extended well above the lysocline critically limiting our ability to obtain reliable estimates of deep ocean cooling during that time benthic li ca measurements used as a proxy for co32 suggest that co32 increased by similar to 29 mu mol kg at site 1263 across the eot and likely impacted benthic foraminiferal mg ca a co32 benthic mg ca relationship is most apparent during the early eot when the overall increase in co32 is interrupted by an apparent dissolution event planktonic d18o and mg ca records suggest no change in thermocline temperature and a delta o 18 seawater increase of up to 0 6 parts per thousand at this site across the eot consistent with previous estimates and supporting the absence of extensive bipolar glaciation in the early oligocene

orbitally driven insolation forcing on holocene climate trends evidence from alkenone data and climate modeling a global spatial pattern of long term sea surface temperature sst trends over the last 7000 years is explored using a comparison of alkenone derived sst records with transient ensemble climate simulations with a coupled atmosphere ocean circulation model under orbitally driven insolation forcing the spatial trend pattern both in paleo sst data and in model results shows pronounced global heterogeneity generally the extratropics cooled while the tropics experienced a warming during the middle to late holocene we attribute these divergent holocene climate trends to seasonally opposing insolation changes furthermore climate mode changes similar to the arctic north atlantic oscillation are superimposed on the prevalent pattern it is concluded that nonlinear changes in the entire seasonal cycle of insolation played a dominant role for the temporal evolution of holocene surface temperatures for understanding of marine proxy data apart from the dominance of summer insolation in high latitudes a notable shift in the maximum insolation of the year in low latitudes has to be taken into account which may influence timing of phytoplankton production and thus alters the seasonal origin of temperature signals recorded in the proxies

60fe 60ni and 53mn 53cr isotopic systems in sulfides from unequilibrated enstatite chondrites abstract in situ measurements of 60 fe 60 ni and 53 mn 53 cr isotopic systems with an ion microprobe have been carried out for sulfide assemblages from unequilibrated enstatite chondrites uecs evidence for the initial presence of 60 fe has been observed in nine sulfide inclusions from three uecs alha77295 mac88136 and qingzhen the inferred initial 60 fe 56 fe 60 fe 56 fe 0 ratios show a large variation range from 2 10 7 to 2 10 6 the sulfide inclusions with high fe ni ratios yield 60 fe 56 fe 0 ratios of 2 7 10 7 similar to most of the 60 fe 56 fe 0 values of troilite and pyroxene observed in unequilibrated ordinary chondrites uocs inclusions with high inferred 60 fe 56 fe 0 ratios 1 2 10 6 have low fe ni ratios and the magnitude of the 60 ni excesses is similar in two mac88136 assemblages in spite of a difference of a factor of two in their fe ni ratios the inferred high 60 fe 56 fe 0 ratios were probably the result of fe ni re distribution in the sulfides during later alteration processes the 53 mn 53 cr system was measured in five of the sulfide assemblages that were examined for their 60 fe 60 ni systematics the 53 mn 53 cr isochrons yielded variable initial 53 mn 55 mn 53 mn 55 mn 0 ratios from 2 7 10 7 there is no obvious correlation between the 60 fe 56 fe 0 and 53 mn 55 mn 0 ratios the variable 53 mn 53 cr isochrons probably also indicate later disturbance to the isotopic systems in these sulfides even though no chronological information can be extracted from the 60 fe 60 ni and 53 mn 53 cr systems in these uec sulfides our results indicate that 60 fe was present in the enstatite chondrite formation region of the early solar system

the heartbeat of the oligocene climate system a 13 million year continuous record of oligocene climate from the equatorial pacific reveals a pronounced heartbeat in the global carbon cycle and periodicity of glaciations this heartbeat consists of 405 000 127 000 and 96 000 year eccentricity cycles and 1 2 million year obliquity cycles in periodically recurring glacial and carbon cycle events that climate system response to intricate orbital variations suggests a fundamental interaction of the carbon cycle solar forcing and glacial events box modeling shows that the interaction of the carbon cycle and solar forcing modulates deep ocean acidity as well as the production and burial of global biomass the pronounced 405 000 year eccentricity cycle is amplified by the long residence time of carbon in the oceans

complex response of dinoflagellate cyst distribution patterns to cooler early oligocene oceans previous studies have made extensive use of dinoflagellate cysts to reconstruct past sea surface temperature sst analysis of associations of dinoflagellate cysts using two new ocean datasets for the mid eocene bartonian and early oligocene rupelian reveals clear latitudinally constrained distributions for the bartonian but unexpected changes in their rupelian distribution a significant number of species with low and mid latitude northern hemisphere occurrences in the bartonian extend their northward ranges in the rupelian including some forms characterised as warm water by previous studies this suggests either that dinoflagellates are faithfully tracking a complex oceanographic response to rupelian cooling or that dinoflagellate sensitivity adaptability to a range of ecological variables means that at a global scale their distributions are not primarily controlled by sea surface temperature variability previous use of dinoflagellate cysts for palaeoclimate work has relied on rather subjective and inconsistent identification of warm and cold water forms rather than comprehensive analysis of community associations at the global scale it is clear from this study that a better understanding of the palaeo ecology of dinoflagellates and their cysts is required rupelian dinoflagellate cyst distribution may reflect changes in a range of environmental variables linked to early oligocene climate cooling for example changes in nutrient fluxes triggered by glacially induced base level fall complex reorganisation of ocean current systems between the bartonian and rupelian or muted changes to rupelian summer ssts in the northern hemisphere that have previously been reported many extant dinoflagellate species also exhibit relatively broad temperature tolerance moreover they have potentially extensive cryptic diversity and are able to produce dormant cysts during short lived environmental deterioration all of which may act to limit the value of undifferentiated dinoflagellate cyst assemblages for identifying climate signals

