oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

macroevolutionary history of the planktic foraminifera planktic foraminifera are an abundant component of deep sea sediment and are critical to geohistorical research primarily because as a biological and geochemical system they are sensitive to coupled bio hydro lithosphere interactions they are also well sampled and studied throughout their evolutionary history here we combine a synoptic global compilation of planktic foraminifera with a stochastic null model of taxonomic turnover to identify statistically significant increases in macroevolutionary rates there are three taxonomic diversifications and two distinct extinctions in the history of the group the well known cretaceous paleogene extinction is of unprecedented magnitude and abruptness and is linked to rapid environmental perturbations associated with bolide impact the eocene oligocene boundary extinction occurs due to a combination of factors related to a major reorganization of the global climate system changes in ocean stratification seawater chemistry and global climate recur as primary

sea surface temperature history of the low latitude western pacific during the last 5 3 million years abstract the late neogene was a time of cryosphere development in the northern hemisphere the present study was carried out to estimate the sea surface temperature sst change during this period based on the quantitative planktonic foraminiferal data of 8 dsdp sites in the western pacific target factor analysis has been applied to the conventional transfer function approach to overcome the no analog conditions caused by evolutionary faunal changes by applying this technique through a combination of time slice and time series studies the sst history of the last 5 3 ma has been reconstructed for the low latitude western pacific although the present data set is close to the statistical limits of factor analysis the clear presence of sensible variations in individual sst time series suggests the feasibility and reliability of this method in paleoceanographic studies the estimated sst curves display the general trend of the temperature fluctuations and reveal three major cool periods in the late neogene i e the early pliocene 4 7 3 5 ma the late pliocene 3 1 2 7 ma and the latest pliocene to early pleistocene 2 2 1 0 ma cool events are reflected in the increase of seasonality and meridional sst gradient in the subtropical area the latest pliocene to early pleistocene cooling is most important in the late neogene climatic evolution it differs from the previous cool events in its irreversible steplike change in sst which established the glacial climate characteristic of the late pleistocene the winter and summer sst decreased by 3 3 5 4 c and 1 0 2 1 c in the subtropics by 0 9 c and 0 6 c in the equatorial region and showed little or no cooling in the tropics moreover this cooling event occurred as a gradual sst decrease during 2 2 1 0 ma at the warmer subtropical sites while that at cooler subtropical site was an abrupt sst drop at 2 2 ma in contrast equatorial and tropical western pacific experienced only minor sst change in the entire late neogene in general subtropics was much more sensitive to climatic forcing than tropics and the cooling events were most extensive in the cooler subtropics the early pliocene cool periods can be correlated to the antarctic ice volume fluctuation and the latest pliocene early pleistocene cooling reflects the climatic evolution during the cryosphere development of the northern hemisphere

the development of antarctic glaciation and the neogene paleoenvironment of the maurice ewing bank abstract a micropaleontologic magnetostratigraphic and sedimentologic analysis of 56 piston cores provides the basis of a geologic study of the late miocene to holocene depositional and erosional history of the intermediate depth maurice ewing bank meb located at the eastern extremity of the falkland malvinas plateau southwest atlantic ocean sedimentation on the meb is controlled presently by the position of the polar front and strong bottom currents beneath the axis of the antarctic circumpolar current acc fluctuations in the position of the polar front and in the intensity of the acc are inferred to have largely controlled deposition on the meb since the initiation of acc flow over the bank in the miocene the sedimentary record of the meb is used to infer the late miocene to holocene oceanographic and climatic conditions in the south atlantic sector of the southern ocean the meb suffered major erosion by intense acc flow during late miocene time which exposed cretaceous miocene sediment near the surface and shaped the present configuration of the bank this erosional event is inferred to have occurred during late miocene to early pliocene time 7 2 4 7 m y b p with the major phase of erosion occurring between middle magnetostratigraphic chron 7 and late chron 6 7 2 6 2 m y b p we suggest that the miocene sedimentary record of the meb and other paleoenvironmental evidence from the circum antarctic region precludes the existence of a west antarctic ice sheet or extensive ice shelves along the antarctic margin prior to the late miocene during the late miocene a west antarctic ice shelf formed in the former west antarctic sea and rapidly thickened until it grounded below sea level to form the west antarctic ice sheet formation of this ice sheet with floating and partially grounded extensions ice shelves in the ross and weddell embayments led to the first major production of true antarctic bottom water formed in a manner similar to today which permanently altered global abyssal circulation late miocene changes in oceanic ccd levels and a permanent shift in the oceanic 13 c 12 c composition may be attributed to this major change in abyssal circulation a decrease in acc velocity during an early pliocene amelioration of climate led to resumption of deposition on the bank from 4 7 to 3 9 m y b p intensification of the acc during the late gilbert and early gauss chrons again resulted in limited deposition and widespread erosion and or non deposition over most of the meb from 4 0 to 3 2 m y b p acc velocity apparently began to wane during the middle of the gauss chron and allowed widespread deposition on the bank during late gauss time 2 9 2 48 m y b p and over more limited areas during earliest matuyama time 2 48 to about 2 2 m y b p during middle to late matuyama time bottom current intensity reached its greatest post miocene level forming a regional disconformity between sediments of about 2 0 and 1 0 m y in age this increased circumpolar circulation and associated erosion is inferred to have peaked during the late matuyama chron 1 2 1 0 m y b p and is approximately the same age as the tentatively dated greatest patagonian glaciation in nearby southern argentina between 1 0 and 0 7 m y b p the bank was blanketed with a coarse erosion resistant layer of ice rafted detritus which armored the older sediment thereby protecting it from major subsequent erosion sedimentation on the meb during the bruhnes chron 720 000 yr b p present was intermittent and finally culminated with the deposition of a veneer of carbonate ooze during or since latest pleistocene time

