climate stability across the eocene oligocene transition southern argentina fossil mammal teeth from mid latitude southern argentina 46 s that closely bracket the eocene oligocene transition show no resolvable change in oxygen isotope compositions in combination with paleofloral observations and geographic considerations this finding implies not only that climate was essentially constant despite interpretations elsewhere for major mid and high latitude cooling but also that evolution of hypsodonty did not coincide with climate change during the eocene oligocene transition one possible explanation for eocene oligocene transition climatic stability is that southern high latitude cooling increased latitudinal temperature gradients and strengthened ocean circulation gyres including the southward flowing brazil current in the western south atlantic regionally increased heat transport in the western atlantic offset global cooling producing a nearly constant temperature in southern south america a more radical interpretation supported by some marine data is that the paradigm of major global cooling at the eocene oligocene transition is largely false in that mean sea surface temperatures changed very little

cambrian volcanism in nova scotia canada cambrian volcanic rocks in nova scotia occur in small grabens or half grabens in the avalon zone composite terrane as part of a thin sequence of continental to shallow marine cambro ordovician ro

late devonian early carboniferous volcanism in western cape breton island nova scotia the fisset brook formation of western cape breton island and its equivalents at macmillan mountain and the north baddeck river are examples of late devonian and early carboniferous volcanic sequences associated with the formation of post acadian successor basins in the northeastern appalachians they consist of bimodal basalt rhyolite suites interbedded with alluvial fan lacustrine and rare fluvial sediments the earliest volcanic products are rhyolites and somewhat evolved basalts associated with coarse sediments followed by tholeiitic to transitional basalt flows interlayered with lacustrine type deposits geochemical studies on the fisset brook formation indicate extensive remobilization of alkalies ca rb and sr making these elements inappropriate for determining tectonic setting or magmatic affinity use of less mobile elements ti nb y and zr suggests that the basalts are tholeiitic and that the apparent alkalinity of the type section lavas is a result of alteration we conclude that volca

turtle crocodilian and champsosaur diversity changes in the cenozoic of the north central region of western united states abstract the generic diversity of large bodied reptiles turtles crocodilians and champsosaurs in the northern great plains and eastern slope of the northern rocky mountains of the united states is greatest in the early cenozoic lowest in the middle cenozoic and moderately high in the late cenozoic with the exception of a major decline in the latest tertiary the record of large tortoises indicates that these declines were not the result of critically cool winter temperatures except in glacial periods recent times and the paleocene the major declines in the middle cenozoic and latest tertiary appear to reflect mild winters about 13 c or above for cold month mean temperature but with annually or seasonally dry climates resulting in few bodies of permanent surface waters

submesoscale physical biogeochemical coupling across the ligurian current northwestern mediterranean using a bio optical glider a bio optical autonomous underwater gliding vehicle equipped with a conductivity temperature depth ctd sensor an oxygen sensor backscatter meters chromophoric dissolved organic matter cdom and chlorophyll fluorometers and upwelling and downwelling radiometers was developed to characterize the biogeochemical response to physical forcing at the submesoscale 1 10 km winter data obtained in the northwestern mediterranean basin in a 50 km transect that crossed the permanent along coast ligurian current show tight physical biogeochemical coupling across the ligurian current not observed using other sampling strategies at the scale of the transect the various biogeochemical parameters displayed independent behaviors while at the submesoscale there was a coherent covariance of these variables especially in the frontal zone near isopycnal tongues of elevated fluorescence and oxygen concentration were recorded down to a depth of 180 m and are the likely signature of a converging horizontal and downwelled water flow local anomalies in a horizontal section well below the mixed layer depth are likely representative of downwelled waters from the euphotic layer intrusions of elevated cdom concentrations together with signatures of smaller particles are the likely features of a local divergence and upwelled waters from subjacent aphotic layers these are particularly apparent in the form of local anomalies in a horizontal section within the mixed layer similar tongues were observed in data from subsequent glider deployments such biogeochemical signatures enable the identification of upward and downward physical motions not observed by other technologies reinforcing the need for coupled high resolution physical biogeochemical studies not only for investigating biogeochemical processes themselves but also for resolving physical processes at these scales

sources and flow patterns of deep ocean waters as deduced from potential temperature salinity and initial phosphate concentration through the deconvolution of ocean chemical data it has been shown that the ratio of o2 utilization to phosphate production in the sea is 175 6 rather than 138 as proposed by redfield et al 1963 we find no evidence that this ratio changes significantly with location or depth in the sea we have used this new ratio to calculate the initial phosphate concentrations for the waters sampled during the geosecs and tto programs the important application of these new results is in constraining the origin and flow patterns of deep waters in the ocean we believe that a strong case can be made that antarctic salinity maximum water i e the common water of montgomery 1958 is produced by the mixing of waters entering the antarctic from mid depths in the indian pacific and atlantic with weddell sea bottom water southern component antarctic common water consists of about 45 weddell sea bottom water 30 intermediate waters from the pacific and indian oceans and 25 deep water originating from the northern atlantic

