oak leaves as biosensors of late neogene and early pleistocene paleoatmospheric co2 concentrations abstract complementary to the interpretation of 13 c values of biogenic carbonate and sedimentary organic carbon in marine sediments paleoatmospheric co 2 levels can be estimated by considering the inverse relationship between atmospheric co 2 concentration and stomatal parameters frequency size on leaves of land plants in woody plants the significance of this species specific physiological response to changing co 2 regimes is now repeatedly confirmed both experimentally and from historical sequences of leaves collected since the onset of industrialization a corollary of this relationship is that analysis of stomatal parameters on fossil leaves has the potential of determining changes in paleoatmospheric co 2 levels at different time scales well preserved cuticle remains of oak leaves from late miocene pliocene and early pleistocene sediments of the lower rhine embayment germany the netherlands give promise of extending the record of stomatal frequency response to the last 10 ma during intervals with warm temperate to subtropical climatic conditions oak leaves are characterized by a high stomatal resistance or low conductance to co 2 diffusion and low stomatal frequencies during cooler intervals we observe an opposite picture comparison with historical relations between co 2 concentration and stomatal properties suggests that paleoatmospheric co 2 concentrations were not significantly higher than during the last 200 years and fluctuated several times between 280 and 370 ppmv in covariation with contrasting regional climatic conditions on a global scale intervals with reduced co 2 levels match glacial pulses characterized by the occurrence of ice rafted detritus in high latitude oceanic sediments

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

sedimentology stratigraphy and paleoclimate at the late miocene coffee ranch fossil site in the texas panhandle abstract the late miocene coffee ranch fossil assemblage contains some of the earliest evidence of c4 herbivory in north america however little is known regarding the environmental setting associated with the fauna and a general lack of detailed paleoclimate data exists for the late miocene from the north american continental interior in this study the sedimentary environments stratigraphy geochronology and paleoclimate are interpreted for a series of outcrops of the late miocene ogallala formation in the texas panhandle that includes the coffee ranch locality updated magnetostratigraphy coupled with previously published geochronology indicates that all exposed strata were deposited over a 277 kyr interval within chron c3an 2n from 6 42 6 70 ma depositional environments include fluvial channels floodplain ponds floodplain paleosols eolian paleosols riverine tufa and reworked volcanic ash trunk and tributary fluvial channels are differentiated using channel dimensions sedimentary structures and bounding surface architecture and indicate seasonally variable discharge paleosols from nine pedofacies are described and preserve a spectrum of weakly developed entisols and weakly to moderately mature inceptisols and vertisols constitutive mass balance calculations reveal that mature paleosols formed along distinct pedogenic pathways calcic vertisols accumulated pedogenic carbonate and exhibited either net volumetric dilation or collapse as a result of mineral weathering in contrast non calcic vertisols show patterns of decalcification and variable degrees of volumetric dilation and collapse the presence of the paleosols described in this study requires paleoprecipitation between of 900 1150 mm yr approximately double modern values and a westward shift of the continental udic ustic soil moisture boundary by 400 km during the late miocene this finding suggests that climates in the southern midcontinent were not sufficiently arid to select for c4 photosynthetic pathways over c3 photosynthesis in the late miocene

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

disentangling the roles of late miocene palaeogeography and vegetation implications for climate sensitivity the impact of rising co2 on future climate remains uncertain but the evidence for high co2 in the palaeorecord suggests that past climates could provide a potentially quantifiable indication of climate in a high co2 world one such past time period is the late miocene 11 6 5 3 ma for which co2 reconstructions indicate higher levels than those of preindustrial and similar to the present atmospheric level 400 ppm the late miocene palaeorecord suggests a much warmer and wetter northern hemisphere than preindustrial however vegetation feedbacks are an important component of the climate system and vegetation distribution reconstructions from the palaeorecord have been shown to be very different to the present vegetation distribution we examine the roles that different vegetation and palaeogeography play in climate sensitivity for the late miocene and consider the implications for potential future climate change to do this we use coupled atmosphere ocean vegetation simulations of late miocene and potential modern climates forced by three different co2 concentrations with vegetation perturbation experiments and make quantitative comparisons to the palaeorecord optimal regions to target late miocene palaeodata acquisition for the purposes of informing about future climate include north america northern africa australia paraguay and southern brazil and northeastern asia these regions are those which the model results predict to be most sensitive to co2 forcing but where the local temperature response to co2 forcing is similar between the simulated potential modern and late miocene climates the model results suggest that climate sensitivity to co2 forcing is directly affected by the palaeogeographic configuration and that the inferred climate sensitivity for doubled co2 is 0 5 0 8 c higher for the late miocene than we might expect for future climate because of differences in synergy the greater land mass at high northern latitudes during the late miocene and the differences in vegetation distribution predictions that result combined with differences in ocean circulation and the effect of sea ice make the late miocene boundary conditions more sensitive to co2 forcing than the modern boundary conditions