stable isotopic evidence for latest miocene sea level fall in the mediterranean region the discovery of a marked isochronous decrease of carbon isotope ratio values 0 5 0 8 in marine carbonates at about 6 2 myr has stimulated several speculations regarding the origin of this event1 3 here we report stable isotope studies of planktonic and benthic foraminifera from the late miocene carmona dos hermanos section in southwestern spain which suggest that 1 the carbon shift at 6 2 myr is directly associated with a eustatic sea level lowering recorded in the same section 2 the shift in 13c at 6 2 myr and other times may be related to an increased flux of marine and terrigenous organic matter depleted in 13c and eroded from the continental shelves during sea level lowstands and 3 the sea level fall at 6 2 myr triggered the rapid shift towards hypersaline conditions in the mediterranean well before the deposition of the messinian evaporites

cycles steps and co2 paleoceanography in the united states from 1983 1986 the field of paleoceanography experienced continued growth during the last three years the first international conference on paleoceanography was held in zurich switzerland in july 1983 and a new journal devoted to the topic paleoceanography american geophysical union washington d c began publication in spring 1986 edited by dr james kennett of the university of rhode island nine legs of the r v glomar challenger concentrated upon paleoceanographic topics legs 71 75 in the south atlantic leg 81 in the north atlantic leg 85 in the equatorial pacific leg 86 in the northwest pacific and leg 90 in the southwest pacific several special symposia and conferences resulted in volumes of collected papers dealing with topics such as climate variability hansen and takahashi 1984 the global carbon cycle sundquist and broecker 1985 catastrophes and earth history berggren and van couvering 1984 orbital insolation and periodicity berger et al 1984 and coastal upwelling suess and thiede 1983 some very useful books have been published which summarize existing information on radiolaria anderson 1983 neogene planktonic foraminifera kennett and srinivasan 1983 calcareous nannofossils haq 1983 1984 and biostratigraphy bolli et al 1983

the temporal distribution of evolutionary and migrational events in pelagic systems episodic or continuous the evolutionary and ecological dynamics of origination immigration and extinction emigration patterns of two pelagic groups planktic foraminifera and calcareous nannofossils within two paleoceanographic regions over the past 40 m y are compared with predictions of the turnover pulse hypothesis that speciation extinction and migration are pulsed or episodic and synchronous with change in the physical environment the specific species dynamics examined of the records of 918 species include expected time to extinction origination immigration as a function of geologic time extinction emigration as a function of biologic age and geologic time and the interactive effects of time of origination immigration and geologic time on the probability of extinction emigration overall there is little empirical support for times of evolutionary quiescence or ecological stability rather the dominant pattern is one of continuous rather than episodic evolutionary and ecological activity there is little evidence of synchroneity of response among cohorts or with major change in the physical environment coeval species experience the same time periods differently in terms of the probability of speciation immigration and extinction emigration the empirical patterns support the hypothesis that at this taxonomic and temporal resolution the controlling factors on evolutionary and ecological turnover are more omnipresent than pulsed or episodic

taxonomic evolution of neogene planktonic foraminifera and paleoceanographic relations the taxonomic evolution of neogene 24 ma to present day planktonic foraminiferal species are described using four indices rate of speciation rate of extinction rate of diversification and rate of turnover the evolution of neogene planktonic foraminifera is marked by three principal stages 1 a diversification stage 24 to 16 ma early miocene 2 an equilibrium stage 16 to 5 ma middle and late miocene and 3 a declining stage 5 ma to recent pliocene and quaternary the early miocene diversification was in response to an increase in polar to equatorial thermal gradients and related subdivision of surface water masses during the middle and late miocene the assemblages remained close to their equilibria with relatively low diversification rates the decline in diversity during the pliocene and quaternary probably resulted from adverse effects imposed by both large scale paleoceanographic fluctuations that began about 6 ma and high frequency climatic oscillations related to northern hemisphere glaciations and deglaciations that began at about 2 5 ma bursts of evolutionary activity marked by higher rates of turnover coincided with major paleoceanographic changes average evolutionary rates appear to be similar for tropical transitional and temperate assemblages although the actual numbers of extinctions and speciations are higher in tropical assemblages because of higher standing diversity contemporaneity of turnover peaks in the three climatic regimes indicates global control of paleoceanographic perturbations upon planktonic foraminiferal evolution the observed evolutionary pattern supports the stationary model of stenseth and maynard smith 1984