middle eocene regional climate instability evidence from the western north atlantic high resolution 3 k y d 18 o records from middle eocene mixed layer dwelling planktonic foraminifera from the western north atlantic show pronounced 1 variability the magnitude of change is greater than that seen in open ocean pleistocene records but could not have been caused by ice volume and or sea level fluctuations instead the oxygen isotope shifts resulted primarily from large oscillations in sea surface temperatures and indicate that the regional paleoceanography of the middle eocene western north atlantic was not consistently warm or stable the large shifts in sea surface temperatures could reflect variations in the position of the gulf stream relative to blake nose or variations in upwelling intensity

atmospheric carbon dioxide through the eocene oligocene climate transition geological and geochemical evidence1 2 3 indicates that the antarctic ice sheet formed during the eocene oligocene transition4 33 5 34 0 million years ago modelling studies5 6 suggest that such ice sheet formation might have been triggered when atmospheric carbon dioxide levels fell below a critical threshold of 750 p p m v but the timing and magnitude of relative to the evolution of the ice sheet has remained unclear here we use the boron isotope ph proxy7 8 on exceptionally well preserved carbonate microfossils from a recently discovered geological section in tanzania9 10 to estimate before during and after the climate transition our data suggest that a reduction in occurred before the main phase of ice growth followed by a sharp recovery to pre transition values and then a more gradual decline during maximum ice sheet growth was between 450 and 1 500 p p m v with a central estimate of 760 p p m v the ice cap survived the period of recovery although possibly with some reduction in its volume implying as models predict11 a nonlinear response to climate forcing during melting overall our results confirm the central role of declining in the development of the antarctic ice sheet in broad agreement with carbon cycle modelling12 and help to constrain mechanisms and feedbacks associated with the earth s biggest climate switch of the past 65 myr

variability of sea surface temperature and sea ice cover in the fram strait over the last two millennia abstract a sediment core located on the west spitzbergen margin in the fram strait 78 54 931 n 6 46 005 e water depth 1497 m was analyzed for its dinocyst content in order to reconstruct hydroclimatic variations of the last 2500 years the relative abundance of dinocyst taxa and principal component analysis show a major transition at about 300 cal years bp it is characterized by the disappearance of thermophilic taxa spiniferites mirabilis hyperacanthus and impagidinium sphaericum and the increase of polar subpolar taxa impagidinium pallidum and pentapharsodinium dalei sea surface temperature sst estimates suggest warmer conditions than present anomaly 2 c averaging at 7 c in summer until 300 cal years bp although cooling pulses are recorded around 1700 1500 1200 and 800 cal years bp the last 300 years were marked by a cooling from 7 6 to 3 5 c and sea ice cover increasing up to 7 months yr the results demonstrate that the fram strait area is sensitive to hydroclimatic variations notably with respect to sea ice and ssts which are linked to the relative strength of northward flow of north atlantic waters to the east and southward outflow of cold and fresh waters from the arctic ocean based on our data the warmest part of our record around 1320 cal years bp is the only interval of the last 2500 years that provides a possible analogue for the modern post ad 2000 interval which is characterized by sea ice free conditions

evidence for an earliest oligocene abrupt cooling in the surface waters of the southern ocean quantitative analysis of upper eocene upper oligocene calcareous nannofossil assemblages from five ocean drilling program sites in the atlantic and indian ocean sectors of the southern ocean reveals an abrupt increase in cool water taxa at the top of magnetic subchron c13r ca 35 9 ma coincident with an enrichment of 1 18 o in the planktonic foraminifers at these sites the synchrony of the abrupt increase in cool water taxa in the southern ocean renders this event a useful biostratigraphic datum at southern high latitudes this earliest oligocene cool water taxa increase was the sharpest and largest during the late eocene late oligocene interval and indicates a drop in surface water temperature of more than 3 c in the southern ocean this suggests that the earliest oligocene 18 o shift represents primarily a temperature signal a small portion 0 2 is attributable to a global ice volume increase

effects of the oligocene climatic events on the foraminiferal record from fuente caldera section spain western tethys abstract an expanded succession of upper priabonian upper eocene to chattian upper oligocene hemipelagic marls interbedded with turbiditic sandstone layers is present in the spanish fuente caldera section subbetic zone western tethys we analyzed foraminifera from this section quantitatively with emphasis on biostratigraphy and paleoecology benthic foraminifera indicate an upper to possibly upper middle bathyal depth of deposition for most of the studied section with paleobathymetric analysis made difficult because of the common presence of shallow water taxa some reworked by turbidites and others epiphytic taxa which may have been transported by turbidites or by floating plant material we identified three major biotic and paleoenvironmental events 1 the major planktonic foraminiferal turnover across the eocene oligocene boundary which includes several first and last occurrences as well as a decrease in the percentage of surface water dwellers possibly linked to global cooling 2 a dramatic sea level drop indicated by the presence of a 37 m thick sequence of calcarenites lower half of planktonic foraminiferal zone o2 31 5 ma with abundant trace fossils and allochthonous foraminifera this sea level fall which triggered erosion of material in shallow marine settings and transport by turbidity currents into the basin apparently post dated the major glacial expansion on the antarctic continent oi1 33 7 ma and predated the later major expansion oi2 through oi2b 27 30 5 ma thus may have been tectonically controlled 3 a warming event starting in the chattian lowermost part of zone o6 27 1 ma which could be correlated to the globally recognised late oligocene warming event but apparently started somewhat earlier 27 1 ma as compared to 26 5 ma