on the causes of mid pliocene warmth and polar amplification the mid pliocene 3 to 3 3 ma ago is a period of sustained global warmth in comparison to the late quaternary 0 to 1 ma ago and has potential to inform predictions of long term future climate change however given that several processes potentially contributed relatively little is understood about the reasons for the observed warmth or the associated polar amplification here using a modelling approach and a novel factorisation method we assess the relative contributions to mid pliocene warmth from elevated co2 lowered orography and vegetation and ice sheet changes the results show that on a global scale the largest contributor to mid pliocene warmth is elevated co2 however in terms of polar amplification changes to ice sheets contribute significantly in the southern hemisphere and orographic changes contribute significantly in the northern hemisphere we also carry out an energy balance analysis which indicates that that on a global scale surface albedo and atmospheric emmissivity changes dominate over cloud changes we investigate the sensitivity of our results to uncertainties in the prescribed co2 and orographic changes to derive uncertainty ranges for the various contributing processes

soil feedback drives the mid holocene north african monsoon northward in fully coupled ccsm2 simulations with a dynamic vegetation model we explore climate vegetation interactions in mid holocene north africa with a suite of community climate system model ccsm2 simulations the ccsm includes synchronously coupled atmosphere ocean sea ice land and vegetation models the ccsm s present day precipitation for north africa compares well with simulations of other models and observations mid holocene data reveal a wetter and greener sahara compared to the present the ccsm exhibits a greater closer to the expected precipitation increase than other models and in response grasses advance from 18 75 to 22 5 n in much of north africa precipitation is enhanced locally by the northward advance of grasses but suppressed regionally mainly due to an insufficient albedo decrease with the expansion of vegetation prior studies have always lowered the surface albedo with the expansion of vegetation in north africa in the ccsm s mid holocene simulations the albedo decreases more because wetter soils are simulated darker than drier soils than due to expanding vegetation these results isolate albedo as the key ingredient in obtaining a positive precipitation vegetation feedback in north africa two additional simulations support this conclusion in the first simulation the desert s sandy soil textures are changed to loam to represent increased organic matter soil water retention and grass cover increase albedo decreases somewhat precipitation responds with a small yet widespread increase in the second simulation a darker soil color is prescribed for this region now the monsoon advances north about 4 these results illustrate a north african monsoon highly sensitive to changes in surface albedo and less sensitive to changes in evapotranspiration

link between oceanic heat transport thermohaline circulation and the intertropical convergence zone in the early pliocene atlantic planktonic foraminiferal oxygen isotope records from the western and eastern tropical pacific and atlantic oceans suggest a southward shift in the intertropical convergence zone toward its modern location between 4 4 and 4 3 ma a concomitant shift in the carbon isotope compositions of atlantic benthic foraminifera provides strong evidence for an increased thermohaline overturn at this time we suggest that the southward shift of the intertropical convergence zone and associated change in trade wind circulation altered equatorial surface hydrography increased the advection of warmer and more saline surface waters into the subtropical and north atlantic and contributed to thermohaline overturn