cenozoic palaeotemperature changes and planktonic foraminiferal speciation the interaction of plate movements and progressive climatic deterioration produced a constantly changing oceanic environment during the cenozoic the destruction of the tethyan seaway and the severing of low latitude oceanographic connections during the past 65 myr ref 1 coupled with the initiation of unrestricted circum antarctic circulation in the middle to late oligocene2 provided the necessary boundary conditions for the development of a global ocean marked by steep latitudinal temperature gradients this is in contrast to the rather mild climate of the mesozoic which was characterized by an ocean with a homogeneous thermal structure and weak latitudinal temperature gradients1 throughout the cenozoic marine plankton were constantly adapting to major changes in the oceanic environment this can be seen for example in the continual development of latitudinal provincialization as a response to polar coolings1 3 here i attempt to evaluate the relationship between palaeotemperature change and planktonic foraminiferal speciation during the past 65 myr

patterns of biotic change in middle jurassic to early cretaceous tethyan radiolaria abstract the rate of taxic turnover of nearly 400 radiolarian species subspecies is analyzed in order to document long term biotic change of plankton during the middle jurassic to early cretaceous aalenian to aptian the pattern and dynamic of diversity change is described using four indices rate of species first and last occurrence rate of diversification and rate of turnover plots of cumulative sampling effort suggest that the analyzed data represent an adequate sample of total standing diversity for most examined stages rates of species first occurrence exceed rates of last occurrence for most of the middle jurassic except for the middle bajocian in contrast the late jurassic was a time of decreasing radiolarian diversity and the kimmeridgian records the lowest rate of diversification it is followed by a dramatic increase in first occurrences near the jurassic cretaceous boundary with as a result the highest rate of diversification recorded in the late tithonian regional radiolarian diversity was stable throughout most of the early cretaceous a stratigraphic permutation test was performed to assess the influence of uneven sampling on the observed pattern of taxic turnover and identified the intervals for which randomly obtained patterns are significantly different from the observed pattern the kimmeridgian and late tithonian events coincide with substantial climate derived perturbations in water cycling nutrient supply and oceanic productivity they point to a negative relationship between radiolarian macroevolution and changes in the state of nutrient availability although further work is needed to refine the temporal resolution of this relationship and to explore ecological aspects of its causal link with respect to radiolarian evolution

how synchronous are neogene marine plankton events an electronic supplement of this material may be obtained on adiskette or anonymous ftp from kosmos agu org login toagu s ftp account using anonymous as the username andguest as the password go to the right directory by typing cdapend type ls to see what files are available type get and thename of the file to get it finally type exit to leave the system paper 94pa01456 how synchronous are neogene marine planktonevents by c spencer cervato h r thierstein d b lazarus andj p beckmann diskette may be ordered from american geophysicalunion 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order we analyzed the synchrony and diachrony of commonly used neogene biostratigraphic events from data published in the initial reports of the deep sea drilling project dsdp and in the proceedings of the ocean drilling program odp on the basis of the combined biostratigraphic and magnetostratigraphic evidence new neogene age models were constructed for 35 globally distributed dsdp and odp holes biostratigraphic events from the four major plankton groups calcareous nannofossils diatoms planktonic foraminifera and radiolarians were compiled from dsdp and odp reports after the elimination of possible sources of error such as stratigraphic hiatuses and reworking of specimens 124 biostratigraphic events that occurred in at least four holes were analyzed in detail for each event a biochronologic age estimate was derived by projection of the depth of the event onto the line of correlation of each hole and from these a global mean age for each event was calculated together with its standard deviation average standard deviations for event ages by fossil group are calcareous nannofossil first appearance datums fads 0 57 m y 21 events calcareous nannofossil last appearance datums lads 0 60 m y 25 events diatom fads 0 57 m y 7 events diatom lads 0 85 m y 14 events planktonic foraminifera fads 0 88 m y 22 events foraminifera lads 0 68 m y 16 events radiolarian fads 0 30 m y 9 events radiolarian lads 0 31 m y 10 events since the average sample spacing in the sites used for this analysis is only 0 185 m y we have examined the data for true patterns of diachrony and for other biases diachrony is more frequent among cosmopolitan than among endemic taxa thus there is a general trade off between the obtainable age precision and the geographic extent of a bioevent precision of age calibrations also decreases with increasing age although some of these features may be due to investigator bias they appear in part to be real phenomena and thus could also provide opportunities for further exploration of important paleobiological processes such as change in environmental gradients through time evolutionary adaptation of species populations and migration due to water mass changes

a paleoceanographic model for the early evolutionary history of planktonic foraminifera the first major radiations of planktonic foraminifera occurred during the mid cretaceous however this period of great diversification was interrupted by two intervals of pronounced paleoceanographic paleoecologic change one during the latest aptian early albian and a second associated with the cenomanian turonian boudary both of these times corresponded with widespread organic carbon burial during intervals commonly referred to as oceanic anoxic events oae 1 and 2 respectively this synthesis focuses on the evolutionary history of aptian early cenomanian planktonic foraminifera and the relationship with oae 1 dynamic paleoceanographic changes controlled the course of planktonic foraminiferal evolution during the mid cretaceous heightened plate tectonic activity a major long term rise of global sea level and an overall increase of global temperatures characterized aptian albian time as proposed here the evolutionary history of aptian early cenomanian planktonic foraminifera was influenced most strongly by changes in the density structure and stability of the upper water column via changes in the sites and rates of water mass production through time and perhaps by subtle changes in oceanic productivity including trophic structure and shifts in productivity centers with rising sea level the creation and growth of epicontinental seas played a major role in regional climate change water mass production and water column structure epicontinental seas were also an important factor in creating vast new niche space and increased biotic diversity for many marine organisms the amplified seasonality and instability of epicontinental seas resulted in habitation of the upper water column by morphologically simple eurytopic planktonic foraminifera several new species of epicontinental sea dwelling planktonic foraminifera appeared during the mid cretaceous however much of the diversification of morphologic form took place in oceanic areas during times of oceanic stability and upper water column stratification during mid to late aptian and late albian time a decline in diversity and return to simple morphotypes occurred when oceanic stability was disrupted and the upper water column was poorly stratified during latest aptian early albian time

