a cenozoic record of the equatorial pacific carbonate compensation depth atmospheric carbon dioxide concentrations and climate are regulated on geological timescales by the balance between carbon input from volcanic and metamorphic outgassing and its removal by weathering feedbacks these feedbacks involve the erosion of silicate rocks and organic carbon bearing rocks the integrated effect of these processes is reflected in the calcium carbonate compensation depth which is the oceanic depth at which calcium carbonate is dissolved here we present a carbonate accumulation record that covers the past 53 million years from a depth transect in the equatorial pacific ocean the carbonate compensation depth tracks long term ocean cooling deepening from 3 0 3 5 kilometres during the early cenozoic approximately 55 million years ago to 4 6 kilometres at present consistent with an overall cenozoic increase in weathering we find large superimposed fluctuations in carbonate compensation depth during the middle and late eocene using earth system models we identify changes in weathering and the mode of organic carbon delivery as two key processes to explain these large scale eocene fluctuations of the carbonate compensation depth

pacific ocean and cenozoic evolution of climate 1 the pacific ocean has played a major role in climate evolution throughout the cenozoic 65 0 ma it is a fundamental component of global heat transport and circulation the dominant locus of primary productivity and consequently the largest reservoir for carbon exchange between the oceans and the atmosphere a satisfactory understanding of the cenozoic evolutionary history of the pacific and its impact on global climate is currently data limited nevertheless the large dynamic range of cenozoic conditions sets the stage to greatly expand our understanding of global climate and biogeochemical cycles past earth experiments are particularly useful to understand interactions between climate and geosystems under different greenhouse gas loads we highlight in this review four important problems in which the pacific played a major role the effect of changing geographic boundary conditions on ocean circulation interactions between the carbon cycle and climate the pacific ocean s influence on north american climate and its water cycle and the gradual evolution of climate systems

paleoceanography of the east equatorial pacific over the past 16 myr and pacific atlantic comparison high resolution benthic foraminiferal δ18o and δ13c records at iodp site u1337 abstract we present astronomically tuned high resolution 3 4 kyr 15 8 myr long benthic foraminiferal 18 o and 13 c records from iodp site u1337 in the east equatorial pacific which provide a reference standard for stratigraphic correlation of deep sea sediments a long term glaciation history over the past 15 8 myr has been recorded in the 18 o two of the most significant glaciation events include the east antarctic ice sheet expansion eaie at 13 8 ma and the final onset of the northern hemisphere glaciation nhg in 3 3 2 5 ma a series of miocene and pliocene glaciation events exist between the eaie and nhg which are important glaciation attempts before the earth finally entered the full icehouse world in the late pleistocene a long term ocean carbon isotope decrease over the past 15 8 myr has been recorded in the 13 c ocean circulation change was the major cause of the ocean carbon isotope decrease in 9 4 8 1 ma and 4 0 ma whereas strengthened continental chemical weathering controlled the long term ocean carbon isotope decrease in most of the time of the past 15 8 myr the divergence in benthic foraminiferal 13 c and end provides strong evidence of significant ocean circulation change between 12 1 and 9 2 ma which was probably related to the formation of the isthmus of panama the internal feedbacks such as continental weathering and sea surface temperature change have great potential for modulating the weak 100 and 400 kyr signals in astronomical forcing into strong 100 and 400 kyr signals in global ice volume and carbon cycle

stratigraphic architecture of the cenozoic succession in the mcmurdo sound region antarctica an archive of polar palaeoenvironmental change in a failed rift setting the victoria land basin forms part of the failed west antarctic rift and preserves a cenozoic succession up to 4 km thick that records the onset of cenozoic glaciation and the history of antarctic glaciation over the past 34 myr this succession is relevant both to investigations of modern climate change and to studies of long term palaeoclimate change in general this study provides a sedimentological and stratigraphic review of the victoria land basin succession based on analysis of several continuous drillcores acquired since the 1970s and supported by seismic stratigraphic analysis of a large array of seismic reflection data an array of fifteen lithofacies is recognized within the victoria land basin cenozoic succession including fossiliferous and diversely bioturbated mudrocks and diatomites texturally mature sandstones and conglomerates mixed mudstones and sandstones with dispersed gravel with restricted bioturbation and diamictites and associated lithologies these facies record a variety of marine glaciomarine proglacial and subglacial environments locally volcanic and volcaniclastic deposits are interbedded in the succession lithofacies are arranged in repetitive vertical stacking patterns depositional sequences that record glacial advance retreat cycles with attendant relative sea level changes seven varieties of depositional sequences stratigraphic motifs are recognized within the succession as a whole and interpreted to record a range of depositional settings from rifts unaffected by glacial ice motif 7 through varying degrees of glacial influence with abundant meltwater contributions motifs 6 to 3 to cold polar glaciated environments such as that of today motifs 2 and 1 overall there is a gradual trend upward through the succession from motif 7 at the base towards motif 1 at the top but the trend is not monotonic a significant conclusion of this work is that a record of dynamic climate and glacial conditions is preserved through the entire 34 myr period of the cenozoic icehouse at least in the victoria land basin intervals characterized by consistent stratigraphic style motifs are recognized throughout the victoria land basin succession these intervals are of 1 to 6 myr duration each containing numerous depositional sequences they are one to two orders of magnitude longer than glacial interglacial cycles and record periods during which environmental conditions varied in an internally consistent manner these intervals are considered to reflect convolutions of orbital parameters that remained stable for periods of 106 a and then switched to alternative configurations such intervals are directly analogous to 1 to 8 myr intervals characterized by glaciogenic strata that are preserved within the late palaeozoic of eastern australia among other areas and may be a recurring stratigraphic response to icehouse climate regimes through geological time

stable isotope compositions of herbivore teeth indicate climatic stability leading into the mid miocene climatic optimum in idaho u s a abstract the effects of global climate change are manifested at the regional level consequently evaluation of links between palaeoenvironmental change and turnover of past biotas must use regional scale climate data here we test whether climate change influenced faunal and floral patterns leading up to and during the mid miocene climatic optimum mmco based on datasets collected in the railroad canyon section rcs central eastern idaho u s a specifically we use isotope compositions of herbivore tooth enamel to investigate how mean annual precipitation map mean annual temperature mat cold month mean temperature cmmt and temperature seasonality varied through the rcs and how this local record compares to global climate reconstructions isotope compositions of teeth from the fossil equid merychippus and rhinocerotid diceratherium were compared across five time bins from c 23 to c 15 ma bulk 18o values of both taxa indicate that meteoric water compositions were unchanged through the study interval consistently c 15 6 but were c 1 9 higher than current regional meteoric water this difference points to warmer climates in central eastern idaho during the miocene post middle miocene topographic uplift in western north america and or shifts to air mass trajectories serial sampling of enamel shows seasonal fluctuations in water compositions and temperature bulk 13c values indicate an average map of 190 range 10 510 mm yr 1 with no significant change through the study interval comparable to today s map 236 mm yr 1 the reconstructed semi arid seasonal warm climate for the rcs agrees with phytolith assemblage data from the same strata indicating dominantly open grassy habitats however it is inconsistent with previously held ideas of warm wet mid miocene climates in the northern rocky mountains nrm based on paleosol analyses our inferred stable climate conditions for the mmco of the nrm contrast with coeval records from europe and asia indicating sustained or enhanced warm and wet climates these differences point to a decoupling of regional climate from global trends and highlight the necessity of studying regional variation to understand the biotic impacts of global climate change