deciphering the palaeoecology of late pliocene and early pleistocene dinoflagellate cysts abstract in an attempt to document the palaeoecological affinities of individual extant and extinct dinoflagellate cysts late pliocene and early pleistocene dinoflagellate cyst assemblages have been compared with geochemical data from the same samples mg ca ratios of globigerina bulloides were measured to estimate the spring summer sea surface temperatures from four north atlantic iodp dsdp sites currently our pliocene pleistocene database contains 204 dinoflagellate cyst samples calibrated to geochemical data this palaeo database is compared with modern north atlantic and global datasets the focus lies in the quantitative relationship between mg ca based i e spring summer sea surface temperatures sstmg ca and dinoflagellate cyst distributions in general extant species are shown to have comparable spring summer sst ranges in the past sstmg ca and today sst from world ocean atlas 2005 locarnini et al 2006 demonstrating that our new approach is valid for inferring spring summer sst ranges for extinct species for example habibacysta tectata represents sstmg ca values between 10 and 15 c when it exceeds 30 of the assemblage and invertocysta lacrymosa exceeds 15 when sstmg ca values are between 18 6 and 23 5 c however comparing pliocene and pleistocene sstmg ca values with present day summer values for the extant impagidinium pallidum suggests a greater tolerance of higher temperatures in the past this species occupies more than 5 of the assemblage at sstmg ca values of 11 6 17 9 c in the pliocene and pleistocene whereas present day summer ssts are around 1 7 to 6 9 c this observation questions the value of impagidinium pallidum as reliable indicator of cold waters in older deposits and may explain its bipolar distribution

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

recent changes in arctic ocean sea ice motion associated with the north atlantic oscillation examination of a new ice motion dataset of the arctic ocean over a recent eighteen year period 1978 1996 reveals patterns of variability that can be linked directly to the north atlantic oscillation the intensity of the icelandic low one of its centers of action modulates the sea level pressure distribution over a broad region of the arctic ocean and the greenland iceland norwegian and barents seas over the winters of 1988 through 1995 the oscillation has remained in its positive phase contributing to coherent large scale changes in the intensity and character of ice transport in the arctic ocean the significant changes include the weakening of the beaufort gyre the increase in ice export through the fram strait the increase in ice import from the barents kara seas the enhanced eastward transport of sea ice from the laptev sea the weakening of the transpolar drift stream and the reduction in ice extent in the nordic seas all of these changes affect the regional and total sea ice mass balance of the arctic ocean

cooling and ice growth across the eocene oligocene transition the eocene oligocene e o climate transition ca 34 ma marks a period of antarctic ice growth and a major step from early cenozoic greenhouse conditions toward today s glaciated climate state the transition is represented by an increase in deep sea benthic foraminiferal oxygen isotope 18o values occurring in two main steps that reflect the temperature and 18o of seawater existing benthic mg ca paleotemperature records do not display a cooling across the transition possibly reflecting a saturation state effect on benthic foraminiferal mg ca ratios at deep water sites here we present data from exceptionally well preserved foraminifera deposited well above the calcite compensation depth that provide the first proxy evidence for an 2 5 c ocean cooling associated with the ice growth this permits interpretation of e o 18o records without invoking northern hemisphere continental scale ice

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

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

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

dinoflagellate cyst stratigraphy of the eocene oligocene transition in central italy abstract eight dinoflagellate cyst zones based on the massignano and monte cagnero sections in central italy provide high resolution control for the eocene oligocene e o transition most of these zones have been recognized in the time equivalent contessa highway section and are calibrated against previously established magneto and biostratigraphies the invasion of the mediterranean area by several higher latitude dinoflagellate taxa marks the e o boundary as characterized by the last occurrence of the hantkeninids planktic foraminifers calibrated against a horizon just above the youngest normal polarity event within chron c1 3r quantitative and qualitative dinoflagellate events across the e o boundary allow the recognition of warmer and cooler successive intervals of sea surface temperature in addition to apparent sea level fluctuations our data indicate that latest eocene warm conditions and a sea level highstand were rapidly replaced by short term cooler conditions and a lowstand across the e o boundary horizon following a shortterm warmer interval and a highstand during the earliest oligocene a second cool and lowstand episode occurred this cool interval was of greater magnitude and duration than the one at the e o boundary horizon and may correspond to the globally recognized cooling event reported from the basal part of chron c1 3n