the cretaceous tertiary boundary event in the north pacific planktonic foraminiferal results from deep sea drilling project site 577 shatsky rise a detailed micropaleontologic analysis of sediments from deep sea drilling project site 577 from the shatsky rise north pacific was undertaken to describe extinction and radiation patterns of plank tonic foraminifera in a continuous carbonate sequence spanning the cretaceous tertiary k t boundary a 15 m section containing the boundary was closely sampled and contained planktonic foraminiferal assemblages characteristic of the late maastrichtian abathomphalus mayaroensis zone through the danian globorotalia uncinata zone the cretaceous tertiary boundary was placed at the abrupt disappearance of almost all maastrichtian planktonic foraminifera coincident with these extinctions was the presence of a large number of microtektitelike spherules the most important faunal change in the late maastrichtian was an abrupt increase in the relative abundance of the high latitude species hedbergella monmouthensis together with the appearance of diminutive populations of guembelitria cretacea and globigerina eugubina approximately 20 000 years before the boundary these changes are interpreted as indicating a cooling of surface water conditions globigerina eugubina and g cretacea were the only planktonic foraminiferal species to survive the cretaceous tertiary boundary event at this locality the o 18 and c 13 values of g eugubina from below the k t boundary are nearly the same as those from above the boundary but in both cases the o 18 values indicate relatively cooler paleotemperatures than those from other coexisting planktonic foraminiferal species in addition the c 13 values of g eugubina are lighter than those of the other planktonic foraminifera such a relationship might suggest that g eugubina lived in cooler shallow intermediate water masses advected from higher latitudes during a latest maastrichtian cooling episode better preservation of planktonic foraminifera a progressive change in the c 13 of benthic foraminifera and a brief positive excursion in c 13 of the carbonate fine fraction and of planktonic foraminifera within 20 to 30 cm below the k t boundary all suggest important paleoceanographic changes that preceded the extinction event a large population of aberrant g eugubina and eoglobigerina was observed in the earliest danian these forms are characterized by the development of secondary apertures bullae and abnormal final chambers these abnormal morphotypes are considered to be ecophenotypic variants reflecting ecologic stress or instability in the earliest cenozoic marine environment

conceptualizing lateral preferential flow and flow networks and simulating the effects on gauged and ungauged hillslopes 1 one of the greatest challenges in the field of hillslope hydrology is conceptualizing and parameterizing the effects of lateral preferential flow our current physically based and conceptual models often ignore such behavior however for addressing issues of land use change water quality and other predictions where flow amount and components of flow are imperative dominant runoff processes like preferential subsurface flow need to be accounted for in the model structure this paper provides a new approach to formalize the qualitative yet complex explanation of preferential flow into a numerical model structure we base our examples on field studies of the well studied maimai watershed new zealand we then use the model as a learning tool for improved clarity into the old water paradox and reasons for the seemingly contradictory findings of lateral preferential flow of old water where applied line sources of tracer appear very quickly in the stream following application we evaluate the model with multiple criteria including ability to capture flow hydrograph composition and tracer breakthrough we generate output ensembles with different pipe network geometries for model calibration and validation analysis surprisingly the range of runoff response among the ensembles is narrow indicating insensitivity to specific pipe placement our new model structure shows that high transport velocities for artificial line source tracers can be reconciled with the dominance of preevent water during runoff events even when lateral pipe flow dominates response the work suggests overall that preferential flow can be parameterized within a process based model structure via the structured dialog between experimentalist and modeler

planktic foraminiferal diversity as indicator of ocean environments abstract the combination of the number of species simple diversity an information function shannon diversity and a measure of equitability is used to characterize modern ocean environments based on planktic foraminiferal faunas regional environmental conditions can be recognized as deviations from the global latitudinal trend simple diversity number of species offers relatively little resolution itself because it is sensitive to the addition of rare species variable conditions such as the highly productive spring bloom and upwelling are characterized by relatively low diversity and equitability values relatively high diversity and a lesser increase in equitability are found in mixing zones of adjacent water masses in extreme conditions diversity is low whereas equitability is intermediate to high modern patterns can be applied to fossil sections to reconstruct regional paleoceanographic conditions thus relatively low shannon diversity with low equitability in maastrichtian heterohelicid faunas from el kef tunisia is interpreted as indicating variable conditions an increase in simple diversity mostly traces evolution of the heterohelicids as a group which diversified during the maastrichtian the number of species through time is a function of available niches and as such related to oceanic circulation on a global scale therefore when applying modern patterns to fossil sections a distinction has to be made between global diversity trends and regional environmental change the correlation between cenozoic stable isotope record and number of planktic foraminiferal species suggest indeed that simple diversity registers changes in global circulation maximum number of species occurred in the maastrichtian the middle eocene and the early middle miocene in these three instances the maxima are found after the start of a cooling trend and are interpreted as transition periods between two modes of ocean circulation causing the temporary coexistence of old and new species