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

intensification of ocean fronts by down front winds abstract many ocean fronts experience strong local atmospheric forcing by down front winds that is winds blowing in the direction of the frontal jet an analytic theory and nonhydrostatic numerical simulations are used to demonstrate the mechanism by which down front winds lead to frontogenesis when a wind blows down a front cross front advection of density by ekman flow results in a destabilizing wind driven buoyancy flux wdbf equal to the product of the ekman transport with the surface lateral buoyancy gradient destabilization of the water column results in convection that is localized to the front and that has a buoyancy flux that is scaled by the wdbf mixing of buoyancy by convection and ekman pumping suction resulting from the cross front contrast in vertical vorticity of the frontal jet drive frontogenetic ageostrophic secondary circulations ascs for mixed layers with negative potential vorticity the most frontogenetic ascs select a preferred cross front width and do not translate with

did impacts volcanic eruptions or climate change affect mammalian evolution abstract in recent years it has become popular to attribute faunal change and mass extinction to impacts volcanic eruptions or climatic change how well do these supposed causes compare to the excellent record of cenozoic life especially that of fossil mammals two different cenozoic mammal diversity curves were compared and important climatic volcanic and impact horizons were examined in detail in no case is there a strong correlation between impacts eruptions or climatic events and any episode of mammalian turnover on the contrary most of the known impact eruption and climatic events of the cenozoic occurred during intervals of faunal stability conversely episodes of high turnover and faunal change among cenozoic mammals correlate with no known extrinsic causes apparently extrinsic environmental factors such as impacts eruptions and climate change have a minimal effect and intrinsic biological factors must be more important

factors affecting the spatial pattern of the deep chlorophyll maximum in the region of the azores front abstract results are given of two surveys of the deep chlorophyll maximum dcm in the vicinity of an oceanic front south west of the azores the surveys made in late april and may 1981 used mainly a towed undulating fish seasoar fitted with ctd and in situ fluorometer in the latter survey observations of underwater irradiance nitrate concentration and primary production were also made the front was baroclinic and is considered to be an arm of the gulf stream return flow in the north east atlantic the current associated with the front made a large meander through the area and during the observation period shed an eddy which later drifted westwards the front separated two distinct water types which were termed east atlantic water eaw and west atlantic water waw the dcm in waw was on average 20 m deeper and between 50 and 60 of the magnitude of that in eaw however the 1 light level coincided with the depth of the dcm in both water types and this fact together with observations on the different nitrate concentrations in the two water types led to the theory that the differences in the dcm could be explained by assuming an overall lower level of primary productivity in waw although differences in vertical mixing may have been a contributory factor the measurements of primary production imply that the specific growth rate of phytoplankton in the dcm was less than 0 1 day 1 in the front itself there was some evidence for small scale 20 km eddy like features which produced patchiness of the same scale in the dcm there was also evidence for advective intrusions along isopycnals of eaw across the front into waw in two cases this process produced deep subsidiary maxima below the dcm with chlorphyll a concentrations of 0 1 mg m 3 as deep as 170 m in the late april survey two of the seasoar sections showed higher phytoplankton chlorophyll concentrations on the eaw side of the front but in general on both surveys there was little evidence for increased phytoplankton biomass associated with the front

methyl mercury distributions in relation to the presence of nano and picophytoplankton in an oceanic water column ligurian sea north western mediterranean recent findings on the distribution of methylated mercury mehgt in waters have highlighted the importance of organic carbon remineralization on the production of these compounds in the open ocean here we present the first time series 20 monthly samplings between july 2007 and may 2009 of high resolution vertical profiles 10 12 depths in a 2350 m water column of mehgt distributions in an open ocean environment the ligurian sea north western mediterranean sea concentrations varied within the sub picomolar range general mean 0 30 0 17 pmol l 1 n 214 with the lowest values at the surface increasing with depth up to the oxygen minimum zone and decreasing slowly at greater depth concentrations in the surface waters never exceeded 0 15 pmol l 1 while the highest concentrations up to 0 82 pmol l 1 were associated to the hypoxycline during the autumn bloom a detailed vertical mehgt profile reveals a double peak pattern coincidental with the two microbial layers described by tanaka and rassoulzadegan 2002 the so called microbial food web in the euphotic zone 100 m temporal variations in the mehgt abundance and distribution in the water column were linked to seasonality the highest mehgt concentrations were found in the oxygen minimum zone during the period of stratification and coincide with the greatest abundance of nano and picophytoplankton cyanobacteria nanoflagellates etc in the euphotic layer none of our deep mehgt measurements 100 m above the sea bottom revealed a significant sedimentary source of mehgt we explored the correlation between mehgt concentrations and the apparent oxygen utilization a proxy of organic matter remineralization over the study period results of this study strengthen the hypothesis that net mercury methylation in the open ocean occurs in the water column is linked to organic matter regeneration and is promoted by the presence of small sized nano and picophytoplankton that dominate under oligotrophic conditions 2010 elsevier ltd all rights reserved