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

lithological correction of chemical weathering proxies based on k rb and mg contents for isolation of orbital signals in clastic sedimentary archives abstract the extraction of palaeoenvironmental palaeoclimatic signals from the chemical composition of siliciclastic sediments is valuable for the reconstruction of past environments particularly in continental basins here we test novel weathering proxies which are less sensitive to lithological control than the previously used raw element ratios k al k ti and k rb 1 local enrichment factors of k al mg al and k rb i e the element ratios corrected for grain size and matrix composition using local background functions al si fe and ca as explanatory variables and ordinary regression and 2 robust regression residuals of those element ratios based on isometric log ratio coordinates of the most relevant lithogenic elements ca fe rb si zr in the chemical composition chemical weathering proxies can be obtained from departures of chemical composition of sedimentary profiles from relationships with other chemical elements in particular those with grain size control the resulting weathering proxies were examined for the miocene deposits from the most basin the czech republic which recorded one of the major warm episodes of the cenozoic time the miocene climatic optimum the performance of weathering proxies has been checked by 1 comparison of individual proposed proxies in one drill core hk930 2 detailed analysis of orbital signals in the relevant compositional functions in hk930 and 3 lateral correlation of three cores hk930 du7 and do565 of the same basin the novel proxies show lateral stability and orbital signatures of short eccentricity obliquity and precession confirming their usefulness in palaeoenvironmental studies corrections for grain size and carbonate contents should help to isolate climatic content from the weathering proxies although in the studied sediments it weakened the precession component in the orbital signal as grain size proxies and other compositional data also carried orbital signals we propose to consider these proxy ideas in palaeoclimatic reconstructions based on chemical weathering proxies

the impact of hydrodynamics authigenesis and basin morphology on sediment accumulation in an upwelling environment the miocene monterey formation at shell beach and mussel rock pismo and santa maria basins central california u s a abstract in the sections at shell beach pismo basin and mussel rock santa maria basin both along the central california coast the miocene monterey formation is composed of laminated biosiliceous organic rich and phosphate rich sediments which are intercalated with carbonates and volcanogenic deposits the presence of small and large scale scours conglomerates gravity flow deposits slumps and condensed intervals reveals the importance of sediment reworking which is related to the presence of bottom currents the general morphology of the basins and recurrent high energy events of likely seismic origin the lithologies reflect strong upwelling enhanced primary productivity and the presence of an oxygen minimum zone which is indicated by ubiquitous lamination a general absence of bioturbation with the rare exception of traces related to the gravity flow displacement of trace makers high pyrite mo and u concentrations and molar ratios of total organic carbon and organic phosphorus toc p org of up to 2000 oxygen depletion was particularly severe during the early langhian and the late serravallian and early tortonian and favored the preservation of organic matter episodes of deposition of organic rich sediment were followed by longer phases of subdued sediment accumulation and early diagenetic phosphogenesis which resulted in the formation of a low porosity less permeable lid in the near surface sediments that assisted in preserving organic matter phosphogenesis occurred throughout the time interval considered approximately 17 5 6 5 ma and phosphate rich sediments formed especially during periods of sedimentary condensation in the langhian and earliest serravallian and the latest tortonian and early messinian a comparison of temporal trends in the type and quantity of deposited sediments between the two sections at shell beach and mussel rock and three sections of the santa barbara basin el capitan state beach naples beach and haskell beach confirms that towards the top of the monterey formation sediments become enriched in biosilica in all three basins the transition into this lithology occurred diachronously during the serravallian in the pismo and santa maria basins and tortonian in the santa barbara basin and was probably related to a diachronous shift to more intense upwelling in all three basins a phase of important condensation and phosphogenesis terminated monterey type sedimentation during the latest tortonian and early messinian in both the santa maria and santa barbara basins the uniform expression of this phase is interpreted as the result of improved connections between the two basins

the recycling of chromitites in ophiolites from southwestern north america abstract podiform chromitites occur in mantle peridotites of the late triassic puerto nuevo ophiolite baja california sur state mexico these are high cr chromitites cr cr cr al atomic ratio 0 61 0 69 that contain a range of minor and trace elements and show whole rock enrichment in ipge os ir ru that are similar to those of high cr ophiolitic chromitites crystallised from melts similar to high mg island arc tholeiites iat and boninites in supra subduction zone mantle wedges crystallisation of these chromitites from s undersaturated melts is consistent with the presence of abundant inclusions of platinum group minerals pgm such as laurite rus2 erlichmanite oss2 osmium and irarsite irass in chromite that yield tma trd model ages peaking at 325 ma thirty three xenocrystic zircons recovered from mineral concentrates of these chromitites yield ages 2263 44 ma to 278 4 ma and hf o compositions hf t 18 7 to 9 1 and 18o values

transient global cooling at the onset of early aptian oceanic anoxic event oae 1a the onset of the early aptian oceanic anoxic event oae 1a ca 120 ma coincided with a major perturbation of the carbon cycle which is reflected in the sedimentary carbon isotope record triggering mechanisms duration and climatic repercussions of this episode of accelerated organic matter burial remain poorly constrained here we present millennial scale bulk rock carbon and oxygen isotope data from a marly subtropical intrashelf basin la bedoule southeast france with unusually high sedimentation rates which track the onset of oae1a in unprecedented resolution our record reveals that the negative low amplitude delta 13 c excursion preceding oae1a lasted 100 k y implying that enhanced volcanic co 2 emission and or pulsed methane dissociation over a prolonged time span were instrumental in triggering oae1a the main positive carbon isotope shift at the onset of oae1a previously regarded as continuous occurred stepwise over an extended period of 300 k y transient climate cooling during the initial delta 13 c increase probably reflects ephemeral high latitude glaciation triggered by changes in radiative forcing and drawdown of atmospheric co 2

neogene evolution of the north eastern tibetan plateau based on sedimentary paleoclimatic and tectonic evidence abstract in this study the development of the north eastern tibetan plateau is investigated via an integrated study of the sedimentology magnetostratigraphy palaeogeography and cross section comparisons of the neogene sedimentary basins of the tibetan plateau from 23 to 17 ma this region was characterized by widespread angular unconformities and a sedimentary hiatus indicating the comprehensive uplift of the plateau the tectonic event that created the tibetan plateau triggered the evolution of sedimentary basins during the middle miocene climatic optimum event the growing qilian shan formed a barrier leading to cooler and drier conditions on the western side of the mountain however humid and warm conditions persisted on the eastern side of the range after this event this region was influenced by a global cooling trend and enhanced tectonic activity in the north eastern tibetan plateau at approximately 10 8 ma sedimentary data which were consistent with low temperature thermochronological records indicated the inversion of the surrounding mountains and rapid exhumation of the laji shan since 5 0 3 6 ma these intermontane basins gradually shrank and disappeared due to the overall uplift of the tibetan plateau and the accelerated global cooling trend and were associated with unconformities and growth strata that formed during stepwise north eastward thrusting tectonism

multiproxy reconstruction of the middle miocene požega palaeolake in the southern pannonian basin ne croatia prior to the badenian transgression of the central paratethys sea abstract the pannonian basin of croatia is the largest back arc extensional basin on the european continent located between the alps carpathians and dinarides syn rift subsidence started at 18 ma and predated the onset of the miocene climate optimum mco 17 14 7 ma in this paper we investigate the evolution of the fluvial lacustrine palaeoenvironment just prior to the transgression of the central paratethys sea studies are based on a 17 m thick section of the po ega palaeolake in the southern pannonian basin using palaeobiological mollusks ostracods palynomorphs fish otoliths mineralogical and sedimentological data our results reveal fluctuating freshwater and brackish conditions and a pulsating water budget which we relate to phases in which the basin was alternatively hydrologically open and closed we infer that the alternating environmental conditions can be best explained by dry and wet periods respectively droughts produced stagnant conditions algae overproduction and increased salinity levels supporting the survival of sporadically invading brackish water species the wet periods on the other hand led to lake highstand episodes expansion of lake area and to the widespread development of profundal facies the lake basin eventually became overfilled and connected through outflowing rivers with the central paratethys sea however the absence of brackish marine assemblages in the po ega palaeolake nevertheless indicates that there was no marine water inflow from the central paratethys at that time