a tortonian late miocene 11 61 7 25 ma global vegetation reconstruction for the tortonian age of the miocene epoch 11 6 7 25 ma we present a global palaeobotanical and palaeoecologically based vegetation dataset combined with a best fit late miocene climate vegetation model experiment to create an advanced global data model hybrid biome reconstruction this new palaeoecological database and global vegetation reconstruction can be used both for the purposes of validating future palaeoclimate model simulations as well as a land cover dataset to initialise palaeoclimate modelling experiments our tortonian reconstruction shows significant changes in the distribution of vegetation compared to modern natural vegetation for example in contrast to the modern scenario in the northern hemisphere boreal forests reached 80 n and temperate forests were present above 60 n warm temperate forests covered much of europe coastal north america and south east asia our reconstruction shows a spread of temperate savanna in central usa the middle east and on the tibetan plateau evidence for arid deserts is sparse with the exception of the atacama region south america areas that exhibit arid desert today in the tortonian were instead covered by shrublands grasslands savannas and woodlands the extent of tropical forests in south america was likely reduced but expanded in the indian sub continent and east africa this pattern of global vegetation in the late miocene suggests a warmer and wetter world which is supported by the pattern of climate anomalies predicted by our best fit palaeoclimate vegetation model experiment global mean annual temperature may have been as much as 4 5 c higher than present day with many regions experiencing higher than modern amounts of precipitation over the annual cycle the pattern of temperature and precipitation change reconstructed palaeobotanically and predicted within our climate model experiment infers a global forcing agent on tortonian climate e g such as elevated concentrations of greenhouse gases to explain the observed and modelled climate anomalies this is in contrast to current proxy records of tortonian atmospheric co2 which range from last glacial maximum to mid 20th century levels

late albian dinoflagellate cyst paleobiogeography as indicator of asymmetric sea surface temperature gradient on both hemispheres with southern high latitudes warmer than northern ones abstract late albian temperature sensitive dinoflagellate cysts are characterized in order to better understand mid cretaceous sea surface temperature gradients distribution maps of thirty seven species recovered from one hundred fifty outcrops and deep sea drilling holes odp dsdp sites located from low and high paleolatitudes over the two hemispheres 75 n 70 s are encountered fifty years of published data available in eighty seven articles have been considered and synthesized using a database coupled with a geographical information system gis the continuous and disjoint biogeographic patterns of dinocyst species along latitudes define seven climatic belts four in the northern hemisphere high mid high mid low low latitude belts and three in the southern hemisphere low mid low mid high latitude belts dinocysts restricted along latitudes are temperature sensitive species limit ranges of temperature sensitive dinocysts of mid low and mid high latitude belts reveal mixing belts located at 40 45 n and 50 70 s they represent major palaeofrontal systems as paleosubtropical fronts with strongly mixed water column the northern frontal system 40 45 n was located as in the modern ocean the large southern frontal system 50 s 70 s was 10 20 poleward to antarctica semi quantitative temperature range limits for mid cretaceous dinoflagellates and sst gradients in the two hemispheres are suggested by setting dinocyst climatic belts against estimated 18o temperature curve from fish teeth a paleoecological classification is suggested latitudinal distribution of extant temperature sensitive dinoflagellate cysts follows the asymmetric modern temperature gradient asymmetric latitudinal ranges of late albian dinocyst species of mid low latitude belts restricted between 45 n and 70 s demonstrate asymmetric temperature gradients with southern high latitudes being warmer than northern high latitudes

mixing and convection in the greenland sea from a tracer release experiment convective vertical mixing in restricted areas of the subpolar oceans such as the greenland sea is thought to be the process responsible for forming much of the dense water of the ocean interior1 2 deep water formation varies substantially on annual and decadal timescales3 4 5 and responds to regional climate signals such as the north atlantic oscillation6 7 its variations may therefore give early warning of changes in the thermohaline circulation that may accompany climate change8 here we report direct measurements of vertical mixing by convection and by turbulence from a sulphur hexafluoride tracer release experiment in the central greenland sea gyre in summer we found rapid turbulent vertical mixing of about 1 1 cm2 s 1 in the following late winter part of the water column was mixed more vigorously by convection indicated by the rising and vertical redistribution of the tracer patch in the centre of the gyre at the same time mixing outside the gyre centre was only slightly greater than in summer the results suggest that about 10 of the water in the gyre centre was vertically transported in convective plumes which reached from the surface to at their deepest 1 200 1 400 m convection was limited to a very restricted area however and smaller volumes of water were transported to depth than previously estimated9 our results imply that it may be the rapid year round turbulent mixing rather than convection that dominates vertical mixing in the region as a whole

holocene cooling culminates in sea ice oscillations in fram strait a reconstruction of holocene sea ice conditions in the fram strait provides insight into the palaeoenvironmental and palaeoceanographic development of this climate sensitive area during the past 8500 years bp organic geochemical analyses of sediment cores from eastern and western fram strait enable the identification of variations in the ice coverage that can be linked to changes in the oceanic and atmospheric circulation system by means of the sea ice proxy ip25 phytoplankton derived biomarkers and ice rafted detritus ird increasing sea ice occurrences are traced along the western continental margin of spitsbergen throughout the holocene which supports previous palaeoenvironmental reconstructions that document a general cooling a further significant ice advance during the neoglacial is accompanied by distinct sea ice fluctuations which point to short term perturbations in either the atlantic water advection or arctic water outflow at this site at the continental shelf of east greenland the general holocene cooling however seems to be less pronounced and sea ice conditions remained rather stable here a major neoglacial increase in sea ice coverage did not occur before 1000 years bp phytoplankton ip25 indices pip25 index are used for more explicit sea ice estimates and display a mid holocene shift from a minor sea ice coverage to stable ice margin conditions in eastern fram strait while the inner east greenland shelf experienced less severe to marginal sea ice occurrences throughout the entire holocene highlights biomarker and ird data give insight into holocene sea ice conditions in fram strait we find increasing sea ice coverage off west spitsbergen throughout the holocene oceanic atmospheric variability caused neoglacial sea ice fluctuations ice conditions along east greenland shelf remain rather stable until 1000 years bp