the eocene oligocene boundary event in the deep sea analysis of middle eocene to early oligocene calcareous and siliceous microfossils shows gradual biotic changes with no massive extinction event across the eocene oligocene boundary biotic changes in the late paleogene appear to reflect changing paleoclimatic and paleoceanographic conditions and do not support suggestions of a catastrophic biotic event caused by a bolide impact at the eocenel oligocene boundary

biological and chemical signs of upward motions in permanent geostrophic fronts of the western mediterranean upward motions are often invoked to explain the high productivity of permanent geostrophic fronts in the western mediterranean while physical evidence of such upward advections is seldom reported the goal of this study is to define biological and chemical criteria which can be used to localize such upward motions zones we use a one dimensional time dependent model of phytoplankton dynamics to test the effects of upward advection on the vertical distribution of phytoplankton biomass nutrients and dissolved oxygen simulations also include the effects of advective motions of the phytoplankton cells in the light field on phytoplankton growth in conformance with the continuity equation boundary conditions were defined to allow horizontal flow of the upwelled water within the upper mixed layer low upward advections 3 m d led to a shallowing and sharpening of the nitracline oxycline and deep maxima of phytoplankton biomass and oxygen and to an increase in phytoplankton biomass by confining the phytoplankton nutrient system in the surface mixed layer higher upward advections lead to homogeneous phytoplankton biomass and oxygen vertical distributions in the upper mixed layer the nitracline and the oxycline being then at the top of the pycnocline data collected during the prolig 2 cruise may 1985 on the heavy side of the liguro provenqal front are interpreted as an illustration of these numerical results computed primary production rates are compared with measurements conducted in the almer a oran front during the almofront i cruise april 1991 in a similar situation in both fronts upward advections of 1 2 m d would be sufficient to account for the observed vertical distributions and the increased primary production ecological implications for the phytoplankton nutrient system are discussed particularly the spatial uncoupling of phytoplankton biomass and primary production in permanent geostrophic fronts 1 introduction the liguro provengal front b thoux et prieur 1983 sournia et al 1990 and the almerfa oran front cheney and doblar 1982 tintor et al 1988 are permanent geostrophic structures in the western mediterranean both fronts are areas of high plankton biomass in contrast with two adjacent oligotrophic type systems lohrenz et al 1988 tintor et al 1988 sournia et al 1990 prieur et al 1993 claustre et al 1994b and show net change in both the specific composition of the autotrophic claustre et al 1994b and the heterotrophic boucher et al 1987 thibault et al 1994 communities several features indicate that the two fronts are sites of enhanced production in response to geostrophic frontal dynamics in addition to the main geostrophic flow a secondary circulation exists i e the ageostrophic flow which is characterized by enhanced vertical advections as shown for example by dewey et al 1991 in the california current it is thought that upward advections in the frontal zone upwell nutrients into the photic zone and enhance primary production lohrenz et al 1988 fideau et al 1994 the resulting high biomass is then downwelled by the conver paper number 98jc01537 0148 0227 98 98 jc 01537509 00 gent part of the ageostrophic circulation along the isopycnals claustre et al 1994a b fideau et al 1994 however physical evidence for upward advection in the two fronts is not well documented see however tintor et al 1991 and l iudez and tintor 1996 and poorly understood this paper defines criteria from the vertical distribution of parameters involved in primary production which can be used to localize with some confidence the upward motions in such frontal zones in a previous modeling study zakardjian and prieur 1994 two types of phytoplankton nutrient systems resulting from high and low turbulent regimes htr and ltr respectively were described with the ltr representing the ecological conditions in the waters adjacent to the liguro provengal and almerga oran fronts where the vertical structure is controlled by diffuse vertical fluxes we use a modified version of this previous one dimensional vertical model presented in section 2 to test the sensitivity of the ltr system when an upward advection term is added in section 3 we describe the steady state vertical distribution of phytoplankton biomass nutrients and dissolved oxygen obtained with upward advection values ranging from 0 to 5 m d effects of upward advection on the vertical distribution of primary production on phytoplankton growth and finally on the productivity indexes of the water column are detailed in section 4 we present multiparametric 27 849