orbitally paced phosphogenesis in mediterranean shallow marine carbonates during the middle miocene monterey event during the oligo miocene major phases of phosphogenesis occurred in the earth s oceans however most phosphate deposits represent condensed or allochthonous hemipelagic deposits formed by complex physical and chemical enrichment processes limiting their applicability for the study regarding the temporal pacing of miocene phosphogenesis the oligo miocene decontra section located on the maiella platform central apennines italy is a widely continuous carbonate succession deposited in a mostly middle to outer neritic setting of particular interest are the well winnowed grain to packstones of the middle miocene bryozoan limestone where occurrences of authigenic phosphate grains coincide with the prominent carbon isotope excursion of the monterey event this unique setting allows the analysis of orbital forcing on phosphogenesis within a bio chemo and cyclostratigraphically constrained age model la icp ms analyses revealed a significant enrichment of uranium in the studied authigenic phosphates compared to the surrounding carbonates allowing natural gamma radiation gr to be used as a qualitative proxy for autochthonous phosphate content time series analyses indicate a strong 405 kyr eccentricity forcing of gr in the bryozoan limestone these results link maxima in the gr record and thus phosphate content to orbitally paced increases in the burial of organic carbon particularly during the carbon isotope maxima of the monterey event thus phosphogenesis during the middle miocene in the mediterranean was controlled by the 405 kyr eccentricity and its influence on large scale paleoproductivity patterns rare earth element data were used as a tool to reconstruct the formation conditions of the investigated phosphates indicating generally oxic formation conditions which are consistent with microbially mediated phosphogenesis

minimal influence of recrystallization on middle miocene benthic foraminiferal stable isotope stratigraphy in the eastern equatorial pacific stable carbon and oxygen isotopes 13c and 18o of foraminiferal tests are amongst the most important tools in paleoceanography but the extent to which recrystallization can alter the isotopic composition of the tests is not well known here we compare three middle miocene 16 13 ma benthic foraminiferal stable isotope records from eastern equatorial pacific sites with different diagenetic histories to investigate the effect of recrystallization to test an extreme case we analyzed stable isotope compositions of benthic foraminifera from integrated ocean drilling program site u1336 for which the geochemistry of bulk carbonates and associated pore waters indicates continued diagenetic alteration in sediments 14 7 ma despite this diagenetic overprinting the amplitudes and absolute values of the analyzed u1336 stable isotopes agree well with high resolution records from better preserved sites u1337 and u1338 nearby our results suggest that although benthic foraminiferal tests of all three sites show some degree of textural changes due to recrystallization they have retained their original stable isotope signatures the good agreement of the benthic foraminiferal stable isotope records demonstrates that recrystallization occurred extremely rapidly 100 kyr after deposition this is confirmed by the preservation of orbital cyclicities in u1336 stable isotope data and 18o values being different to inorganic calcite that would precipitate from u1336 pore waters during late recrystallization the close similarity of the benthic foraminiferal stable isotope records between the sites allows the well resolved paleomagnetic results of site u1336 to be transferred to sites u1337 and u1338 improving the global geological timescale

variations in the strontium isotopic ratio of seawater during the miocene stratigraphic and geochemical implications a composite strontium isotopic seawater curve was constructed for the miocene between 24 and 6 ma by combining 87sr 86sr measurements of planktonic foraminifera from deep sea drilling project sites 289 and 588 site 289 with its virtually continuous sedimentary record and high sedimentation rates 26 m m y was used for constructing the oligocene to mid miocene part of the record which included the calibration of 63 biostratigraphic datums to the sr seawater curve using the timescale of cande and kent 1992 across the oligocene miocene boundary a brief plateau occurred in the sr seawater curve 87sr 86sr values averaged 0 70824 which is coincident with a carbon isotopic maximum cm o m from 24 3 to 22 6 ma during the early miocene the strontium isotopic curve was marked by a steep rise in 87sr 86sr that included a break in slope near 19 ma the rate of growth was about 60 ppm m y between 22 5 and 19 0 ma and increased to over 80 ppm m y between 19 0 and 16 ma beginning at 16 ma between carbon isotopic maxima cm3 and cm4 of woodruff and savin 1991 the rate of 87sr 86sr growth slowed and 87sr 86sr values were near constant from 15 to 13 ma after 13 ma growth in 87sr 86sr resumed and continued until 9 ma when the rate of 87sr 86sr growth decreased to zero once again the entire miocene seawater curve can be described by a high order function and the first derivative d87sr 86sr dt of this function reveals two periods of increased slope the greatest rate of 87sr 86sr change occurred during the early miocene between 20 and 16 ma and a smaller but distinct period of increased slope also occurred during the late miocene between 12 and 9 ma these periods of steepened slope coincide with major phases of uplift and denudation of the himalayan tibetan plateau region supporting previous interpretations that the primary control on seawater 87sr 86sr during the miocene was related to the collision of india and asia the rapid increase in 87sr 86sr values during the early miocene from 20 to 16 ma imply high rates of chemical weathering and dissolved riverine fluxes to the oceans in the absence of another source of co2 these high rates of chemical weathering should have quickly resulted in a drawdown of atmospheric co2 and climatic cooling through a reversed greenhouse effect the paleoclimatic record however indicates a warming trend during the early miocene culminating in a climatic optimum between 17 and 14 5 ma we suggest that the high rates of chemical erosion and warm temperatures during the climatic optimum were caused by an increase in the contribution of volcanic co2 from the eruption of the columbia river flood basalts crfb between 17 and 15 ma the decrease in the rate of crfb eruptions at 15 ma and the removal of atmospheric carbon dioxide by increased organic carbon burial in monterey deposits eventually led to cooling and increased glaciation between 14 5 and 13 ma the crfb hypothesis helps to explain the significant time lag between the onset of increased rates of organic carbon burial in the monterey at 17 5 ma as marked by increased 13c values and the climatic cooling and glaciation during the middle miocene as marked by the increase in 18o values which did not begin until 14 5 ma

t waves with long inland paths synthetic seismograms in order to provide more insight into land propagation of t phases signal analysis of these phases recorded inland has been carried out we found that the wave train is composed mainly of pg and sg waves which reach the seismic station from different azimuths with the hypothesis that the signal is the sum of discrete arrivals due to different rays crossing the continental slope at different locations synthetic seismograms of t waves are computed taking into account the variation of the conversion point along the slope the transmission of energy from the ocean to the continental crust is mainly due to diffraction effects the duration arid the amplitude of the t phase which are two criteria used to evaluate tsunami risk are greatly influenced by the shape of the continental slope

hydrologic cycling over antarctica during the middle miocene warming global warmth 20 15 million years ago allowed vegetation to grow on formerly ice covered areas of antarctica leaf wax and pollen data show that this growth was supported by increased hydrologic activity over the antarctic coast derived from a local moisture source

stable isotopes in large herbivore tooth enamel capture a mid miocene precipitation spike in the interior pacific northwest abstract stable carbon and oxygen isotopes of fossil ungulate tooth enamel were used to investigate the paleoclimate of the pacific northwest from the mid oligocene through pleistocene particularly targeting the mid miocene climatic optimum mmco we specifically test whether precipitation as inferred from tooth enamel 13c values relative to the 13c values of atmospheric co2 13c increased with increasing partial pressure of atmospheric co2 pco2 analysis emphasized water dependent equids rhinos and proboscideans but several artiodactyls and castor were also analyzed as available values of 13c 19 5 in the lower john day 27 and 18 ma and mascall 15 16 ma localities imply relatively high mean annual precipitation map ca 550 800 mm yr values of 13c

an astronomically dated record of earth s climate and its predictability over the last 66 million years much of our understanding of earth s past climate comes from the measurement of oxygen and carbon isotope variations in deep sea benthic foraminifera yet long intervals in existing records lack the temporal resolution and age control needed to thoroughly categorize climate states of the cenozoic era and to study their dynamics here we present a new highly resolved astronomically dated continuous composite of benthic foraminifer isotope records developed in our laboratories four climate states hothouse warmhouse coolhouse icehouse are identified on the basis of their distinctive response to astronomical forcing depending on greenhouse gas concentrations and polar ice sheet volume statistical analysis of the nonlinear behavior encoded in our record reveals the key role that polar ice volume plays in the predictability of cenozoic climate dynamics