dinoflagellate based sea surface temperature reconstructions across the cretaceous tertiary boundary abstract quantitative analysis of organic walled dinoflagellate cyst dinocyst assemblages from closely spaced samples across the cretaceous tertiary boundary ktb at el kef nw tunisia caravaca se spain and stevns klint e denmark allows for reconstructions of sea surface temperature sst trends the combined dinocyst based sst curves indicate relatively stable warm conditions during the latest maastrichtian in contrast to strongly fluctuating and on average cooler conditions during the earliest danian in detail the results indicate cooling across the ktb immediately followed by an interval of pronounced warming the latter recorded in all studied sections two more cooling pulses may be recognized in the overlying interval followed by a gradual return to stable relatively warm conditions our data furthermore show that these ktb related climatic changes invoked distinct migration among organic walled cyst producing dinoflagellates a group not pushed to extinction at the ktb recordable in both hemispheres recent models predict periods varying between several months to 8 13 yr of global cooling impact winter and reduced solar transmission as a direct result of the chicxulub ktb impact followed by relatively long term excess co 2 related global warming our results are in line with such models but suggest that the impact related cooling phase may have lasted longer and that marked climatic instability continued to some 100 000 yrs following the ktb event s

increased seasonality through the eocene to oligocene transition in northern high latitudes a profound global climate shift took place at the eocene oligocene transition approximately 33 5 million years ago when cretaceous early palaeogene greenhouse conditions gave way to icehouse conditions during this interval changes in the earth s orbit and a long term drop in atmospheric carbon dioxide concentrations resulted in both the growth of antarctic ice sheets to approximately their modern size and the appearance of northern hemisphere glacial ice however palaeoclimatic studies of this interval are contradictory although some analyses indicate no major climatic changes others imply cooler temperatures increased seasonality and or aridity climatic conditions in high northern latitudes over this interval are particularly poorly known here we present northern high latitude terrestrial climate estimates for the eocene to oligocene interval based on bioclimatic analysis of terrestrially derived spore and pollen assemblages preserved in marine sediments from the norwegian greenland sea our data indicate a cooling of approximately 5 degrees c in cold month winter mean temperatures to 0 2 degrees c and a concomitant increased seasonality before the oi 1 glaciation event these data indicate that a cooling component is indeed incorporated in the delta 18 o isotope shift across the eocene oligocene transition however the relatively warm summer temperatures at that time mean that continental ice on east greenland was probably restricted to alpine outlet glaciers

sequence stratigraphic interpretations from palynofacies dinocyst and lithological data of upper eocene lower oligocene strata in southern mississippi and alabama u s gulf coast abstract this paper presents new information on the sequence stratigraphy of the upper eocene lower oligocene strata in southern mississippi and alabama based on palynological and lithological data from five sections by integrating lithological characteristics with palynofacies assemblages several dinocyst paleoecological groups the deflandrea group and the abundance of reworked dinocysts in samples paleobathymetric curves were reconstructed and used to revise the sequence stratigraphy of the area we identified a maximum flooding surface in the middle of the shubuta clay formation in southern mississippi and dated it as latest eocene in southern alabama the eocene oligocene boundary was placed within a condensed section representing about 0 19 ma and it coincided with the shubuta clay vicksburg group contact this condensed section is equivalent to the accumulation of the upper shubuta and red bluff formations in southern mississippi the forest hill mint spring contact which has been interpreted as a sequence boundary that merged with a transgressive surface does not correlate with the tejas a ta 4 3 4 4 sequence boundary of haq et al 1988 the pachuta marl and lower shubuta clay formations are constituents of a late eocene transgressive systems tract in southern mississippi but this systems tract extended to the shubuta clay vicksburg group contact in southern alabama the overlying early oligocene highstand systems tract consisted of the upper shubuta in mississippi and the red bluff bumpnose forest hill formations a thin sandstone in the mint spring was interpreted as a deposit of a possible lowstand systems tract above the sequence boundary in one southern mississippi section in general the mint spring marl and marianna limestone constituted a transgressive systems tract

a mid oligocene cooling oi 2b reflected in the dinoflagellate record and in depositional sequence architecture an integrated study from the eastern north sea basin abstract integrated micropaleontological dinoflagellate and foraminifera and 3d seismic studies of oligocene surfaces were carried out in the eastern north sea in order to investigate the influence of the climate on the evolution of depositional geometries and surface morphologies age indicative dinoflagellates allowed a correlation of the succession with the global time scale and thereby with published oxygen isotope curves temperature indicative dinoflagellate taxa furthermore allowed to infer paleoclimatic changes during the mid oligocene one of the surfaces studied on 3d seismic datasets shows features such as low angle landward directed onlaps incised valleys and pockmarks indicating a prominent relative sea level fall the cold water dinoflagellate svalbardella was recorded immediately above this surface the coincidence of a cold water indicator with this distinctive sequence boundary shows that deposition of this sequence was controlled by climatically induced sea level changes and that 3d seismic analysis combined with high resolution dinoflagellate analysis substantially improves the understanding of the depositional history and processes within the north sea basin the svalbardella event represents the oi 2b glaciation and coincides with the onshore nw european rupelian chattian boundary