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

the eocene oligocene ungulates from western europe and their environment abstract a survey of paleogene ungulates from western europe is drawn up from the results of previous work on the ungulate lineages of this period and from new data on two groups particularly representative of the oligocene ungulate fauna the ruminants and the cainotheriidae based on new material collected in localities of the quercy phosphorites the history of ungulates from western europe at the eocene oligocene transition is marked by different phases of extinction and origination related to environmental changes in this perspective the relative diversity of groups and the modifications of their tooth morphology which reflect a diet change resulting from vegetation modifications are analysed from the early eocene to the late oligocene in western europe the late eocene and the early oligocene was a period of transition with an important change in faunal and floral composition the diversity analysis of ungulates suggests that the grande coupure is the result of gradual climatic and geographic events that occurred from the middle eocene mammalian paleogene mp 13 14 reference levels to the early oligocene mp 21 22 reference levels during this period it has been demonstrated that important adaptive changes occurred in the ungulate dental pattern selenodonty in artiodactyls semihypsodonty in perissodactyls and appendicular skeleton fusion of the cuboid and navicular bones of the tarsus in artiodactyls these morphological modifications coincided with environmental changes that were less extreme than in north america

faunal turnovers of palaeogene mammals from the mongolian plateau most orders and many families of modern mammals were established during the palaeogene mammalian evolution during this period of time has been correlated with global climatic events1 2 3 4 although the timing mode and scale of such a climate evolution link remain debatable1 5 6 the palaeogene global climate was step punctuated by a warming across the palaeocene eocene boundary about 55 myr ago and a cool off throughout the late eocene and early oligocene epochs1 2 7 8 9 10 the most severe cooling was at 33 5 myr slightly after the eocene oligocene boundary and was characterized by a drop in the mean annual temperature and by changes in vegetation from eocene dense forests to oligocene more open country5 here we analyse 33 palaeogene mammal faunas from the mongolian plateau of china and mongolia there is a distinct pattern of faunal turnovers perissodactyl dominant faunas of the eocene were abruptly replaced by rodent lagomorph dominant faunas of the oligocene we interpret the turnovers as having been effected by global climatic shifts and name the prominent biotic reorganization across the eocene oligocene boundary the mongolian remodelling which correlates to the european grande coupure

testing patterns and causes of faunal stability in the fossil record with an example from the pliocene lusso beds of zaire abstract two central issues emerge from recent discussions of coordinated stasis in the fossil record testing pattern and testing causality testing the generality of brett and baird s observations of faunal stability in the paleozoic appalachian foreland basin is important to determine whether such clustering of evolutionary and ecological change into relatively brief intervals of time is a general phenomenon in the fossil record or a quirk of that particular time and place methods for assessing the linkage between paleoecological and evolutionary change are discussed using examples drawn from the molluscan faunas of the pliocene edward mobutu basin of zaire and uganda in the late pliocene lusso beds of eastern zaire an interval of paleoecological and morphological stability appears to be terminated by an episode of coordinated change this paper illustrates a quantitative approach to simultaneously testing for the presence of coordinated change in paleoecological composition and species morphology with due attention to taphonomic and stratigraphic controls testing for the generality of faunal stability in the fossil record is a relatively straightforward exercise causality however is a thornier issue three broad classes of explanation for the presence of coordinated faunal change in the fossil record can be identified in the literature these span a continuum from the purely evolutionary through combined evolutionary ecological to purely ecological explanations i argue here that the critical test to distinguish between different causal hypotheses for coordinated faunal stability and turnover is an examination of correlation between environmental change and biotic change in the fossil record

two dimensional ageostrophic secondary circulation at ocean fronts due to vertical mixing and large scale deformation 1 ageostrophic secondary circulation asc in frontal data sets have been previously diagnosed using only adiabatic versions of omega equations this study includes the effect of vertical mixing on such diagnostics modified quasi geostrophic and semigeostrophic balance equations are examined for the existing azores front data sets and idealized fronts in the presence of diabatic vertical mixing as well as a large scale deformation field the relevant dimensionless parameter representing the relative importance of large scale deformation and vertical mixing is the inverse of the ekman number based on the deformation rate h2 ao where is large scale deformation rate h is vertical scale of the front and ao is the maximum vertical eddy viscosity when this parameter is smaller than o 102 the influence of vertical mixing may be important other relevant parameters include burger number bu and prandtl number pr the vertical velocity in ascs caused by diabatic mixing in all diagnostics solutions except for large bu cases shows good agreement with the garrett loder scaling the structure of ascs is found to be sensitive to pr the diagnostics of ascs for the azores front data set indicates that the vertical mixing intensifies the asc in the upper ocean 100 m and should not be neglected when the large scale deformation rate is o 10 6 s 1 or smaller the magnitude of vertical velocity in ascs due to mixing contributions reaches o 10 m d 1 with downwelling on the dense side and upwelling on the less dense side of azores front