obliquity forcing of organic matter accumulation during oceanic anoxic event 2 1 an analysis of orbitally influenced climate sensitive sedimentation is conducted across a meridional transect of the proto north atlantic to reconstruct the behavior of the carbon cycle and climate during oceanic anoxic event 2 oae 2 94 ma midlatitude to near equatorial sites spanning deep ocean to shelf environments are evaluated using a new inverse method for the identification and calibration of orbital influence in ancient strata the results yield consistent independent astrochronologies at each location compatible with the recently published radioisotopic astrochronologic time scale at the cenomanian turonian gssp and thus provide a unified high resolution temporal context for evaluation of the event the proto north atlantic astrochronologies document an amplification of obliquity power during oae 2 indicating that obliquity was the dominant pacemaker of organic matter accumulation by the latter portion of the event the strong obliquity signal suggests an influence of high latitude climate processes across midlatitude deep ocean to tropical shelf environments changes in oceanic circulation during oae 2 represent a likely mechanism for the propagation of a high latitude signal and proxy data from demerara rise reveal the development of a new intermediate water mass source synchronous with the record of obliquity amplification we hypothesize that a dense high latitude water mass displaced a pre existing nutrient rich anoxic deep water layer in the proto north atlantic augmented by enhanced volcanism driving an episode of high productivity that lasted 700 800 ka the development and intensification of the new intermediate deep water source was potentially driven by eustatic sea level rise which created expansive seaways in mid to high latitudes

the role of the global carbonate cycle in the regulation and evolution of the earth system we review one of the most ancient of all the global biogeochemical cycles and one which reflects the profound geochemical and biological changes that have occurred as the earth system has evolved through time that of calcium carbonate caco3 in particular we highlight a mid mesozoic revolution in the nature and location of carbonate deposition in the marine environment driven by the ecological success of calcareous plankton this drove the creation of a responsive deep sea sedimentary sink of caco3 the result is that biologically driven carbonate deposition provides a significant buffering of ocean chemistry and of atmospheric co2 in the modern system however the same calcifying organisms that under pin the deep sea carbonate sink are now threatened by the continued atmospheric release of fossil fuel co2 and increasing acidity of the surface ocean we are not yet in a position to predict what the impact on caco3 production will be or how the uptake of fossil fuel co2 by the ocean will be affected this uncertainty in the future trajectory of atmospheric co2 that comes from incomplete understanding of the marine carbonate cycle is cause for concern

magneto biostratigraphy and paleoenvironments of the miocene freshwater sediments of the sarajevo zenica basin abstract the sarajevo zenica basin of bosnia herzegovina was part of the dinaride lake system a large network of miocene long lived freshwater basins in southeastern europe the basin contains a thick sedimentary succession of carbonates coals and mixed siliciclastic deposits that reflects the paleoclimatic and tectonic evolution of the region in this study we present novel integrated magneto bio stratigraphic and sedimentological data and reconstruct the paleoenvironmental evolution of the sarajevo zenica basin during its two main evolutionary phases thrusting and extension the basal oligo miocene freshwater paleoenvironments are characterized by alternating palustrine shallow lacustrine and distal fluvial phases the base level fluctuations are largely controlled by syn sedimentary pulses of tectonic loading during the final phase of thrusting in the internal dinarides the majority of this succession is considered early miocene in age which contrasts with previous oligocene age estimates the subsequent extensional phase initiated not later than 18 4 ma this coarsening upward sequence of lacustrine carbonates silts sands and conglomerates is correlated between 17 2 and 15 ma c5cr c5br by means of integrated bio magnetostratigraphy during this upper extensional phase subsidence and sediment influx was generally controlled by activity along the basin bounding normal fault overruling smaller scale climatic influences we conclude that the existence of the long lived sarajevo lake is coeval with other dinaric and southern pannonian lakes and overlaps in time with the miocene climatic optimum sedimentation in the sarajevo zenica basin terminated at 15 14 ma which concurs with both the end of the climatic optimum as well as the cessation of extension in the dinarides these results will help to better quantify the paleoclimatic changes in the dinaride lake system as well as the regional tectono sedimentary events such as potential migrations of deformation across the dinarides

depletion of 13c in cretaceous marine organic matter source diagenetic or environmental sigal geochemical studies of cretaceous strata rich in organic carbon oc from deep sea drilling project dsdp sites and several land sections reveal several consistent relationships among amount of oc hydrocarbon generating potential of kerogen measured by pyrolysis as the hydrogen index hi and the isotopic composition of the oc first there is a positive correlation between hi and oc in strata that contain more than about 1 oc second percent oc and hi often are negatively correlated with carbon isotopic composition 13c of kerogen the relationship between hi and oc indicates that as the amount of organic matter increases this organic matter tends to be more lipid rich reflecting the marine source of the organic matter cretaceous samples that contain predominantly marine organic matter tend to be isotopically lighter than those that contain predominantly terrestrial organic matter average 13c values for organic matter from most cretaceous sites are between 26 and 28 and values heavier than about 25 occur at very few sites most of the 13c values of miocene to holocene oc rich strata and modern marine plankton are between 16 to 23 values of 13c of modern terrestrial organic matter are mostly between 23 and 33 the depletion of terrestial oc in 13c relative to marine planktonic oc is the basis for numerous statements in the literature that isotopically light cretaceous organic matter is of terrestrial origin even though other organic geochemical and or optical indicators show that the organic matter is mainly of marine origin a difference of about 5 in 13c between modern and cretaceous oc rich marine strata suggests either that cretaceous marine planktonic organic matter had the same isotopic signature as modern marine plankton and that signature has been changed by diagenesis or that oc derived from cretaceous marine plankton was isotopically lighter by about 5 relative to modern plankton oc diagenesis does not produce a significant shift in 13c in miocene to holocene sediments and therefore probably did not produce the isotopically light cretaceous oc this means that cretaceous marine plankton must have had 13c values that were about 5 lighter than modern marine plankton and at least several per mil lighter than cretaceous terrestrial vegetation the reason for these lighter values however is not obvious it has been proposed that concentrations of co2 were higher during the middle cretaceous and this more available co2 may be responsible for the lighter 13c values of cretaceous marine organic matter

the middle miocene climatic transition east antarctic ice sheet development deep ocean circulation and global carbon cycling abstract the middle miocene represents a major change in state in cenozoic climatic evolution following the climax of neogene warmth in the late early miocene at 16 ma the early stage of this climatic transition from 16 to 14 8 ma was marked by major short term variations in global climates east antarctic ice sheet eais volume sea level and deep ocean circulation in the later stage from 14 8 to 12 9 ma climatic developments included major growth of the eais and associated antarctic cooling a distinct increase in the meridional temperature gradient large fluctuations in sea level followed by a global sea level fall and important changes in deep water circulation including increased production of southern component water east antarctic ice sheet growth and polar cooling also had large effects on global carbon cycling and on the terrestrial biosphere including aridification of mid latitude continental regions increased stability of the eais after 14 8 ma represents a crucial step in the establishment of late neogene global climate systems what controlled these changes in polar climates and the east antarctic ice sheet deep ocean circulation changes probably played a major role in the evolution and variation in polar climates as they have throughout the cenozoic oxygen and carbon isotopic evidence for warm saline deep water production in the eastern tethyan northern indian ocean indicates that meridional heat transport to the antarctic inhibited cenozoic polar cooling and eais growth during the early middle miocene from 16 to 14 8 ma inferred competition between warm low latitude sources derived from the eastern tethyan northern indian ocean and a cold high latitude source southern component water from 16 to 14 8 ma may have been associated with instability in the antarctic climate and cryosphere reduction of warm saline deep water flow to the southern ocean at 14 8 ma may have decreased meridional heat transport to the antarctic cooling the region and leading to increased production of southern component water these middle miocene climatic and cryospheric changes in the antarctic had profound effects on marine and terrestrial climates as the meridional surface temperature gradient increased boundaries between climatic zones strengthened leading to increased aridification of mid latitude continental regions in australia africa and north and south america enhancing the development of grasslands and stimulating the evolution of grazing mammals