polar front shift and atmospheric co2 during the glacial maximum of the early paleozoic icehouse our new data address the paradox of late ordovician glaciation under supposedly high pco2 8 to 22 pal preindustrial atmospheric level the paleobiogeographical distribution of chitinozoan mixed layer marine zooplankton biotopes for the hirnantian glacial maximum 440 ma are reconstructed and compared to those from the sandbian 460 ma they demonstrate a steeper latitudinal temperature gradient and an equatorwards shift of the polar front through time from 55 70 s to 40 s these changes are comparable to those during pleistocene interglacial glacial cycles in comparison with the pleistocene we hypothesize a significant decline in mean global temperature from the sandbian to hirnantian proportional with a fall in pco2 from a modeled sandbian level of 8 pal to 5 pal during the hirnantian our data suggest that a compression of midlatitudinal biotopes and ecospace in response to the developing glaciation was a likely cause of the end ordovician mass extinction

recent geographical distribution of organic walled dinoflagellate cysts in the southeast pacific 25 53 s and their relation to the prevailing hydrographical conditions abstract forty eight surface sediment samples from the southeast se pacific 25 53 s are investigated for the determination of the spatial distribution of organic walled dinoflagellate cysts along the western south american continental margin fifty five different taxa are recorded and reflect oceanic or coastal assemblages the oceanic assemblages are characterised by low cyst concentrations and the dominance of autotrophs while the coastal assemblages generally contain a higher number of cysts which are mainly produced by heterotrophic species highest cyst concentrations are observed in the active upwelling system offshore concepcion 35 37 s brigantedinium spp echinidinium aculeatum echinidinium granulatum delicatum and cysts of protoperidinium americanum dominate assemblages related to upwelling echinidinium aculeatum appears to be the best indicator for the presence of all year round active upwelling cells other protoperidinioid cysts may also occur in high relative abundances in coastal regions outside active upwelling systems if the availability of nutrients co responsible for the presence absence of their main food sources such as diatoms and other protists is sufficient the importance of nutrient availability as a determining environmental variable influencing cyst signals on a regional scale se pacific is demonstrated through statistical analyses of the data because of the importance of nutrients uncertainties about the outcomes of quantitative sea surface temperature sst reconstructions modern analogue technique based on dinoflagellate cysts may arise since no interaction between different hydrographical variables is considered in this approach the combination of the se pacific surface sample dataset with other published cyst data from the southern hemisphere resulted in a database which includes 350 samples the sh350 database this database is used to test the accuracy of the quantitative reconstructions by calculating and comparing the estimated versus observed values for each site an attempt to perform quantitative sst reconstructions on the last 25 cal ka of site odp1233 41 s 74 27 w is made and again stresses the importance of other environmental variables such as nutrient availability in determining the dinoflagellate cyst assemblages

the relationship between neogene dinoflagellate cysts and global climate dynamics abstract the neogene period 23 03 2 58 ma underwent a long term relatively gradual cooling trend culminating in the glacial interglacial climate of the quaternary palaeoclimate studies on the neogene have provided important information for understanding how modern patterns of atmospheric and oceanic circulation developed and how they may relate to wider environmental change here we use a newly created global database of neogene dinoflagellate cysts the tertiary oceanic parameters information system topis to investigate how dinoflagellate cysts recorded the cooling of neogene surface marine waters on a global scale species with warm and cold water preferences were determined from previously published literature and extracted from the database percentages of cold water species were calculated relative to the total number of species with known temperature preferences from each site and compared throughout the neogene at differing latitudes overall the percentage of cold water species increases gradually through the neogene this trend indicates a gradual global cooling that is comparable to that reported from other marine and terrestrial proxies this also demonstrates the use of dinoflagellate cysts in determining temperature change on both extended temporal and wide geographical scales the increase in the percentage of cold water species of dinoflagellate cysts recorded worldwide from the early and middle miocene to the late pliocene indicates a global scale forcing agent on neogene climate such as co2

advection of atlantic water to the western and northern svalbard shelf since 17 500 cal yr bp abstract the changes in flow and character of the warm atlantic water through the last 17 500 cal yr are reconstructed from the distribution of benthic foraminifera species planktonic and benthic foraminifera abundances stable oxygen isotopes and lithology in two cores from the western and northern shelf of svalbard the results show almost continuous presence of atlantic water at the shelf areas since 14 500 cal yr bp the bolling and allerod intervals stand out as periods of highest bottom waters temperatures the strong inflow of saline but chilled atlantic water during the early holocene was followed by cooling and freshening of the bottom waters during the mid and late holocene the two records reveal synchronous oceanographic changes that are closely tied to changes in the flow of atlantic water recorded further south in the nordic seas the early holocene warming was not just an effect of higher solar insolation but was also due to increased heat flux from the stronger atlantic water inflow driven by wind force and or thermohaline circulation

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

a high resolution study of holocene paleoclimatic and paleoceanographic changes in the nordic seas 1 high resolution records from images core md95 2011 in the eastern norwegian sea provide evidence for relatively large and small scale high latitude climate variability throughout the holocene during the early and mid holocene a situation possibly driven by consistent stronger westerlies increased the eastward influence of arctic intermediate and near surface waters for the late holocene a relaxation of the atmospheric forcing resulted in increased influence of atlantic water the main changes in holocene climate show no obvious connection to changing solar irradiance and spectral analysis reveals no consistent signature for any periodic behavior of holocene climate at millennial or centennial timescales there are however indications of consistent multidecadal variability