eocene oligocene latitudinal climate gradients in north america inferred from stable isotope ratios in perissodactyl tooth enamel abstract the eocene oligocene transition 34 ma was one of the most pronounced episodes of climate change of the cenozoic in order to investigate this episode of global climate cooling in north america we analyzed the carbon and oxygen stable isotope composition of the carbonate component of 19 perissodactyl horse and rhino tooth enamel samples from the eocene oligocene rocks of the cypress hills formation southwestern saskatchewan canada we then compared the results with previously published data from the us great plains nebraska south dakota and wyoming average 1 perissodactyl enamel 13 c values vs v pdb in the eocene 8 8 0 3 and oligocene 9 0 0 3 are indistinguishable suggesting no major change in mean annual precipitation in saskatchewan across the transition the 13 c values in saskatchewan indicate the presence of arid ecosystems and are slightly higher than those in the us great plains suggesting drier conditions at higher latitudes with respect to oxygen isotopes average 1 perissodactyl enamel 18 o values vs v smow in the eocene 19 8 2 0 and oligocene 20 1 3 6 are also indistinguishable suggesting no change in the 18 o of meteoric precipitation across the transition in saskatchewan enamel 18 o variability is much larger in the oligocene vs eocene indicating a large increase in temperature seasonality this increase in enamel 18 o variability is much larger than that recorded in the us great plains suggesting that higher latitudes are more sensitive to major episodes of climate change with respect to temperature seasonality finally our data indicate no major change in the oligocene vs eocene latitudinal gradient in local water 18 o in north america which suggests no change in mean annual temperature gradients across the transition this result supports the hypothesis that ascribes the climate change of the transition to a drop in atmospheric p co 2 because climate models show that this mechanism produces uniform cooling at mid latitudes

paleopedology of the chadron formation of northwestern nebraska implications for paleoclimatic change in the north american midcontinent across the eocene oligocene boundary abstract the big cottonwood creek member is a newly recognized lithostratigraphic unit of the chadron formation of northwestern nebraska i measured 23 superimposed paleosol profiles within 29 m of strata exposed 0 4 km 0 25 mile east of the type section of the big cottonwood creek member at toadstool park in northwestern nebraska and recognized four main types of paleosols the paleosols are all well drained moderately alkaline to alkaline oxidized and range from weakly developed azonal ustifluvents to moderately and well developed paleustalfs and argiustolls with argillic and petrocalcic horizons based on changes in soil structure horizons root traces and geochemical trends these paleosols record a gradual change from humid forested conditions of the late eocene to more seasonal semi arid open range conditions leading up to the global climatic deterioration event of the early oligocene at 33 2 ma this interpretation is supported by associated changes in sedimentology fluvial architecture floras and faunas over this period of time the section at toadstool park is significant in that it establishes a link between the big badlands of south dakota and correlative deposits of wyoming the contact of the chadron and brule formations in the big badlands of south dakota is marked by an unconformity that is in part correlative to the earliest oligocene sediments that elsewhere record the global climatic deterioration event at 33 2 ma the paleosols of the big cottonwood creek member of northwestern nebraska fill in a significant part of this gap and record paleoclimatic conditions of the late eocene leading up to the global climatic deterioration event of the early oligocene using the latest lithostratigraphic biostratigraphic magnetostratigraphic and tephrostratigraphic data for the white river group this change to more arid conditions in the midcontinent appears to have progressed from west to east over time

paleogene postcompressional intermontane basin evolution along the frontal cordilleran fold and thrust belt of southwestern montana the paleogene renova formation is the earliest record of postcompressional sedimentation within and adjacent to the helena salient of the cordilleran fold and thrust belt in southwestern montana paleocurrent and compositional data from basin margin facies document radiating paleodispersal away from high relief 2 km highlands coincident with modern mountainous areas source rocks within the paleohighlands included the same archean metamorphic proterozoic paleozoic and mesozoic sedimentary and mesozoic plutonic and vo l canic rocks as exposed in modern uplifts paleocurrent and compositional data from trunk fluvial conglomerates and sandstones document the existence of an interbasinal drainage system that connected the three forks western gallatin and townsend basins with headwaters farther to the west and southwest near the present day montana idaho border overall the distribution of paleogene mountainous areas and basins closely resembled modern geography and the paleogene drainage network was strikingly similar to the modern missouri river headwater system the renova formation records the early stages of decay of the cordilleran orogenic belt including the evolution of a complex intermontane basin network in southwestern montana high energy late cretaceous to early eocene fluvial systems carved deep large scale paleovalleys into the orogenic wedge along zones of structural and stratigraphic weakness at least a 5 km thickness of overburden was removed during this time incision was temporally correlative with early cenozoic regional uplift and subtropical climatic conditions subsequent deposition of the renova formation was temporally correlative with the cessation of uplift the initiation of crustal extension and climatic cooling however extension is not interpreted to have played a major role in earliest basin development

tertiary climatic changes at middle latitudes of western north america abstract a new multivariate analysis of leaf physiognomy provides the basis for estimating various climatic parameters for angiosperm leaf assemblages estimates from this climate leaf analysis multivariate program clamp are both accurate valid and precise repeatable application of clamp to fossil leaf assemblages from western north america confirms that eocene mean annual temperature mat was generally high early eocene mat 19 c at paleolat 70 n and 27 c at paleolat 45 n significant fluctuations 5 8 in mat occurred during the eocene each successive warm period was cooler than the preceding warm period mean annual range of temperature mart was generally low during the eocene especially at middle latitudes but then markedly increased by 12 13 c at 33 ma as mat decreased by 7 8 c these changes at 33 ma largely involved a decrease in cold month mean temperature which continued to decline into the early miocene but then increased significantly into the mid miocene thermal optimum warm month mean temperature changed little from the eocene through the early miocene this parameter however markedly decreased at 13 ma which coincides with the growth of the east antarctic ice sheet clamp also indicates that the coastal region of western north america had significantly higher mat than interior regions such as the great basin and rocky mountains these differences in mat appeared by or during the eocene and indicate that much of the interior had high altitudes in the paleogene these inferences have a significant bearing on global circulation models proposed for tertiary climates