early and middle miocene stable isotopes implications for deepwater circulation and climate the middle miocene 18o increase represents a fundamental change in the ocean atmosphere system which like late pleistocene climates may be related to deepwater circulation patterns there has been some debate concerning the early to early middle miocene deepwater circulation patterns specifically recent discussions have focused on the relative roles of northern component water ncw production and warm saline deep water originating in the eastern tethys our time series and time slice reconstructions indicate that ncw and tethyan outflow water two relatively warm deepwater masses were produced from 20 to 16 ma ncw was produced again from 12 5 to 10 5 ma another feature of the early and middle miocene oceans was the presence of a high 13c intermediate water mass in the southern hemisphere which apparently originated in the southern ocean miocene climates appear to be related directly to deepwater circulation changes deep waters warmed in the early miocene by 3 c 20 to 16 ma and cooled by a similar amount during the middle miocene 18o increase 14 8 to 12 6 ma corresponding to the increase 20 ma and subsequent decrease 16 ma in the production of ncw and tethyan outflow water large 0 6 relatively rapid 0 5 m y 18o increases in both benthic and planktonic foraminifera i e the mi zones of miller et al 1991a and wright and miller 1992a were superimposed in the long term deepwater temperature changes they are interpreted as reflecting continental ice growth events seven of these m y glacial interglacial cycles have been recognized in the early to middle miocene two of these glacial interglacial cycles mi3 and mi4 combined with a 2 to 3 c decrease in deepwater temperatures to produce the middle miocene 18o shift

mesoscale field aligned irregularity structures fais of airglow associated with medium scale traveling ionospheric disturbances mstids in this paper we report the evolution generation amplification and dissipation of optically observed mesoscale field aligned irregularity structures fais similar to 150 km associated with a medium scale traveling ionospheric disturbance mstid event there have not been observations of mesoscale fais of airglow before the mesoscale fais were generated in an airglow depleted front of southwestward propagating mstids that were simultaneously observed by an all sky imager a gps monitor and a digisonde around xinglong 40 4 degrees n 30 5 degrees magnetic latitude china on 17 18 february 2012 a normalized cross correlation method has been used to obtain the velocities of mesoscale fais and mstids the mesoscale fais had an obvious northwestward relative velocity to main body mstids about 87 0 m s on average the direction of this relative velocity was roughly parallel to the depleted fronts furthermore the evolution of the mesoscale fais was mostly controlled by the intensity of the depleted fronts occurred in a highly elevated ionosphere that had a total electron content depletion associated with large negative airglow perturbations 25 the mesoscale fais grew rapidly when they experienced southeastward wind which had a speed of about 100 m s and were measured by a fabry perot interferometer a northeastward polarization electric field within a depleted airglow front can play a controlling role in the development of the mesoscale fais the electric field can significantly elevate the ionosphere and move the mesoscale fais northwestward by the e x b drift the processes for the generation and development of the polarization electric field and the mesoscale fais however need further study

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

miocene climate in europe patterns and evolution to improve our understanding of long term climate changes during the neogene in eurasia the international research network neclime neogene climate evolution in eurasia was established in the year 2000 in this first synthesis results of neclime activities focussing on the miocene of europe as one key area are combined to present a summary of the climate evolution in time and space more than 300 miocene fossil floras have been compiled and quantitatively analysed in terms of several climatic parameters during the last few years in this volume alone about 75 new data sets are available to synthesize the results of this volume quantitative climate maps for europe are generated on palaeogeographic maps for langhian and early tortonian for the first time characteristic climate patterns appear for each time interval and can be related to both global climate change and alpine tectonics generally the climate maps combine and support the individual results discussed in this volume for the individual regions