biogenic sediment regimes in the neogene equatorial pacific iodp site u1338 burial production and diatom community abstract the equatorial pacific experienced significant changes in productivity and microfossil assemblage since 16 million years ago ma we compiled a record of those changes from iodp site u1338 using a reconnaissance of diatom assemblages and high resolution xrf scan chemical profiles 1 2 kyr spacing productivity and caco3 dissolution intervals are defined by sediment component ratios in particular opal clay opal baso4 and caco3 baso4 or caco3 clay there are large abrupt changes in export production in the miocene especially compared to the pleistocene and pliocene and average levels of export production are higher throughout the miocene compared to the pliocene and pleistocene using diatom assemblages and bulk sediment composition the u1338 sediment record is divided into several distinct deposition regimes 1 a middle miocene regime 13 2 ma marked by low diatom numbers and a few short lived productivity intervals 2 a carbonate crash regime distinguished by an older substage 13 2 10 2 ma with relatively high abundances of productivity related diatoms and common productivity related depositional intervals interspersed with caco3 dissolution intervals and a younger carbonate crash substage 10 2 8 0 ma with weaker brief productivity intervals high caco3 dissolution and moderately high numbers of upwelling diatom species 3 the biogenic bloom regime 8 0 4 5 ma marked by extended periods of high opal and caco3 deposition with a maximum between 7 0 and 6 4 ma and 4 a pliocene modern regime 4 5 0 ma with lower productivity and high cyclic caco3 dissolution changes in production and dissolution result from reorganizations of nutrient supply to the equatorial pacific not by higher wind driven upwelling we propose that nutrients were more accessible in the miocene because of a combination of factors including higher organic matter degradation in the upper water column and deep intermediate nutrient pathways that efficiently recycled nutrients to upwelling zones closure of the central american seaway was likely a prime cause of the biogenic bloom

seawater paleotemperature and paleosalinity evolution in neritic environments of the mediterranean margin insights from isotope analysis of bivalve shells the first step of ice sheet build up on antarctica at the eocene oligocene boundary was followed by a phase of climate instability culminating during the miocene with a warming event called the middle miocene climate optimum mmco that ended with a marked cooling phase identified as the middle miocene climate transition mmct while numerous benthic foraminifera 18o and mg ca data have been used to capture the global climate evolution during this interval of climate and ice sheet instability geochemical records from shallow water carbonates still remain scarce yet such records are crucial to capture the diversity of regional environmental responses to global climate changes and thus to better understand the behavior of our climate system during this critical interval in this work we test the potential of a multi proxy approach 18o clumped isotope 47 strontium isotopes 87sr 86sr applied to bivalves recovered from the liguro provencal basin and rhodano provencal basin northwestern of the mediterranean sea to reconstruct the evolution of shallow seawater temperature and salinity in this region over the latest oligocene to middle miocene interval 10 myrs our results highlight a local cooling in the northwestern mediterranean sea during the mmco that contrasts with the warming observed in other regions with seawater temperatures inferred from 47 analyses in the 13 18 c range these cool seawater temperatures recorded in the studied region during the mmco are much cooler than those recorded in the open oceans but are in agreement with the proliferation of bryozoan observed in the castillon du gard area during this interval low bivalve 18o values 3 24 in average are recorded during this episode are interpreted to reflect enhanced freshwater inputs lowering local salinity and seawater 18o such enhanced freshwater inputs point to a phase of enhanced hydrological cycle in the studied region possibly linked to the global mid miocene warming event bivalve 87sr 86sr data mostly fall within the global seawater sr isotope reference curve but remain compatible with enhanced freshwater inputs during the aquitanian and during the langhian as these inputs were probably not important enough to induce a large departure from the seawater curve at a regional scale

orbital forcing and abrupt events in a continental weathering proxy from central europe most basin czech republic 17 7 15 9 ma recorded beginning of the miocene climatic optimum abstract we describe orbital forcing in siliciclastic lacustrine sediments deposited in central europe ca 50 5 n and 13 5 e the most basin the czech republic between 17 7 and 15 9 ma i e before the miocene climatic optimum mco and in its early stage chemical element analysis combined with magneto and cyclostratigraphy produced a consistent stratigraphy for the studied basin fill the palaeoenvironmental record is mainly based on variations of the chemical weathering intensity in the lake catchment normalised potassium concentration k al or k ti the most basin sedimentary profile is specific by relatively high deposition rates typically 20 cm kyr sampling density corresponded to temporal resolution of 1 2 kyr and sensitivity to a regional continental climate for age control we used the atnts2012 for younger sediments and an alternative age of the onset of c5dn chron and the end of c5dr 1r short chron in the earliest studied interval the chemical weathering intensity in the catchment was controlled by precession while between 17 5 and 17 15 ma short eccentricity was mainly driving chemical weathering intensity after 17 05 ma i e just before the onset of the mco and in the period of persistent high eccentricity between 16 95 and 16 7 ma chemical weathering intensity reached its precession controlled maxima in the subsequent period of the persistent low eccentricity at 16 65 ma the orbital signal nearly vanished in the most basin abrupt but temporary environmental change occurred in the interval between 16 5 and 16 35 ma polarity chron c5cn 2n within two cycles of high eccentricity its trigger is uncertain but it might have been local or regional the obtained composite record was compared with marine 13c and 18o data showing certain global control of the most basin deposits the most basin record thus shows climatic events of the pre mco and early mco period in terrestrial settings of central europe with changes at 17 05 16 65 and 16 5 ma possibly representing triggers of the mco

reconstruction of oceanic circulation patterns in the tropical pacific across the early middle miocene boundary as inferred from radiolarian assemblages abstract although there have been attempts to infer neogene oceanic circulation patterns in the tropical pacific on the basis of multiple marine proxies oceanic circulation patterns across the early middle miocene boundary are still poorly understood despite paleoclimate having significantly changed during this interval in this study we reconstruct the changes in tropical oceanic circulation patterns in the pacific across the early middle miocene boundary based on radiolarian assemblages obtained at integrated ocean drilling program site u1335 in the eastern tropical pacific the radiolarian upwelling taxa increased during four intervals 18 4 18 1 ma 16 9 15 7 ma 15 2 14 6 ma 14 2 13 4 ma radiolarian temperature index rti was calculated using the relative abundances of the warm water cluster b1 and cool water taxa cluster b2 in order to evaluate relative temperature fluctuations of the surface water the sea surface temperature index was relatively high from 16 8 to 16 0 ma and gradually decreased from 16 0 to 14 6 ma subsequently the temperature index decreased stepwise at 13 9 and 13 4 ma and became relatively low from 13 4 to 12 7 ma comparison of the rti record in the eastern tropical pacific to the climatic index based on the benthic foraminiferal 18o record shows that variability in the two records follows a roughly similar trend from the early to the middle miocene however the sea surface temperature record does not indicate a sharp increase in warmth in the eastern tropical pacific during the mid miocene climatic optimum 1 mmco 1 as suggested by the benthic isotopic record this is likely because of increased upwelling of cool nutrient rich water at this time beginning in the latest early miocene 17 ma radiolarian assemblages were dominated by different taxa in the eastern and western tropical pacific this pattern is interpreted as indicating a shallower thermocline in the east and a deeper thermocline in the west based on the relative abundance of the upwelling taxa there is an overall increasing trend in this difference since the latest early miocene we tie these events to the effective closure of the indo pacific seaway and the development of a substantial western pacific warm pool along with the development of a strong equatorial undercurrent

the evolution of pco2 ice volume and climate during the middle miocene abstract the middle miocene climatic optimum 17 15 ma mco is a period of global warmth and relatively high co2 and is thought to be associated with a significant retreat of the antarctic ice sheet ais we present here a new planktic foraminiferal 11b record from 16 6 to 11 8 ma from two deep ocean sites currently in equilibrium with the atmosphere with respect to co2 these new data demonstrate that the evolution of global climate during the middle miocene as reflected by changes in the cyrosphere was well correlated to variations in the concentration of atmospheric co2 what is more within our sampling resolution 1 sample per 300 kyr there is no evidence of hysteresis in the response of ice volume to co2 forcing during the middle miocene contrary to what is understood about the antarctic ice sheet from ice sheet modelling studies in agreement with previous data we show that absolute levels of co2 during the mco were relatively modest 350 400 ppm and levels either side of the mco are similar or lower than the pre industrial 200 260 ppm these new data imply the presence of either a very dynamic ais at relatively low co2 during the middle miocene or the advance and retreat of significant northern hemisphere ice recent drilling on the antarctic margin and shore based studies indicate significant retreat and advance beyond the modern limits of the ais did occur during the middle miocene but the complete loss of the ais was unlikely consequently it seems that ice volume and climate variations during the middle miocene probably involved a more dynamic ais than the modern but also some component of land based ice in the northern hemisphere