spreading of levantine intermediate waters by submesoscale coherent vortices in the northwestern mediterranean sea as observed with gliders since 2007 gliders have been regularly deployed in the northwestern mediterranean sea a crucial region regarding the thermohaline circulation of the mediterranean sea it revealed for the first time very warm 10 48c and saline 10 1 submesoscale anticyclones at intermediate depth characterized by a small radius 5 km high rossby 0 3 and burger 0 7 numbers they are likely order of 10 to be formed each year have a life time order a year and certainly contribute significantly to the spreading of the levantine intermediate waters liw toward the whole subbasin thus potentially impacting wintertime vertical mixing through hydrographical and dynamical preconditioning they could be mainly formed by the combined action of turbulent mixing and flow detachment of the northward flow of liw at the northwestern headland of sardinia upwelling conditions along the western coast of sardinia associated with a southward geostrophic flow within the upper layers seem to play a key role in their formation process

faunal stability during the early oligocene climatic crash abstract traditional neo darwinism views species as highly flexible entities which adapt to climatic change by gradually evolving new morphologies of the 177 species of mammals from the upper eocene lower oligocene 37 30 ma white river group in the high plains most species are static for 2 4 million years on average and some persist much longer only three examples of gradualism can be documented in the entire fauna and these are mostly size changes contrary to expectations most mammalian species show no change during the earliest oligocene climatic crash 33 2 ma in spite of the fact that the vegetation changed from dense forests to open forested grassland mean annual temperatures dropped 13 c and conditions got much drier and more seasonal only a few mammalian lineages speciated a few more went extinct and the vast majority 62 out of 70 persisted through this climatic event with no observable response whatsoever this evidence shows that organisms are much less responsive to the environment than short term neontological studies suggest

a latest chadronian late eocene mammalian fauna from the cypress hills saskatchewan the kealey springs west ksw local fauna from the cypress hills formation eocene to miocene saskatchewan is probably latest chadronian in age and is the northernmost assemblage representing a time near the eocene oligocene boundary in north america presence of pseudocylindrodon neglectus is strong evidence that the assemblage is chadronian herpetotherium valens protosciurus namatomys cf n lloydi and centimanomys also suggest a chadronian age the assemblage contains adjidaumo maximus and palaeolagus cf p hemirhizis species that have been cited as characteristic of the early part of the orellan land mammal age early oligocene and the typically orellan heliscomys hatcheri and eumys elegans several other tara in the ksw assemblage are known from both the chadronian late eocene and orellan

sub surface small scale eddy dynamics from multi sensor observations and modeling the study of mesoscale and submesoscale hereafter sub mesoscale hydrodynamic features is essential for understanding thermal and biogeochemical exchanges between coastal areas and the open ocean in this context a glider mission was conducted in august 2008 closely co located and almost simultaneously launched with a jason 2 altimetric pass to fully characterize the currents associated with regional sub mesoscale processes regularly observed to the north of mallorca mediterranean sea a synoptic view from satellite remote sensing fields before and during the glider mission provided a descriptive picture of the main surface dynamics at the balearic basin scale to quantify the absolute surface geostrophic currents the coastal altimetry derived current computation was improved and cross compared with its equivalent derived from glider measurements model simulations were then validated both qualitatively and statistically with the multi sensor observations the combined use of modeling and multi sensor observational data reveals the baroclinic structure of the balearic current and the northern current and a small scale anticyclonic eddy observed northeast of the mallorca coast current 15 cm s 180 m deep this mesoscale structure partially intercepted by the glider and along track altimetric measurements is marked by relatively strong salinity gradients and not as is more typical temperature gradients finally the use of the validated model simulation also shows that the geostrophic component of this small scale eddy is controlled by sub surface salinity gradients we hypothesize that this structure contains recently modified atlantic water arriving from the strait of ibiza due to a northerly wind which strengthens the northward geostrophic circulation