evolution of mid cretaceous radiolarians in response to oceanic anoxic events in the eastern tethys southern tibet china abstract oceanic anoxic events oaes are well known from their widespread black shale and carbon isotopic excursions in the western and eastern tethys and atlantic ocean however the weakest link in the studies of the oaes is biological evolution sedimentological biostratigraphical and geochemical data from albian to coniacian strata in southern tibet recorded turnover events and fluctuations in diversity of the radiolarian fauna within the eastern tethys during oae 1d and oae 2 abundant radiolarian fossils were obtained from the gyabula formation with 93 species from 43 genera identified and assigned to the mid to upper cretaceous acaeniotyle umbilicata archaeospongoprunum tehamaensis crucella cachensis alievium superbum and dictyomitra formosa zones the association of carbon isotopic excursions black shale and radiolarian turnover indicates extensive changes in the ocean climate system nutrients are made increasing available to the marine plankton through submarine volcanic activity and rising sea level which were a likely cause of radiolarian turnover at or near the oaes active submarine tectonism volcanism leads to the expansion of the hypoxic zone and may cause many deeper dwelling forms to become extinct whereas most of the shallower dwelling radiolarians survive radiolarian evolution thus provides a useful record with which to seek understand relationships between climate paleoceanographic processes and plankton evolution

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

growth increments in gomphotherium tusks and implications for late miocene climate change in north america abstract changes in mammalian faunas in north america during the late miocene are thought to have been caused by the replacement of woodland habitats with grassland or steppe the proposed cause of this habitat shift is the transition from the relatively low seasonality early miocene climate to a more highly seasonal climate regime by the end of the miocene tusks which are highly modified incisor teeth of late miocene gomphotherium mammalia proboscidea were sectioned to document the nature of tusk growth in this genus and to test for patterns of seasonal growth both the dentin and enamel of gomphotherium tusks preserve incremental growth lines dentin has increments on three scales inferred to represent annual first order weekly second order and daily third order periodicities luminance and second order increment thickness profiles were measured on transverse thin sections of tusk dentin viewed at low magnification and the data were examined with bivariate plots and autocorrelation autocorrelograms of luminance data support the consistent identification and measurement of second order increments within and among the tusks sampled profiles of second order increment thickness in three tusks from the barstovian north america land mammal age nalma show no indication of seasonal patterns of growth one tusk from the late clarendonian and one from the early hemphillian nalma have patterns of growth consistent with an increase in seasonality during the late miocene an interpretation supported by autocorrelation of the increment thickness data from these tusks the growth patterns are consistent with the hypothesized changes in north american climate during the late miocene and are suggestive of an increase in aridity and development of a wet season tests of this hypothesis are suggested

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

the evolutionary history of size variation of planktic foraminiferal assemblages in the cenozoic abstract the iterative evolutionary radiation of planktic foraminifers is a well documented macroevolutionary process here we document the accompanying size changes in entire planktic foraminiferal assemblages for the past 70 my and their relationship to paleoenvironmental changes after the size decrease at the cretaceous paleogene k p boundary high latitude assemblages remained consistently small size evolution in low latitudes can be divided into three major phases the first is characterized by dwarfs 65 42 ma the second shows moderate size fluctuations 42 14 ma and in the third phase planktic foraminifers have grown to the unprecedented sizes observed today our analyses of size variability with paleoproxy records indicate that periods of size increase coincided with phases of global cooling eocene and neogene these periods were characterized by enhanced latitudinal and vertical temperature gradients in the oceans and high diversity polytaxy in the paleocene and during the oligocene the observed minor size changes of the largely low diversity oligotaxic assemblages seem to correlate with productivity changes however polytaxy per se was not responsible for larger test sizes

mesozoic calcareous nannofossil evolution relation to paleoceanographic events the taxonomic evolution of jurassic and cretaceous calcareous nannofossil species is described using the following indices species diversity rate of speciation rate of extinction rate of diversification rate of turnover survivorship and species accretion the jurassic prior to the late oxfordian is characterized by positive diversification rates that is rates of speciation exceeded rates of extinction highest rates of diversification occurred in the late lias and early oxfordian during the generally regressive latest jurassic diversification rates remained low and rates of extinctions exceed rates of speciation in the early cretaceous rates of diversification are positive and peak in the early valanginian early aptian and middle albian after which time rates of extinction generally exceed rates of speciation such peaks in rate of evolution coincide with times of increased accumulation of organic carbon in the ocean anoxic events peaks in rates of extinction result in very high rates of turnover during times of major regressions in particular in the tithonian and maastrichtian survivorship analyses for three datum planes 74 5 144 and 160 ma show relatively constant extinction rates with some stepping in the older part they are best explained by a temporally fluctuating abiotic environment causing changes in the probability of extinction species accretion curves are also relatively linear with some indication of changing rates of speciation the coincidences of major changes in evolutionary rates with major paleoceanographic events are indicative of a predominantly abiotic control of nannoplankton evolution relationships of evolutionary rates of calcareous nannoplankton with deep ocean ventilation sea level and ocean fertility indicates that global tectonic processes are the ultimate causes of evolutionary change