a 20 million year record of planktic foraminiferal b ca ratios systematics and uncertainties in pco2 reconstructions we use new and published data representing a 20 million long record to discuss the systematics of interpreting planktic foraminiferal b ca ratios b ca based reconstructions of seawater carbonate chemistry and atmospheric pco 2 assume that the incorporation of boron into foraminiferal tests can be empirically described by an apparent partition coefficient k d b ca caco 3 b oh 4 hco 3 seawater hemming and hanson 1992 it has also been proposed that there is a species specific relationship between k d and temperature yu et al 2007 as we discuss although these relationships may be robust there remain significant uncertainties over the controls on boron incorporation into foraminifera it is difficult to be certain that the empirically defined correlation between temperature and k d is not simply a result of covariance of temperature and other hydrographic variables in the ocean including carbonate system parameters there is also some evidence that k d may be affected by solution hco 3 co 2 3 ratios i e ph or by co 2 3 in addition the theoretical basis for the definition of kd and for a temperature control on k d is of debate we also discuss the sensitivity of pco 2 reconstructions to different k d temperature calibrations and seawater b ca if a k d temperature calibration is estimated using ice core pco 2 values between 0 and 200 ka b ca ratios can be used to reasonably approximate atmospheric pco 2 between 200 and 800 ka however the absolute values of pco 2 calculated are sensitive to the choice of k d temperature relationship for older time periods the absolute values of pco 2 are also dependent on the evolution of seawater b concentrations however we find that over the last 20 ma reconstructed changes in declining pco 2 across the mid pleistocene transition pliocene glacial intensification and the middle miocene climate transition are supported by the b ca record even if a constant coretop k d is used or different k d temperature calibrations and models of seawater b evolution are applied to the data the inferred influence of temperature on k d from coretop data therefore cannot itself explain the structure of a published pco 2 reconstruction tripati et al 2009 we conclude the raw b ca data supports a coupling between pco 2 and climate over the past 20 ma finally we explore possible implications of b ca based pco 2 estimates for the interpretation of other marine pco 2 proxies

late miocene vegetation reconstruction with the caraib model abstract climatic outputs from the atmospheric general circulation model echam4 coupled to a mixed layer ocean model are used as inputs to the caraib global vegetation model to reconstruct the distribution of vegetation and the biosphere carbon stocks over the continents during the late miocene tortonian the results show significant changes in the geographical distribution of vegetation during the late miocene compared to the present with a reduction of desert areas and an expansion of tropical seasonal forests which reached temperate latitudes these changes in vegetation distribution are accompanied by a moderate increase of the total biosphere carbon stock by 159 gt sensitivity tests to atmospheric co 2 have also been performed with the vegetation model only i e while keeping constant all climatic variables to their reference tortonian state these tests point out the potential importance of co 2 fertilization both regarding vegetation distribution and biosphere carbon storage the impact of an atmospheric co 2 decrease from 280 to 200 ppmv or increase from 280 to 560 ppmv on the vegetation distribution appears to be at least as large as that of the climate change between the tortonian and the present while in terms of carbon storage the impact of atmospheric co 2 is far much larger than the climatic one although the actual response of vegetation to co 2 fertilization may be much smaller than its theoretical response in the model these results emphasize the need to consider atmospheric co 2 as an important parameter for palaeovegetation reconstructions

late miocene atmospheric co2 concentrations and the expansion of c4 grasses the global expansion of c4 grasslands in the late miocene has been attributed to a large scale decrease in atmospheric carbon dioxide co2 concentrations this triggering mechanism is controversial in part because of a lack of direct evidence for change in the partial pressure of co2 pco2 and because other factors are also important determinants in controlling plant type distributions alkenone based pco2 estimates for the late miocene indicate that pco2 increased from 14 to 9 million years ago and stabilized at preindustrial values by 9 million years ago the estimates presented here provide no evidence for major changes in pco2 during the late miocene thus c4 plant expansion was likely driven by additional factors possibly a tectonically related episode of enhanced low latitude aridity or changes in seasonal precipitation patterns on a global scale or both

the neogene of eurasia spatial gradients and temporal trends the second synthesis of neclime article i nfo this volume represents the second synthesis of the international open research network neclime neogene climate evolution in eurasia that was established in 2000 to study climate change in eurasia during the neogene and its impact on ecosystems the main objectives of neclime research are 1 proxy data based quantitative reconstructions of neogene climate in eurasia by means of standardised techniques 2 the modelling of atmospheric and oceanic circulation and of biomes using neogene boundary conditions and 3 the analysis of the interaction between palaeogeography vegetation and climate presently 94 scientists from 34 countries are neclime members contributing with their published data to a collective data base integrating proxies from various sources such as palaeobotany vertebrate palaeontology and geology the following core topics are addressed in the volume precipitation patterns and landscape opening the asian monsoon systems the potential of past climates for the evaluation of future climate change scenarios as well as short term change and variability of climate highlights of the single contributions are summarised in a proxy data section and in a modelling section respectively it is shown that the integrative approach presented in this volume brings about a much better and much more detailed understanding of neogene climate dynamics in eurasia than previously achieved even though neogene climate changes may have regional aspects differing considerably from each other and from the general global trend the results from the various proxy and modelling studies consistently show that later neogene cooling implicated more pronounced latitudinal and longitudinal gradients on the other hand the issue reveals a number of problems and questions resulting from the contrary nature of palaeozoological and palaeobotanical palaeoclimate proxies and modelling results mainly at a more regional level the models can not yet explain the relatively warm high latitudes during the neogene and we still do not sufficiently understand the role of the various boundary conditions such as co2 palaeogeography and palaeovegetation in the observed neogene climate change and its regional differentiation these apparent uncertainties underline the importance of the study of palaeo scenarios in order to enhance the reliability of future climate projections