the eocene oligocene transition changes in sea level temperature or both abstract the eocene oligocene transition eot 34 ma reflects the onset of major antarctic glaciation the primary geochemical signature of the eot is two 300 kyr spaced shifts in increasing deep sea oxygen isotope values possibly reflecting both global cooling and or increasing ice volume a way to assess the respective contribution of continental ice is to quantify concomitant glacio eustatic sea level change this is usually expressed in relatively shallow marine depositional settings one potentially suitable region is in the vicentinian alps ne italy where marginal marine deposits document sea level changes during the eot by correlating stable isotope bio and magnetostratigraphic information between three distant regions we are able to relate the shallow marine sections to the pacific oxygen isotope record from ocean drilling program odp site 1218 of coxall et al 2005 microfacies sedimentological and biotic analysis suggests that associated with the first isotope shift eot 1 sea level fell 20 m and with the ultimate shift the oligocene isotope event 1 oi 1 sea level fell some 50 60 m distribution patterns of temperature sensitive dinoflagellates from a coeval central italian section reveal that the early stages of the eot were accompanied by sea surface cooling whereas no sustained cooling is noted in association with the oi 1 this suggests that the initial eot shift s reflect a mixed signal of ice volume and temperature whereas the oi 1 primarily reflects expansion of the antarctic cryosphere

the potential of organic walled dinoflagellate cysts for the reconstruction of past sea surface conditions in the southern ocean abstract in this study we investigate the potential of organic walled dinoflagellate cysts dinocysts as tools for quantifying past sea surface temperatures sst in the southern ocean for this purpose a dinocyst reference dataset has been formed based on 138 surface sediment samples from different circum antarctic environments the dinocyst assemblages of these samples are composed of phototrophic gonyaulacoid and heterotrophic protoperidinioid species that provide a broad spectrum of palaeoenvironmental information the relationship between the environmental parameters in the upper water column and the dinocyst distribution patterns of individual species has been established using the statistical method of canonical correspondence analysis cca among the variables tested summer sst appeared to correspond to the maximum variance represented in the dataset to establish quantitative summer sst reconstructions a modern analogue technique mat has been performed on data from three late quaternary dinocyst records recovered from locations adjacent to prominent oceanic fronts in the atlantic sector of the southern ocean these dinocyst time series exhibit periodic changes in the dinocyst assemblage during the last two glacial interglacial cycles during glacial conditions the relative abundance of protoperidinioid cysts was highest whereas interglacial conditions are characterised by generally lower cyst concentrations and increased relative abundance of gonyaulacoid cysts the mat palaeotemperature estimates show trends in summer sst changes following the global oxygen isotope signal and a strong correlation with past temperatures of the last 140 000 years based on other proxies however by comparing the dinocyst results to quantitative estimates of summer ssts based on diatoms radiolarians and foraminifer derived stable isotope records it can be shown that in several core intervals the dinocyst based summer ssts appeared to be extremely high in these intervals the dinocyst record seems to be highly influenced by selective degradation leading to unusual temperature ranges and to unrealistic palaeotemperatures we used the selective degradation index kt index to determine those intervals that have been biased by selective degradation in order to correct the palaeotemperature estimates we show that after correction the dinocyst based ssts correspond reasonably well with other palaeotemperature estimates for this region supporting the great potential of dinoflagellate cysts as a basis for quantitative palaeoenvironmental studies

multiproxy record of abrupt sea surface cooling across the eocene oligocene transition in the gulf of mexico the eocene oligocene transition eot ca 33 34 ma was a time of pronounced climatic change marked by the establishment of continental scale antarctic ice sheets the timing and extent of temperature change associated with the eot is controversial here we present multiproxy eot climate records 15 34 k y resolution from st stephens quarry alabama usa derived from foraminiferal mg ca d18o and tex86 we constrain sea surface temperatures ssts in the latest eocene and early oligocene and address the issue of climatic cooling during the eot paleotemperatures derived from planktic foraminifera mg ca and tex86 are remarkably consistent and indicate late eocene subtropical ssts of 28 c there was substantial and accelerated cooling of ssts 3 4 c through the latest eocene precursor d18o shift eot 1 prior to oligocene isotope 1 oi 1 our multispecies planktic foraminiferal d18o records diverge at the e o boundary 33 7 ma signifying enhanced seasonality in the earliest oligocene in the gulf of mexico

progressive cenozoic cooling and the demise of antarctica s last refugium the antarctic peninsula is considered to be the last region of antarctica to have been fully glaciated as a result of cenozoic climatic cooling as such it was likely the last refugium for plants and animals that had inhabited the continent since it separated from the gondwana supercontinent drill cores and seismic data acquired during two cruises shaldril i and ii in the northernmost peninsula region yield a record that when combined with existing data indicates progressive cooling and associated changes in terrestrial vegetation over the course of the past 37 million years mountain glaciation began in the latest eocene approximately 37 34 ma contemporaneous with glaciation elsewhere on the continent and a reduction in atmospheric co2 concentrations this climate cooling was accompanied by a decrease in diversity of the angiosperm dominated vegetation that inhabited the northern peninsula during the eocene a mosaic of southern beech and conifer dominated woodlands and tundra continued to occupy the region during the oligocene approximately 34 23 ma by the middle miocene approximately 16 11 6 ma localized pockets of limited tundra still existed at least until 12 8 ma the transition from temperate alpine glaciation to a dynamic polythermal ice sheet took place during the middle miocene the northernmost peninsula was overridden by an ice sheet in the early pliocene approximately 5 3 3 6 ma the long cooling history of the peninsula is consistent with the extended timescales of tectonic evolution of the antarctic margin involving the opening of ocean passageways and associated establishment of circumpolar circulation