mid miocene paleoproductivity in the atlantic ocean and implications for the global carbon cycle 1 a prominent middle miocene 17 5 13 5 ma carbon isotope excursion ubiquitously recorded in carbonate sediments has been attributed to enhanced marine productivity and sequestration of 13c depleted organic carbon in marine sediments or enhanced carbon burial in peat lignite deposits on land here we test the hypothesis that the marine 13c record reflects a change in productivity with proxy records from three atlantic ocean sites deep sea drilling program site 608 and ocean drilling program sites 925 and 1265 our multiproxy approach is based on benthic foraminiferal accumulation rates elemental ratios ba al and p al the 13c of bulk sedimentary organic matter and dissolution indices we compare these proxies to benthic foraminiferal 13c values measured on the same samples our results indicate that marine paleoproductivity in the atlantic ocean is not related to the benthic foraminiferal 13c excursion a numerical box model confirms that marine productivity cannot account for the 13c maximum the model shows that sequestration of 1 5 1018 mol c in the terrestrial realm over a period of 3 ma leads to a 0 9 13c increase in the deep ocean which is near the observed records therefore an increase in continental organic carbon sequestration is the most plausible way to enrich the ocean s carbon pool with 13c which is consistent with coeval lignite deposits worldwide the 13c values of bulk sedimentary organic matter parallel the 13c of dissolved inorganic carbon as reflected by benthic foraminiferal 13c values suggesting no significant change in atmospheric pco2 levels over the investigated period

geochemistry and isotopic study of southern bay of bengal sediments implications for provenance and paleoenvironment during the middle miocene abstract the bay of bengal bob the largest bay in the world is known to receive large amounts of fresh water and suspended particulate matter from different sources the sediments deposited in the bay serve as a repository for paleoenviromental reconstruction studies the miocene epoch is an important interval in geologic time as it is marked by major climatic events that controlled ocean productivity redox conditions and provenance of sediments however limited work has been carried out to establish paleoenviromental changes and provenance of sediments during the miocene here we present detailed geochemical and radiogenic sr nd isotopic results from predominantly middle miocene sediments of ocean drilling program odp site 758a located in the southern bob lat 5 23 n long 90 21 e water depth 2925 m to understand paleoredox conditions paleoproductivity and provenance the results suggest that these sediments are strongly linked to climatically modulated surface processes that affected the region the distribution of redox sensitive element proxies u v cr at interval 17 8 ma points to an oxic depositional environment the major trace and rare earth elements distribution supports prevalence of the indian summer monsoon ism at 12 10 ma productivity proxies babio porg show a decreasing trend during colder events east antarctic ice sheet expansion eais and advent of late miocene cooling lmc events the trace and rare earth element concentrations are generally low except at intervals where glass shards were found the 87sr 86sr and end 0 values indicate that the sediments belong to the high himalayan sedimentary series hhss throughout the middle miocene however prior to initiation of the ism these sediments underwent meteoric alteration in the lowlands before deposition in the bob our records suggest that sediments at odp site 758a may have been introduced into the bob through the irrawaddy yarlung tsangpo drainage system during the entire period of this study the irrawaddy yarlung tsangpo system drained the indus tsangpo suture zone southern tibet the eastern himalayas and the arakan coast before debouching in the bob

mid miocene isotope stratigraphy in the deep sea high resolution correlations paleoclimatic cycles and sediment preservation mid miocene pelagic sedimentary sections can be correlated using intermediate and high resolution oxygen and carbon isotopic records of benthic foraminifera precision of a few tens of thousands of years is readily achievable at sites with high sedimentation rates for example deep sea drilling project sites 289 and 574 the mid miocene carbon isotope records are characterized by an interval of high 13c values between 17 and 13 5 ma the monterey excursion of vincent and berger 1985 upon which are superimposed a series of periodic or quasi periodic fluctuations in 13c values these fluctuations have a period of approximately 440 kyr suggestive of the 413 kyr cycle predicted by milankovitch theory vincent and berger proposed that the monterey excursion was the result of increased organic carbon burial in continental margins sediments the increased 13c values called 13c maxima superimposed on the generally high mid miocene signal coincide with increases in 18o values suggesting that periods of cooling and or ice buildup were associated with exceptionally rapid burial of organic carbon and lowered atmospheric co2 levels it is likely that during the monterey excursion the ocean atmosphere system became progressively more sensitive to small changes in insolation ultimately leading to major cooling of deep water and expansion of continental ice we have assigned an absolute chronology based on biostratigraphic and magneto biostratigraphic datum levels to the isotope stratigraphy and have used that chronology to correlate unconformities seismic reflectors carbonate minima and dissolution intervals intervals of sediment containing 13c maxima are usually better preserved than the overlying and underlying sediments indicating that the 13c values of tco2 in deep water and the corrosiveness of seawater are inversely correlated this again suggests that the 13c maxima were associated with rapid burial of organic carbon and reduced levels of atmospheric co2 the absolute chronology we have assigned to the isotopic record indicates that the major mid miocene deepwater cooling ice volume expansion took 2 m y and was not abrupt as had been reported previously the cooling appears abrupt at many sites because the interval is characterized by a number of dissolution intervals the cooling was not monotonic and the 2 m y interval included an episode of especially rapid cooling as well as a brief return to warmer conditions before the final phase of the cooling period the increase in 18o values of benthic foraminifera between 14 9 and 12 9 ma was greatest at deeper water sites and at sites closest to antarctica the data suggest that the 18o value of seawater increased by no more than about 1 1 per mil during this interval and that the remainder of the change in benthic 18o values resulted from cooling in antarctic regions of deepwater formation equatorial planktonic foraminifera from sites 237 and 289 exhibit a series of 0 4 per mil steplike increases in 13c values only one of these increases in planktonic 13c is correlated with any of the features in the mid miocene benthic carbon isotope record

middle to late miocene stepwise climate cooling evidence from a high resolution deep water isotope curve spanning 8 million years 1 we present high resolution 2 3 kyr benthic foraminiferal stable isotopes in a continuous well preserved sedimentary archive from the west pacific ocean ocean drilling program site 1146 which track climate evolution in unprecedented resolution over the period 12 9 to 8 4 ma we developed an astronomically tuned chronology over this interval and integrated our new records with published isotope data from the same location to reconstruct long term climate and ocean circulation development between 16 4 and 8 4 ma this extended perspective reveals that the long eccentricity 400 kyr cycle is prominently encoded in the 13c signal over most of the record reflecting long term fluctuations in the carbon cycle the 18o signal closely follows variations in short eccentricity 100 kyr and obliquity 41 kyr in particular the obliquity cycle is prominent from 14 6 to 14 1 ma and from 9 8 to 9 2 ma when high amplitude variability in obliquity is congruent with low amplitude variability in short eccentricity the 18o curve is additionally characterized by a series of incremental steps at 14 6 13 9 13 1 10 6 9 9 and 9 0 ma which we attribute to progressive deep water cooling and or glaciation episodes following the end of the miocene climatic optimum on the basis of 18o amplitudes we find that climate variability decreased substantially after 13 ma except for a remarkable warming episode at 10 8 10 7 ma at peak insolation during eccentricity maxima 100 and 400 kyr this transient warming associated with a massive negative carbon isotope shift is reminiscent of intense global warming events at eccentricity maxima during the miocene climatic optimum