large temperature drop across the eocene oligocene transition in central north america the eocene oligocene transition about 33 5 million years ago was a major global climate event the end of the eocene was unusually warm with no significant ice on antarctica but the oligocene saw the arrival of a permanent antarctic ice sheet two papers this week relate to the continental effects of this global change dupont nivet et al examined sedimentary records from the tibetan plateau and find a drop in atmospheric water which caused cooling and aridification coincident with antarctic cooling previous studies attributed this phenomenon to the rapid uplift of the tibetan plateau but this new work suggests that regional tibetan climate was influenced by global events in an unrelated paper on the same climate transition zanazzi et al explore the cooling in north america at the time using stable isotope measurements from fossil teeth and bones to create a proxy temperature record they find a large drop in mean annual temperature of 8 2 c a greater fall than seen in the oceans this continental transition may explain why many cold blooded reptiles and amphibians became extinct whereas mammals able to regulate their body temperature escaped relatively unscathed an analysis of fossil tooth enamel and fossil bones is used to derive a continental temperature record for the eocene oligocene transition and reports a large drop in mean annual temperature over roughly 400 000 years this cooling explains the decline in cold blooded terrestrial animals whereas most mammals in the region were unaffected the eocene oligocene transition towards a cool climate 33 5 million years ago was one of the most pronounced climate events during the cenozoic era1 the marine record of this transition has been extensively studied however significantly less research has focused on continental climate change at the time yielding partly inconsistent results on the magnitude and timing of the changes2 3 4 5 6 7 8 here we use a combination of in vivo stable isotope compositions of fossil tooth enamel with diagenetic stable isotope compositions of fossil bone to derive a high resolution about 40 000 years continental temperature record for the eocene oligocene transition we find a large drop in mean annual temperature of 8 2 3 1 c over about 400 000 years the possibility of a small increase in temperature seasonality and no resolvable change in aridity across the transition the large change in mean annual temperature exceeding changes in sea surface temperatures at comparable latitudes9 10 and possibly delayed in time with respect to marine changes by up to 400 000 years explains the faunal turnover for gastropods amphibians and reptiles whereas most mammals in the region were unaffected our results are in agreement with modelling studies that attribute the climate cooling at the eocene oligocene transition to a significant drop in atmospheric carbon dioxide concentrations

vorticity and vertical circulation at an ocean front abstract density and velocity data with 4 km horizontal resolution from a survey of a front during fasinex frontal air sea interaction experiment are combined to describe the structure of the top 300 m of the ocean the geostrophic velocity field is derived and is used to examine the relative importance of stratification relative vorticity and twisting terms in ertel s potential vorticity q tenfold isopycnic changes in q are found across a horizontal scale of only 10 km these changes are confined to isopycnals that outcrop from the seasonal thermocline into the mixed layer the ageostrophic velocity field is quantified by solution of the omega equation and vertical velocities of up to 40 m day 1 are found small 40 km surface trapped top 200 m eddies are found to play a crucial role in the transport and effective diffusion of properties across the thermocline out of the mixed layer

ocean processes underlying surface clustering ageostrophic ocean processes such as frontogenesis submesoscale mixed layer instabilities shelf break fronts and topographic interactions on the continental shelf produce surface divergent flows that affect buoyant material over time this study examines the ocean processes leading to clustering i e the increase of material density over time on the ocean surface the time series of divergence along a material trajectory the lagrangian divergence ld is the flow property driving clustering to understand the impacts of various ocean processes on ld numerical ocean model simulations at different resolutions are analyzed although the relevant processes differ patterns in clustering evolution from the deep ocean and the continental shelf bear similarities smaller scale ocean features are associated with stronger surface divergence and the surface material clustering is initially dominated by these features over time the effect of these small scale features becomes bounded as material traverses small scale regions of both positive and negative divergence lower frequency flow phenomena however continue the clustering as a result clustering evolves from initial small scale to larger scale patterns

eocene oligocene boundary biostratigraphic recognition and gradual paleoceanographic change at dsdp site 549 drilling at site 549 located on the goban spur in the northern bay of biscay irish continental margin penetrated an apparently continuous section of upper eocene lower oligocene nannofossil chalks the eocene oligocene boundary as identified by nannofossils does not coincide with that recognized using planktonic foraminifers regardless of which biostratigraphic criteria are used no dramatic nannofloral or planktonic foraminiferal change occurred at the boundary there was a gradual transition from warm water to cool water assemblages through the late eocene with more intense cooling indicated by low diversity assemblages in lower oligocene sediments a bottom water temperature drop occurred in the late eocene through early oligocene as indicated by an 18 o enrichment in benthic foraminifers although some of this enrichment may have been caused by increased ice volume a major benthic foraminiferal faunal change from a nuttallides truempyi dominated assemblage to one dominated by wide and long ranging taxa occurred in the early late eocene no major benthic assemblage changes occurred at the eocene oligocene boundary

palaeoecological analyses of riversleigh s oligo miocene sites implications for oligo miocene climate change in australia during the cenozoic australian environments changed from being dominated by warm and humid rainforests to mainly arid semiarid habitats comparable to those found today northern australia s oligo miocene palaeoenvironment were analysed using mammalian assemblages from the riversleigh world heritage area northwestern queensland limitations of fossil assemblages were minimised using minimum sample richness and taxonomic distinctness analyses because these identify under sampled unrepresentative and taxonomically biased fossil assemblages which can then be removed from the overall analysis cenogram and body mass distribution methodologies were used to help determine the palaeohabitats of seventeen sites from riversleigh that span the late oligocene to early miocene middle miocene and early late miocene the results suggest a change of environment through time with the late oligocene of riversleigh represented by an open forest the early and middle miocene by rainforest and the early late miocene represented by open forest