a late miocene climate model simulation with echam4 ml and its quantitative validation with terrestrial proxy data abstract for the tortonian late miocene 11 to 7 ma we present a model simulation using the atmospheric general circulation model agcm echam4 coupled to a mixed layer ml ocean model the tortonian simulation with echam4 ml includes an adjusted weaker than present ocean heat transport a generally lower palaeorography and an appropriate palaeovegetation we analyse the climatic differences between the tortonian run and the present day control experiment and we validate our tortonian model results for the mean annual temperature and the annual precipitation with quantitative terrestrial proxy data globally the tortonian run is slightly warmer 0 6 c and the global precipitation indicates more humid conditions 27 mm a than the pd control run particularly the northern high latitudes are warmer 3 5 c in the tortonian simulation which leads to a weaker meridional temperature gradient than today as well as to a reduction of polar sea ice we attribute the polar warming to the lowering of the greenland elevation 20 c in the miocene and to the effects of the palaeovegetation the reduced altitude of the tibetan plateau causes a warming 20 c as compared to today and leads to a weaker asian monsoon in the tortonian run for europe the mean annual temperature is almost unaffected as compared to today because a cooling effect of the weak palaeocean heat transport is compensated by the palaeovegetation when validating our model results we find that the tortonian run is largely consistent with quantitative proxy data however the high latitudes tend to be generally too cool in the palaeoclimate simulation and the equator to pole temperature gradient is too steep as compared to proxy data for europe the comparison with proxy data indicates that the tortonian simulation underestimates the mean annual temperatures but precipitation patterns are quite consistent between model results and proxy data overall the tortonian run is quite realistic and hence the model simulation contributes to a better understanding of the relevant climate processes in the miocene however the discrepancies to proxy data demonstrate that we still do not sufficiently understand the late miocene climate

miocene deepwater oceanography a global synthesis of miocene benthic foraminiferal carbon and oxygen isotopic and faunal abundance data indicates that miocene thermohaline circulation evolved through three regimes corresponding approximately to early middle and late miocene times there is evidence for major qualitative differences between the circulation of the modern ocean and the miocene ocean prior to 11 ma the 13c 12c ratios of the benthic foraminifera cibicidoides are interpreted in terms of water mass aging i e the progressive depletion of dissolved o2 and lowering of 13c values as the result of oxidation of organic matter as water flows further from its sources at the surface of the oceans both isotopic and faunal data indicate that the early miocene regime from 22 to 15 ma was the most different from today s during that interval intermediate and deep waters of both the atlantic and the pacific oceans aged in a northward direction and the intermediate waters of the indian the south atlantic and the south pacific oceans were consistently the youngest in the global ocean we speculate that early miocene global thermohaline circulation may have been strongly influenced by the influx of warm saline water tethyan indian saline water from the tethys into the northern indian ocean the isotopic and faunal data suggest that flow from the tethyan region into the indian ocean diminished or terminated at about 14 ma isotopic and faunal data give no evidence for north atlantic deep water nadw formation prior to about 14 5 ma with the exception of a brief episode in the early miocene from 14 5 to 11 ma nadw formation was weak and circumpolar and antarctic water flooded the deep south atlantic and south pacific as the antarctic ice cap grew from about 10 ma to the end of the miocene thermohaline circulation resembled the modern circulation in many ways in latest miocene time 6 to 5 ma circulation patterns were very similar to today s except that nadw formation was greatly diminished the distribution pattern of siliceous oozes in miocene sediments is consistent with our proposed reconstruction of thermohaline circulation major changes which occurred in circulation during the middle miocene were probably related to the closing of the tethys and may have contributed to rapid middle miocene growth of the antarctic ice cap appendices 1 4 6 and 7 are available withentire article on microfiche order fromamerican geophysical union 2000 floridaavenue n w washington dc 20009 document 88p 002 5 00 payment mustaccompany order