eastern equatorial pacific benthic foraminiferal distribution and deep water temperature changes during the early to middle miocene abstract we investigate changes in benthic foraminiferal assemblages and estimate bottom water temperatures bwt based on mg ca ratios of oridorsalis umbonatus over three selected intervals of major climate change during the late early to middle miocene at integrated ocean drilling program iodp sites u1337 4463 m water depth and u1338 4200 m water depth eastern equatorial pacific ocean the targeted intervals are 1 the onset of the miocene climatic optimum mco at 16 9 ma and associated carbon cycle perturbation site u1337 2 the episode of peak warmth within the mco centered at 15 6 ma site u1338 3 the major cooling step at 13 8 ma related to east antarctic ice sheet expansion site u1338 assemblages from these three intervals are mainly composed of cosmopolitan long ranging e g paleogene to recent lower bathyal to abyssal species including calcareous elongated forms that became extinct during the middle pleistocene the onset of the mco and interval of peak warmth had little impact on benthic foraminiferal accumulation rates bfar abundances and assemblage composition a transient bwt warming of 2 6 c at the onset of the interval of peak warmth concurred with a benthic stable oxygen isotope 18 o decrease of 1 suggesting that the 18 o decrease was largely controlled by bwt changes a substantial increase in bfar and in the abundances of epistominella exigua and epifaunal taxa after 13 83 ma coincides with increased opal accumulation rates reflecting enhanced and seasonally pulsed organic carbon c org flux to the seafloor during the global cooling step during this interval bwt decrease by 1 7 c concurrent with a 1 0 increase in the stable oxygen isotope composition of seawater 18 o sw comparable trends at ocean drilling program odp site 1146 in the south china sea with a 2 2 c cooling and 0 9 increase in 18 o sw at 13 8 ma further support that the benthic 18 o increase during the major cooling step was largely controlled by ice volume changes

equatorial pacific productivity changes near the eocene oligocene boundary there is general agreement that productivity in high latitudes increased in the late eocene and remained high in the early oligocene evidence for both increased and decreased productivity across the eocene oligocene transition eot in the tropics has been presented usually based on only one paleoproductivity proxy and often in sites with incomplete recovery of the eot itself a complete record of the eocene oligocene transition was obtained at three drill sites in the eastern equatorial pacific ocean odp site 1218 and iodp sites u1333 and u1334 four paleoproductivity proxies that have been examined at these sites together with carbon and oxygen isotope measurements on early oligocene planktonic foraminifera give evidence of ecologic and oceanographic change across this climatically important boundary export productivity dropped sharply in the basal oligocene 33 7 ma and only recovered several hundred thousand years later however overall paleoproductivity in the early oligocene never reached the average levels found in the late eocene and in more modern times changes in the isotopic gradients between deep and shallow living planktonic foraminifera suggest a gradual shoaling of the thermocline through the early oligocene that on average affected accumulation rates of barite benthic foraminifera and opal as well as diatom abundance near 33 5 ma an interval with abundant large diatoms beginning at 33 3 ma suggests an intermediate thermocline depth which was followed by further shoaling a dominance of smaller diatoms and an increase in average primary productivity as estimated from accumulation rates of benthic foraminifera

closing an early miocene astronomical gap with southern ocean δ18o and δ13c records implications for sea level change we present orbital scale resolution 10 kyr benthic foraminiferal 18o and 13c records from the kerguelen plateau ocean drilling program odp sites 751 and 747 from 14 5 20 0 ma spanning the miocene climate optimum mco 15 17 ma our records fill a critical gap from 17 18 ma a time when many other deep sea records are affected by dissolution we tested the fidelity of published magneto biostratigraphic age models for these sites by astronomically tuning to the 405 kyr eccentricity cycle a comparison of spectral estimates between the untuned and tuned records as well as coherency with laskar s 2004 eccentricity solution revealed quasi 100 kyr cyclicity in 18o and 13c there is only a weak signal associated with the 41 kyr obliquity cycle likely due to the 10 kyr sampling limiting resolution the 18o variations point to persistent 405 and quasi 100 kyr modulations of temperature and sea level changes through the early to middle miocene as predicted by astronomical solutions with changing dominance of the 100 and 41 kyr beat comparison of 18o records with early to middle miocene sequences from the new jersey shelf northeast australian margin bahamas and maldives suggests that the dominant sea level period preserved is the 1 2 myr obliquity cycle with sequence boundaries associated with 18o increases or maxima on the new jersey margin higher order sequences reflect the quasi 100 kyr eccentricity cycles as modulated by 405 kyr cycles we suggest that nesting of stratigraphic cycles is a function of 1 pervasive though changing milankovitch forcing of global mean sea level change and 2 preservation that depends on sufficient sediment supply and accommodation

onset of the mid cretaceous greenhouse in the barremian aptian igneous events and the biological sedimentary and geochemical responses basalts and biostratigraphy dated at 125 120 ma from the ontong java and manihiki plateaus in the western pacific evidence the largest volcanic event in earth history in at least the past 160 m y the intervening nova canton trough rifted at about 121 118 ma and a number of guyots and seamounts formed concurrently or slightly later geological events that probably were responses to these volcanic tectonic events occurred in the following chronostratigraphic order biotic fluctuations began at about 122 5 ma at about 122 0 ma 87sr 86sr began to decline slowly metal concentrations of co mn pb yb and cu in sediments peaked at about 121 5 121 2 ma changes in planktonic communities and sedimentation culminated in a nannoconid crisis just prior to 120 5 ma and in the selli black shale oae la at about 120 5 119 5 ma a sharp drop in 13c occurred at the beginning of the selli event and rebounded into a longer positive excursion that reached a peak after the selli event at about 119 5 118 5 ma at 120 5 ma 87sr 86sr declined rapidly and reached a minimum at about 116 113 ma we speculate that the intensity of these latter responses suggests a corresponding peak in volcanic tectonic activity at about 121 119 ma

eccentricity pacing of eastern equatorial pacific carbonate dissolution cycles during the miocene climatic optimum the miocene climatic optimum mco similar to 16 9 to 14 7ma provides an outstanding opportunity to investigate climate carbon cycle dynamics during a geologically recent interval of global warmth we present benthic stable oxygen o 18 and carbon c 13 isotope records 5 12kyr time resolution spanning the late early to middle miocene interval 18 to 13ma at integrated ocean drilling program iodp site u1335 eastern equatorial pacific ocean the u1335 stable isotope series track the onset and development of the mco as well as the transitional climatic phase culminating with global cooling and expansion of the east antarctic ice sheet at similar to 13 8ma we integrate these new data with published stable isotope geomagnetic polarity and x ray fluorescence xrf scanner derived carbonate records from iodp sites u1335 u1336 u1337 and u1338 on a consistent astronomically tuned timescale benthic isotope and xrf scanner derived caco3 records depict prominent 100kyr variability with 400kyr cyclicity additionally imprinted on c 13 and caco3 records pointing to a tight coupling between the marine carbon cycle and climate variations our intersite comparison further indicates that the lysocline behaved in highly dynamic manner throughout the mco with 75 carbonate loss occurring at paleodepths ranging from similar to 3 4 to similar to 4km in the eastern equatorial pacific ocean carbonate dissolution maxima coincide with warm phases o 18 minima and c 13 decreases implying that climate carbon cycle feedbacks fundamentally differed from the late pleistocene glacial interglacial pattern where dissolution maxima correspond to c 13 maxima and o 18 minima carbonate dissolution cycles during the mco were thus more similar to paleogene hyperthermal patterns

controls on neogene carbonate facies and stratigraphic architecture of an isolated carbonate platform the caribbean island of bonaire abstract the neogene carbonate succession on the island of bonaire netherland antilles shows complex geometries associated with a sequence of depositional and erosional events which reflects the history of this isolated platform and the interaction between eustasy and tectonics three major episodes of carbonate platform deposition are defined which show contrasting depositional styles 1 aggradational platform lower middle miocene with sediments showing a fining upward trend from mixed coral rudstone to medium grained coralgal grain packstone partly dolomitized and tilted by tectonic deformation 2 progradational platform upper miocene pliocene which is formed of several shallowing upward prograding units mainly composed of reworked red algal grain packstone with significant dolomitization passing upward to shoreline and aeolian deposits formed of cor algal grain packstone and large benthic foraminifera grainstone and 3 flat topped platform pleistocene with a reefal framework composed of a rich variety of corals in a bioclastic pack wackestone matrix these platform episodes exhibit contrasting stacking patterns and are separated by erosional unconformities overprinting this depositional succession is a series of quaternary near horizontal shoreline erosional terraces and vertical cliffs which have been cut into the island stratigraphy and complicate the stratal field relationships however this terrace morphology clearly does not represent depositional episodes as has been suggested before the internal architecture of each of the three carbonate platform reflects of the dynamics of sedimentation with allogenic controls the latter relate to major oceanographic and tectonic events in the region including changing ocean circulation as a result of the closure of the panama isthmus and caribbean plate dynamics that affected sea floor and island topography the bonaire succession provides a model for understanding and predicting isolated carbonate platform development as well as architecture facies and potential diagenetic changes in an active tectonic setting