cenozoic paleoceanography 1986 an introduction new developments in cenozoic paleoceanography include the application of climate models and atmospheric general circulation models to questions of climate reconstruction the refinement of conceptual models for interpretation of the carbon isotope record in terms of carbon mass balance paleocirculation paleoproductivity and the regional mapping of paleoceanographic events by acoustic stratigraphy sea level change emerges as a master variable to which changes in the ocean environment must be traced in many cases and tests of the onlap offlap paradigm therefore are of crucial importance

danian faunal succession planktonic foraminiferal response to a changing marine environment planktonic foraminiferal evolution following the cretaceous tertiary boundary extinction event is marked by a series of events in which one assemblage is rapidly replaced by another this pattern is characteristic of a highly changing pelagic environment the observed changes in the planktonic foraminifera may be related to long term changes in oceanic productivity that persisted for about the first 2 m y of the danian

miocene stable isotope record a detailed deep pacific ocean study and its paleoclimatic implications deep sea drilling project site 289 in the western equatorial pacific has yielded an extremely detailed record of the carbon and oxygen isotopic changes in the miocene deep ocean the isotopic record reflects major changes in paleoclimate and paleoceanography probably dominated by a major phase of antarctic ice cap growth the transition from a relatively unglaciated world to one similar to today occurred between 16 5 x 10 6 and 13 x 10 6 years before the present with the greatest change occurring between approximately 14 8 x 10 6 and 14 0 x 10 6 years before the present

diversification patterns of planktic foraminifera in the fossil record abstract theories of taxonomic diversification dispute whether global diversity has an upper limit set by the strength of biological interactions or grows in unlimited fashion until catastrophic events reset the system we analyzed a global compendium of fossil planktic foraminifera from the early cretaceous to the present after correcting for temporal differences in sampling effort our results show that their morphological diversity has increased exponentially through time in two different phases the first phase collapsed at the cretaceous paleogene boundary transition the second phase developed through the cenozoic era and declined during the pliocene pleistocene interval a period of time that was dominated by enhanced climatic and oceanographic instability in none of these phases diversity reached an equilibrium level cenozoic faunas evolved faster than those inhabiting cretaceous oceans perhaps as a result of a higher environmental variability our results indicate that planktic foraminifera conform to an exponential diversification model however because catastrophic events have repeatedly reset the level of biological diversity and have kept it below the maximum we cannot confirm whether the level of diversity is potentially unlimited

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

late miocene early pliocene stratigraphy and paleoceanography of the south atlantic and southwest pacific oceans a synthesis the stratigraphy and paleoceanography of the late miocene and early pliocene have been examined at six sites in the south atlantic and southwest pacific oceans deep sea drilling project dsdp sites 284 516a 519 588 and 590 and two piston cores from chain cruise 115 a consistent stratigraphy was developed among sites using graphic correlation which resulted in age models for all sites that are tied to the revised paleomagnetic time scale of berggren et al 1985 applying these chronologies we assessed latitudinal and interocean contrasts in the stratigraphic ranges of late miocene early pliocene planktonic foraminiferal and nanno fossil datums salient stratigraphic results include 1 the last appearance datum lad of globoquadrina dehiscens is a late miocene 6 4 ma event in the subtropics and is not useful for the placement of the miocene pliocene m p boundary in this biogeographic province 2 the first appearance datum fad of globorotalia crassaformis occurred at 5 1 ma in the south atlantic near the m p boundary suggesting that gr crassaformis may have first evolved in the south atlantic and later migrated to other regions 3 in the southwest pacific the fads of gr margaritae 5 97 ma gr puncticulata 5 09 ma and gr crassaformis 4 87 ma are significantly time transgressive between temperate and warm subtropical regions time lags of 1 0 m y were required for these species to adapt to physical and or biotic conditions peripheral to their endemic biogeographic provinces 4 between the subtropics of the south atlantic and southwest pacific many planktonic foraminiferal datums fad of dentogloboquadrina altispira gr cibaoensis gr conomiozea gr margaritae and gq dehiscens and lad of gr cibaoensis markedly depart from the correlation suggested by magnetostratigraphy indicating that these datum levels are unreliable for correlation between these ocean basins 5 in contrast available calcareous nannofossil datum levels fall on or near the paleomagnetic correlation line indicating synchroneity of events within the subtropics 6 biostratigraphic magnetic and 87sr 86sr correlation between sites 588 and 519 and the m p neostratotype at capo rossello sicily suggests that the base of the zanclean stratotype occurs at 5 1 5 0 ma in the lower reversed subchron of the gilbert about 2 3 105 years above the gilbert chron 5 boundary oxygen isotopic results from dsdp sites 284 519 and ch115 piston cores confirm a prolonged benthic 18o increase in the latest miocene between 5 6 and 5 0 ma as originally proposed by shackleton and kennett 1975 at dsdp site 588 the benthic 18o record in the latest miocene is marked by high frequency fluctuations with amplitude variations of 0 5 and a long period wavelength component of 400 000 years maximum 18o values however occurred during the late miocene kapitean stage between 5 5 and 5 1 ma the late miocene 18o changes resulted from mid and high latitude cooling and pulses of ice sheet expansion and contraction glacial events were most intense during the latest miocene kapitean stage and occurred at 5 50 5 35 ma and at 5 10 ma glacial events are estimated to have lowered sea level by 40 to 60 m and contributed to the isolation and desiccation of the mediterranean basin during the late messinian interglacial conditions prevailed at 5 2 ma and between 5 0 and 4 1 ma ihe early pliocene the beginning of the pliocene was marked by changes in many proxy climatic indicators at all sites suggesting a prolonged interval of warm interglacial conditions between 5 0 and 4 1 ma during the earliest pliocene supplementary tables are available with entire article onmicrofiche order from american geophysical union 2000florida avenue n w washington dc 20009 documentp86 001 2 50 payment must accompany order