oligocene climate dynamics a planktonic and benthic foraminiferal stable isotope stratigraphy of the oligocene equatorial pacific ocean drilling program site 1218 was generated at 6 kyr resolution between magnetochrons c9n and c11n 2n 26 4 30 ma on a newly developed astronomically calibrated timescale our data allow a detailed examination of oligocene paleoceanography the evolution of the early cryosphere and the influence of orbital forcing on glacioeustatic sea level variations spectral analysis reveals power and coherency for obliquity 40 kyr period and eccentricity 110 405 kyr orbital bands with an additional strong imprint of the eccentricity and 1 2 myr obliquity amplitude cycle driving ice sheet oscillations in the southern hemisphere planktonic and benthic foraminifera 18o are used to constrain the magnitude and timing of major fluctuations in ice volume and global sea level change glacial episodes related to obliquity and eccentricity variations occurred at 29 16 27 91 and 26 76 ma corresponding to glacioeustatic sea level fluctuations of 50 65 m alteration of high latitude temperatures and antarctic ice volume had a significant impact on the global carbon burial and equatorial productivity as cyclic variations are also recorded in the carbon isotope signal of planktonic and benthic foraminifera the water column carbon isotope gradient and estimated percent carbonate of bulk sediment we also investigate the implications of a close correspondence between oxygen and carbon isotope events and long term amplitude envelope extrema in astronomical calculations during the oligocene and develop a new naming scheme for stable isotope events on the basis of the 405 kyr eccentricity cycle count

planktonic foraminiferal turnover diversity fluctuations and geochemical signals across the eocene oligocene boundary in tanzania a major turnover in planktonic foraminifera occurred across the eocene oligocene e o boundary new drill holes through the e o boundary in southern tanzania contain extremely well preserved and diverse assemblages of planktonic foraminifera here we document a 1 2 million year record of assemblages diversity and stable isotope fluctuations through this critical interval which is often dissolved and or recrystallised in carbonate rich facies the e o boundary is marked by the abrupt extinction of all five remaining species of the family hantkeninidae and a distinct size reduction in the genus pseudohastigerina the boundary is preceded over a short stratigraphic interval by the extinction of turborotalia cerroazulensis turborotalia cocoaensis and turborotalia cunialensis quantitative analysis of planktonic foraminiferal assemblages reveals significant changes in the abundance of certain species and the composition of the assemblages we compare diversity fluctuations to the stable isotope record of pseudohastigerina naguewichiensis and use multispecies stable isotope analyses to determine the life habitats of the most important species a major shift in the evenness occurs at 33 8 ma associated with the extinction of the t cerroazulensis group suggesting acute ecological disturbance we propose that the extinction of the t cerroazulensis group at 33 8 ma was directly related to cooling of sea surface temperatures while the extinction of hantkeninidae was due to modifications in the thermal structure of the oceans and associated productivity changes after the extinctions renewed origination and diversification occurred leading to a characteristic oligocene planktonic foraminifer assemblage

early holocene temperature variability in the nordic seas the role of oceanic heat advection versus changes in orbital forcing received 7 january 2011 revised 15 july 2011 accepted 21 july 2011 published 22 october 2011 1 the separate roles of oceanic heat advection and orbital forcing on influencing early holocene temperature variability in the eastern nordic seas is investigated the effect of changing orbital forcing on the ocean temperatures is tested using the 1dice model and the 1dice results are compared with new and previously published temperature reconstructions from a transect of five cores located underneath the pathway of atlantic water from the faroe shetland channel in the south to the barents sea in the north the stronger early holocene summer insolation at high northern latitudes increased the summer mixed layer temperatures however ocean temperatures underneath the summer mixed layer did not increase significantly the absolute maximum in summer mixed layer temperatures occurred between 9 and 6 ka bp representing the holocene thermal maximum in the eastern nordic seas in contrast maximum in northward oceanic heat transport through the norwegian atlantic current occurred approximately 10 ka bp the maximum in oceanic heat transport at 10 ka bp occurred due to a major reorganization of the atlantic ocean circulation entailing strong and deep rejuvenation of the atlantic meridional overturning circulation combined with changes in the north atlantic gyre dynamic causing enhanced transport of heat and salt into the nordic seas

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

paleoceanographic reconstructions of surface ocean conditions in the greenland iceland and norwegian seas through the last 14 ka based on diatoms prior reconstructions of the last glacial maximum and the holocene did not include detailed paleoclimate data from the greenland iceland and norwegian gin seas which cover sensitive areas for oceanographic boundaries sea ice distribution and deep water formation in order to fill this gap we studied nine well dated sediment cores from this area and reconstructed the paleoceanographic conditions of the surface gin seas at 2000 year intervals since 13 400 bp based on the diatom record results show that a n s extending sea ice free corridor had opened along norway already at 13 400 bp indicating a northward flow of a branch of the north atlantic drift possibly caused by a change in the jet stream flow due to the decreased height of the north american ice sheet a major change of climatic conditions occurred over the gin seas as the insolation anomaly reached its maximum around 9000 bp when the sea ice cover and the oceanic fronts retreated to a northwesterly position along greenland and the ocean temperatures rose the first half of the holocene is recorded as the warmest period during the last 13 400 bp in the gin seas the duration of this climatic optimum decreased both toward the north and toward the margins of the area the second half of the holocene is characterized by a cooling trend in step with the decreasing insolation these results support the proposal of imbrie et al 1992 that the gin seas region acts as an initial responder to insolation changes