eddy induced mixed layer shallowing and mixed layer thermocline exchange the effects of eddies on the mixed layer and on the transfer of properties between the mixed layer and thermocline are studied in a high resolution model of an unstable front a spring scenario is considered with a mixed layer maintained against surface warming by wind mixing tilting of the buoyancy gradients by ageostrophic flow is found to shallow the mixed layer over the front giving a mixed layer as shallow as 10 m in some places compared with the equilibrium monin obukhov depth of 30 m away from the front variations of mixed layer depth with time and lateral advection lead to a subduction field that is substantially different from the vertical velocity field vertical velocities associated with the growing instabilities push tongues of a ventilation tracer initially only present within the surface layer down to depths of up to 100 m after 24 days a quarter of this ventilation tracer has been deposited in the thermocline conversely the vertical motions pull nutrients from the thermocline up into the mixed layer giving enhanced surface values along the front in the basin average the geostrophic eddies give vertical eddy diffusivities for a ventilation tracer of o 3 10 10 4m2s 1

uranium and thorium in paleozoic rhyolites of nova scotia the concentrations of u and th in paleozoic rhyolites of nova scotia are closely related to their contents of k the rhyolites were affected by secondary processes including low grade metamorphism that could lead either to enrichment or depletion of these elements the average abundances of u ppm th ppm and k in rhyolites are cambrian 2 69 9 77 and 2 58 respectively silurian 4 50 17 3 and 4 09 respectively and devono carboniferous 4 64 18 3 and 5 67 respectively the depletion of u th and k in cambrian rocks compared with younger paleozoic rhyolites is probably related to secondary processes in silurian and devono carboniferous rhyolites these elements were mainly redistributed during the secondary processes but not removed

regional paleoprecipitation records from the late eocene and oligocene of north america abstract the marine 18o record indicates precipitous cooling or significant expansion of antarctic ice volume across the eocene oligocene epoch boundary at 33 7 ma this climatic step is also found in estimates of decreased paleoprecipitation from paleosols in oregon montana and nebraska but is only a part of a long term decline across the eocene oligocene transition rather than a sudden shift this suggests that climate was driven by a gradual process rather than a single perturbation paleoprecipitation levels stabilized during the oligocene coincident with a stabilization in 18o values possibly indicating a new climatic steady state

eocene oligocene mammalian faunal turnover in the hampshire basin uk calibration to the global time scale and the major cooling event a new high resolution c 1 ma mammalian record in continental eocene oligocene strata in the hampshire basin is used to investigate the nature and timing of the major europe wide mammalian faunal turnover termed the grande coupure whether this was caused by climate change or by competition with taxa dispersing from asia is controversial the mammalian faunas in this record after rarefaction analysis show a sharp reduction in diversity only after the grande coupure improved correlation of nw european successions to global events confirms the grande coupure as earliest oligocene it shows that a c 350 ka hiatus interrupts the hampshire and paris basin sequences prior to the first record of post grande coupure asian taxa hiatus bridging faunas from elsewhere in europe record mainly post grande coupure taxa suggesting that the turnover occurred early in the hiatus minimizing bias to the turnover pattern a previously unrecorded second smaller turnover involving european mammals only immediately precedes the grande coupure in the hampshire basin coinciding with vegetational change this turnover is judged not to represent cooling it is concluded that the grande coupure coincides with the earliest oligocene oi 1 glaciation and that climate change combined with competition to produce the turnover

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

plus ca change a model for stasis and evolution in different environments abstract the plus ca change model proposes that morphological stasis is the usual response to widely fluctuating physical environments on geological timescales until thresholds are reached the lineages that survive in a more changing environment on geological timescales are those that are relatively inert to each environmental twist and turn in contrast to more sensitive lineages in less changing environments generalists in this long term sense are species with properties that enable them to survive throughout wide environmental fluctuations over geological timescales they are thus related to but distinct from ecological eurytopes the model predicts a tendency for continuous gradualistic evolution on land in the tropics and in the deep sea and for more stasis and occasional punctuations in shallow waters and temperate zones as the vast majority of the fossil record comes from dynamic shallow marine environments it is not surprising that many fossil lineages show approximate stasis and occasional punctuations punctuated equilibrium could be being mistakenly perceived as the overwhelming pattern in the history of life because the environments in which gradualism predominates are rarely preserved in the fossil record the evolutionary pattern in a lineage at a single locality is predicted to be stasis when there is greater environmental fluctuation and net directional change and or more widely fluctuating morphologies when environments are more narrowly fluctuating given the quaternary climate upheavals relatively little evolution may be occurring worldwide at present except for evolution induced by humans such a model is bound to have many exceptions it is only about tendency and relative frequency though few case histories are yet known many existing data sets probably contain clues that can be used in testing the model other relevant aspects of perception are also discussed including descriptive biases and evolutionary reversals