carbonate time series of the quaternary and late miocene sediments in the pacific ocean a spectral comparison abstract the variance of the quaternary carbonate record of core rc11 209 from the equatorial pacific is almost twice as large as that for the upper miocene of dsdp site 158 from the same region spectral analysis of the carbonate time series shows that the miocene record is dominated by very low frequency components with a concentration of variance near the frequency corresponding to a period of about 400 kyr the quaternary record is also dominated by low frequency components but has in addition concentrations of variance spectral peaks at frequencies corresponding to periods near 100 and 40 kyr cross spectral analysis indicates that both records are coherent with the calculated record of eccentricity of the earth s orbit and that the quaternary record in addition shows coherence with the calculated record of axial tilt these variations in the earth s orbital parameters can then be used to tune the time scales of these two records based on the similarity in the amount of variance in the two records near the 400 kyr period and the observed relationship between carbonate fluctuations and variations in global ice volume as indicated by oxygen isotope measurements it is proposed that the dominant 400 kyr cycle has been associated directly or indirectly with long term fluctuations in the antarctic ice cap since its formation in mid miocene times the major difference in the quaternary carbonate spectrum lies in the marked increase in variance at frequencies associated with the 100 kyr period this increase is thought to be linked directly or indirectly with glacial to interglacial fluctuations of the northern hemisphere ice sheets

the nature and origin of taxonomic diversity gradients in marine bivalves bivalves have been fundamental in developing the understanding of large scale biodiversity patterns in the marine realm a new study based on 29 regional bivalve faunas indicates that both latitudinal and longitudinal gradients are not so regular in form as was once imagined the northern hemisphere latitudinal gradient has a marked step or inflection at 20 30 n and in the southern hemisphere australia forms a distinct diversity hotspot a longitudinal gradient runs between a large tropical high diversity focus in the southern china indonesia australia region and a somewhat smaller one in the panamic caribbean region it is unlikely that the marked asymmetry in both latitudinal and longitudinal gradients can be explained entirely by either the geometric patterns of species ranges in relation to geographical boundaries the mid domain effect or the operation of contemporary or equilibrium factors the role of history must be considered too and in some cases this could involve a timescale of at least 60 ma for example australia has moved progressively northwards throughout the cenozoic era and this seems to have led to the development of a unique assemblage of both tropical and temperate taxa around the continent when australia eventually collided with southeast asia some 15 ma ago three previously distinct tropical marine faunas were brought into close juxtaposition however something else seems to have been involved in order to generate a marked pantropical neogene diversification event in bivalves and other marine invertebrate taxa it is striking how this event coincided with a prolonged interval of global cooling and the suggestion has been made that glacioeustatic cycles may have promoted the formation of a tropical species diversity pump in concert with regular and profound sea level changes new taxa were created in marginal tropical regions and then concentrated in certain core regions these same glacioeustatic cycles may also have served to accentuate the latitudinal limits of many tropical taxa as the knowledge of large scale taxonomic diversity gradients in the marine realm has increased so too has the realization that they are at least the partial products of major historical events

neogene marine climate trends implications for biogeography and evolution of the shallow sea biota a host of data on the biodistribution diversity and taxonomic age patterns of neogene shallow sea faunas can be accommodated within a climatic model which assumes that oceans in the late paleogene were significantly cooler in low latitudes and wanner in high latitudes than at present these climatic assumptions seem compatible with the state of the art in paleotemperature interpretation if the model holds it will effectively eliminate hypotheses of species diversity regulation that depend on the age of climates and will explain the relative youth of genera and families in the tropics

covariance patterns of foraminiferal dgr18o an evaluation of pliocene ice volume changes near 3 2 million years ago oxygen isotope data for a pliocene interval from 3 6 to 2 8 million years ago show a mean increase 0 5 per mil of benthic delta 18 o at about 3 2 million years ago whereas planktic delta 18 o does not increase this lack of covariance indicates that the event at 3 2 million years did not result in a permanent increase in the ice budget of either the northern or the southern hemisphere

abiotic forcing of plankton evolution in the cenozoic we characterize the evolutionary radiation of planktic foraminifera by the test size distributions of entire assemblages in more than 500 cenozoic marine sediment samples including more than 1 million tests calibration of holocene size patterns with environmental parameters and comparisons with cenozoic paleoproxy data show a consistently positive correlation between test size and surface water stratification intensity we infer that the observed macroevolutionary increase in test size of planktic foraminifera through the cenozoic was an adaptive response to intensifying surface water stratification in low latitudes which was driven by polar cooling