paleoceanographic implications of miocene deep sea hiatuses miocene paleoceanographic evolution exhibits major changes resulting from the opening and closing of passages the subsequent changes in oceanic circulation and development of major antarctic glaciation the consequences and timing of these events can be observed in variations in the distribution of deep sea hiatuses sedimentation patterns and biogeographic distribution of planktic organisms the opening of the drake passage in the latest oligocene to early miocene 25 20 ma resulted in the establishment of the deep circumpolar current which led to thermal isolation of antarctica and increased global cooling this development was associated with a major turnover in planktic organisms resulting in the evolution of neogene assemblages and the eventual extinction of paleogene assemblages the erosive patterns of two widespread hiatuses ph 23 0 22 5 ma and nh 1 20 18 ma indicate that a deep circumequatorial circulation existed at this time characterized by a broad band of carbonate ooze deposition siliceous sedimentation was restricted to the north atlantic and a narrow band around antarctica a major reorganization in deep sea sedimentation and hiatus distribution patterns occurred near the early middle miocene boundary apparently resulting from changes in oceanic circulation beginning at this time deep sea erosion occurred throughout the caribbean hiatus nh 2 16 15 ma suggesting disruption of the deep circumequatorial circulation and northward deflection of deep currents and or intensification of the gulf stream sediment distribution patterns changed dramatically with the sudden appearance of siliceous ooze deposition in the marginal and east equatorial north pacific by 16 0 to 15 5 ma coincident with the decline of siliceous sedimentation in the north atlantic this silica switch may have been caused by the introduction of norwegian overflow water into the north atlantic acting as a barrier to outcropping of silica rich antarctic bottom water the main aspects of the present oceanic circulation system and sediment distribution pattern were established by 13 5 to 12 5 ma hiatus nh 3 coincident with the establishment of a major east antarctic ice cap antarctic glaciation resulted in a broadening belt of siliceous ooze deposition around antarctica increased siliceous sedimentation in the marginal and east equatorial north pacific and indian oceans and further northward restriction of siliceous sediments in the north atlantic periodic cool climatic events were accompanied by lower eustatic sea levels and widespread deep sea erosion at 12 to 11 ma nh 4 10 to 9 ma nh 5 7 5 to 6 2 ma nh 6 and 5 2 to 4 7 ma nh 7

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

improved discrimination of volcanic complexes tectonic features and regolith properties in mare serenitatis from earth based radar mapping radar images at 70 cm wavelength show 4 5 db variations in backscatter strength within regions of relatively uniform spectral reflectance properties in central and northern mare serenitatis delineating features suggesting lava flow margins channels and superposition relationships these backscatter differences are much less pronounced at 12 6 cm wavelength consistent with a large component of the 70 cm echo arising from the rough or blocky transition zone between the mare regolith and the intact bedrock such deep probing is possible because the ilmenite content which modulates microwave losses of central mare serenitatis is generally low 2 3 by weight modeling of the radar returns from a buried interface shows that an average regolith thickness of 10 m could lead to the observed shifts in 70 cm echo power with a change in tio2 content from 2 to 3 this thickness is consistent with estimates of regolith depth 10 15 m based on the smallest diameter for which fresh craters have obvious blocky ejecta the 70 cm backscatter differences provide a view of mare flow unit boundaries channels and lobes unseen by other remote sensing methods a localized pyroclastic deposit associated with rima calippus is identified based on its low radar echo strength radar mapping also improves delineation of units for crater age dating and highlights a 250 km long east west trending feature in northern mare serenitatis that we suggest is a large graben flooded by late stage mare flows