erosion of tortonian phosphatic intervals in upwelling zones the role of internal waves abstract during the miocene the upwelling is assumed to be important in the formation of many mediterranean phosphate deposits in carbonate platform successions there are different types of upwelling mechanisms such as equatorial upwellings ice edge upwellings and coastal upwellings the carbonate platforms are mainly affected by wind driven coastal upwelling systems during upwelling season the seawater in coastal areas is strongly density stratified and the permanent pycnocline rises inshore forming an inclined frontal layer the liaison between upwellings and internal waves is widely documented in the literature internal waves result from perturbations of the hydrostatic equilibrium where balance is sustained between the force of gravity and buoyant restoring force many perturbations of the pycnocline can propagate as an internal wave in a coastal upwelling a key role for wave propagation is played by permanent pycnocline the run up swash currents develop during the break of internal waves and produce erosional processes in particular the backwash return flow may induce the erosion of seafloor sediments and transport these sediments downslope as bedload erosion of phosphate rich intervals has been extensively documented the deposition of gravity flow sediments is followed by intervals of non deposition incipient lithification phosphogenesis and erosion in this work we evaluate the role of internal waves in the formation of the resedimented phosphate rich intervals characterising the basal portion of the hemipelagic orbulina marls these marls are deposited on the low angle latium abruzzi carbonate ramp and represent deposition in a foreland basin during the initial stages of evolution of the central apennine belt during the early tortonian age

global perturbation of the carbon cycle at the onset of the miocene climatic optimum the miocene climatic optimum mco ca 17 14 7 ma represents one of several major interruptions in the long term cooling trend of the past 50 m y to date the processes driving high amplitude climate variability and sustaining global warmth during this remarkable interval remain highly enigmatic we present high resolution benthic foraminiferal and bulk carbonate stable isotope records in an exceptional continuous carbonate rich sedimentary archive integrated ocean drilling program site u1337 eastern equatorial pacific ocean which offer a new view of climate evolution over the onset of the mco a sharp decline in delta o 18 and delta c 13 at ca 16 9 ma contemporaneous with a massive increase in carbonate dissolution demonstrates that abrupt warming was coupled to an intense perturbation of the carbon cycle the rapid recovery in delta c 13 at ca 16 7 ma similar to 250 k y after the beginning of the mco marks the onset of the first carbon isotope maximum within the long lasting monterey excursion these results lend support to the notion that atmospheric pco 2 variations drove profound changes in the global carbon reservoir through the mco implying a delicate balance between changing co2 fluxes rates of silicate weathering and global carbon sequestration comparison with a high resolution delta c 13 record spanning the onset of the cretaceous oceanic anoxic event 1a similar to 120 m y ago reveals common forcing factors and climatic responses providing a long term perspective to understand climate carbon cycle feedbacks during warmer periods of earth s climate with markedly different atmospheric co2 concentrations

orbitally paced climate evolution during the middle miocene monterey carbon isotope excursion one of the most enigmatic features of cenozoic long term climate evolution is the long lasting positive carbon isotope excursion or monterey excursion which started during a period of global warmth after 16 9 ma and ended at similar to 13 5 ma approximately 400 kyr after major expansion of the antarctic ice sheet we present high resolution 1 9 kyr astronomically tuned climate proxy records in two complete sedimentary successions from the northwestern and southeastern pacific odp sites 1146 and 1237 which shed new light on the middle miocene carbon isotope excursion and associated climatic transition over the interval 17 1 12 7 ma we recog nize three distinct climate phases with different imprints of orbital variations into the climatic signals 1146 and 123 7 delta 18 o delta 13 c 1237 xrt fe fraction 63 pm 1 climate optimum prior to 14 7 ma characterized by minimum ice volume and prominent 100 and 400 kyr variability 2 long term cooling from 14 7 to 13 9 ma principally driven by obliquity and culminating with rapid cryosphere expansion and global cooling at the onset of the last and most pronounced delta 13 c increase 3 icehouse mode after 13 9 ma with distinct 100 kyr variability and improved ventilation of the deep pacific the monterey carbon isotope excursion 16 9 13 5 ma consists overall of nine 400 kyr cycles which show high coherence with the long eccentricity period superposed on these low frequency oscillations are high frequency variations 100 kyr which closely track the amplitude modulation of the short eccentricity period in contrast to delta 13 c the delta 18 o signal additionally shows significant power in the 41 kyr band and the 1 2 myr amplitude modulation of the obliquity cycle is clearly imprinted in the 1146 delta 18 o signal our results suggest that eccentricity was a prime pacemaker of middle miocene climate evolution through the modulation of long term carbon budgets and that obliquity paced changes in high latitude seasonality favored the transition into the icehouse climate c 2007 elsevier b v all rights reserved

vertical thermal gradient history in the eastern equatorial pacific during the early to middle miocene implications for the equatorial thermocline development knowledge of the equatorial thermocline is essential for understanding climate changes in the tropical pacific multispecies planktic foraminiferal analyses provide a way to examine temperature distributions and thus the structure of the thermocline although the secular thermocline development has been documented back to the late miocene the early to middle miocene interval has rarely been examined in addition relationships with the dynamic antarctic ice sheets remain unclear here we investigate the vertical thermal gradient in the upper water column at integrated ocean drilling program site u1337 in the eastern equatorial pacific eep throughout the early to middle miocene 23 1 to 11 7 ma the gradient increased over the miocene climatic optimum whereas it decreased during the east antarctic ice sheet expansion eaie comparison of the eep record with its western equatorial pacific wep counterpart suggests that sea surface temperature was more stable in the wep than in the eep we further estimated equatorial thermocline from two diagonal gradients between the eep and the wep thermocline shoaled from 16 7 to 15 7 ma and tilt weakened between 16 5 and 13 8 ma the onset of the monterey excursion and the reduced antarctic ice sheet volume would have affected thermocline depth and tilt respectively thermocline depth was likely much deeper compared to pliocene to modern conditions furthermore a 4 point based distribution of isotherms 4di index was used as a metric of the evenness or unevenness of the isotherm distributions the 4di index considerably reduced at around the eaie and other mi events reflecting the evenly distributed isotherms under a more glaciated antarctica

middle miocene climate cooling linked to intensification of eastern equatorial pacific upwelling during the middle miocene earth s climate transitioned from a relatively warm phase miocene climatic optimum to a colder mode with reestablishment of permanent ice sheets on antarctica thus marking a fundamental step in cenozoic cooling carbon sequestration and atmospheric co2 drawdown through increased terrestrial and or marine productivity have been proposed as the main drivers of this fundamental transition we integrate high resolution 1 3 k y benthic stable isotope data with x ray fluorescence scanner derived biogenic silica and carbonate accumulation estimates in an exceptionally well preserved sedimentary archive recovered at integrated ocean drilling program site u1338 to reconstruct eastern equatorial pacific productivity variations and to investigate temporal links between high and low latitude climate change over the interval 16 13 ma our records show that the climatic optimum 16 8 14 7 ma was characterized by high amplitude climate variations marked by intense perturbations of the carbon cycle episodes of peak warmth at southern hemisphere insolation maxima coincided with transient shoaling of the carbonate compensation depth and enhanced carbonate dissolution in the deep ocean a switch to obliquity paced climate variability after 14 7 ma concurred with a general improvement in carbonate preservation and the onset of step wise global cooling culminating with extensive ice growth over antarctica ca 13 8 ma we find that two massive increases in opal accumulation ca 14 0 and ca 13 8 ma occurred just before and during the final and most prominent cooling step supporting the hypothesis that enhanced siliceous productivity in the eastern equatorial pacific contributed to co2 drawdown