miocene benthic foraminiferal cd ca records south atlantic and western equatorial pacific cadmium to calcium records in benthic foraminifera interpreted in conjunction with carbon isotope records reflect oceanic circulation patterns and oceanic inventories of cd carbon 13 carbon 12 and indirectly phosphorus cd ca ratios have been determined in benthic foraminifera cibicidoides spp for the late middle and early miocene from a site in the south atlantic deep sea drilling project dsdp site 525 leg 74 2500 m walvis ridge and from a site in the western equatorial pacific dsdp site 289 leg 30 2200 m ontong java plateau both sites have well established carbon isotope records for benthic foraminifera typical of the global record dominated by inventory changes cd ca ratios and carbon isotope values were averaged for the miocene in time intervals substantially longer than estimated oceanic residence times of cd c or p oceanic mean cd ca and carbon isotopes were estimated as weighted means of the values from both sites using weighting factors based on replicating modern oceanic means this may tend to underestimate oceanic inventories earlier than the late miocene because of changing water mass dominance at the south atlantic site from these means the oceanic cd inventory appears relatively stable during the miocene while there are large changes in carbon isotope inventories miocene cd inventory estimates are at least 20 lower than published estimates for quaternary stages 1 and 2 increasing oceanic cd inventories over the past 10 m y are consistent with hypotheses of increased river fluxes in the recent geologic past cd ca differences between sites may be indicative of the extent of basin basin fractionation from bottom water circulation although the validity of this comparison depends on how representative each of these two sites is through time for its respective ocean basin the pacific atlantic cd ca difference based on these two sites was larger in the late miocene compared to the middle and early miocene the relationship between cd ca and carbon isotope inventories and intersite gradients for these sites suggests that either oceanic phosphorus inventories or parameters related to marine organic matter composition must have been different in the miocene than at present large changes in the carbon isotope balance reflected as both positive and negative excursions in the carbon isotope inventories occurred with little effect on cd inventories changes in phosphorus fluxes associated with these carbon isotope flux changes may have been compensated for by changing deposition fluxes to other phosphorus sinks phosphorus inventories may have increased from the middle to late miocene with increasingly negative oceanic carbon isotope inventories however confirmation of these suggestions depend on collecting more cd ca and 13c data throughout the miocene oceans and on developing the application of other constraints for these interpretations

miocene evolution of atmospheric carbon dioxide changes in pco2 or ocean circulation are generally invoked to explain warm early miocene climates and a rapid east antarctic ice sheet eais expansion in the middle miocene this study reconstructs late oligocene to late miocene pco2 from ep values based on carbon isotopic analyses of diunsaturated alkenones and planktonic foraminifera from deep sea drilling project sites 588 and 608 and ocean drilling program site 730 our results indicate that highest pco2 occurred during the latest oligocene 350 ppmv but decreased rapidly at 25 ma the early and middle miocene was characterized by low pco2 260 190 ppmv lower intervals of pco2 correspond to inferred organic carbon burial events and glacial episodes with the lowest concentrations occurring during the middle miocene there is no evidence for either high pco2 during the late early miocene climatic optimum or a sharp pco2 decrease associated with eais growth paradoxically pco2 increased following eais growth and obtained preindustrial levels by 10 ma although we emphasize an oceanographic control on miocene climate low pco2 could have primed the climate system to respond sensitively to changes in heat and vapor transport

effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation the late cenozoic closure of the seaway between the north andsouth american continents is thought to have caused extensive changes in ocean circulation and northern hemisphere climate1 2 but the timing and consequences of the emergence of the isthmus of panama which closed the seaway remain controversial1 2 3 4 5 here we present stable isotope and carbonate sand fraction records from caribbean sediments which when compared to atlantic and pacific palaeoceanographic records indicate that the closure caused a marked reorganization of ocean circulation starting 4 6 million years ago shallowing of the seaway intensified the gulf stream and introduced warm and saline water masses to high northern latitudes these changes strengthened deep water formation in the labrador sea over the next million years as indicated by an increased deep water ventilation and carbonate preservation in the caribbean sea and favoured early pliocene warming of the northern hemisphere the evaporative cooling of surface waters during north atlantic deep water formation would have introduced moisture to the northern hemisphere although the pronounced intensification of northern hemisphere glaciation between 3 1 and 2 5 million years ago substantially lagged the full development of north atlantic deep water formation we propose that the increased atmospheric moisture content was a necessary precondition for ice sheet growth which was then triggered by the incremental changes in the earth s orbital obliquity