glacial interglacial variability in the eastern tropical north pacific oxygen minimum zone recorded by redox sensitive trace metals 1 changes in the intensity of the oxygen minimum zone omz in the eastern tropical north pacific over the past 140 kyr are recorded as enrichments and depletions of redox sensitive metals in sediments of two piston cores one within and one below the modern omz from the continental margin off mazatlan mexico 22 41 n 106 28 w concentrations of al 7 7 0 6 ti 0 37 0 03 fe 3 1 0 25 mn 320 31 ppm and ba 560 82 ppm in core nh15p within the omz at 420 m water depth were relatively constant over the last 110 kyr in contrast concentrations of cd 4 8 2 ppm cu 29 8 9 1 ppm u 9 1 3 7 ppm mo 12 1 5 0 ppm v 138 2 51 9 ppm and re 45 8 25 5 ppb were all at least 30 higher in interglacial stages compared to glacial stages concentrations of al 7 4 0 3 ti 0 35 0 03 fe 3 5 0 4 and mn 385 77 ppm in core nh22p below the omz at 2025 m water depth were comparable to those in core nh15p while concentrations of ba 1662 292 ppm were about a factor of three higher in contrast concentrations of cd 0 9 0 3 ppm u 6 6 0 9 ppm mo 3 2 1 2 ppm v 81 8 10 1 ppm and re 25 4 12 ppb were lower in sediments of comparable age than the concentrations of these same metals in the omz core and the differences in their concentrations over glacial interglacial cycles were less pronounced than those in shallower core comparison of the nonlithogenic fraction of metals in the sediments with their estimated contribution from plankton suggests that organic matter is probably the major source of cu ba and perhaps cd to the sediment whereas the indirect effects of organic carbon and low bottom water oxygen concentrations on sediment redox state appear to be more important controls on the distributions u re mo and v changes in the depth at which re and mo precipitated in the sediments and in the re mo ratio suggest that the redox state of the surface sediment and overlying water at both core depths varied over time re and mo removal depths were shallower and re mo ratios were lower at the omz site than in deeper water suggesting that a more reducing environment prevailed over time at the shallower site although the redox state of the waters and sediment at both sites varied over glacial interglacial cycles the omz likely was never anoxic in the last 140 kyr this variability in redox state could be attributed to changes in regional export productivity changes in ocean circulation or a combination of both processes a paleoproductivity reconstruction from biogenic ba data suggests that glacial productivity was considerable lower than it was during interglacial stages model results suggest that the oxygen penetration depth an indicator of sediment redox state changed less than 1 cm as a result of the change in productivity changes in oxygen penetration depth estimated from re and u removal depths are significantly larger suggesting that changes in ventilation are a more important control on sediment redox state overall trace metal results confirm the tight coupling between ocean circulation marine productivity and global change

oligocene through palaeogene neogene boundary foraminifera of the northern mesohellenic basin macedonia greece biostratigraphy and palaeoecologic implications abstract foraminifera of the oligocene and early miocene siliciclastic units from the northern part of the mesohellenic basin macedonia northern greece provide good biostratigraphic potential taxa identified from a number of sections cropping out in the study area indicate that these deposits fan in zones p20 upper part p21 p22 and most of zone n4 of blow s zonal scheme the occurrence within the lowest part of the pendalofos formation of abundant globigerinoides primordius together with other earliest miocene planktonics defines the base of the miocene although a remarkable planktonic foraminiferal turnover occurred close to the palaeogene neogene boundary the benthic populations do not show any clear change except in relation to palaeoecologic conditioning analysis of benthic foraminifera led to the definition of a palaeodepth curve indicating that the deposition during the late oligocene and early miocene occurred in a middle to upper mostly bathyal and outer neritic conditions the distribution of selected benthic foraminifera is compared with sedimentologically derived depositional environments the correlation between the major global unconformities predicted by the exxon coastal onlap chart and the mesohellenic succession is based on the joint use of biochronologic and biostratigraphic palaeoecologic tools

tectonic subsidence flexure and global changes of sea level tectonic models for the evolution of passive continental margins predict that following rifting sediments should progressively onlap basement at the edge of a margin as the lithosphere cools and increases its flexural rigidity with age the pattern of modelled onlap is strikingly similar to that used by vail and colleagues to estimate sea level rise through geological time this similarity suggests that major portions of stratigraphical sequences at margins may have a tectonic rather than eustatic control the patterns of onlap used by vail and colleagues may be widespread however because several widely separated passive margins rifted at similar times but they are unlikely to be worldwide

cenozoic glaciation in the southern hemisphere with the end of glaciation in gondwana in early permian time a prolonged interval began when the earth was without ice sheets though not necessarily free of mountain glaciers not until sometime during the tertiary era did ice sheets build up once more first in antarctica and later in the northern hemisphere the fundamental cause of the cooling that led to the formation of the antarctic ice sheet and eventually to major glaciation in lower latitudes is generally held to have been the increasing thermal isolation of antarctica as australia and later south america separated from it allowing zonal oceanic circulation to develop rifting between australia and antarctica began between 1 10 and 90 m y ago cande mutter 1982 but not until much later probably sometime between 30 and 25 m y ago had it progressed far enough for deep circulation to begin as the south tasman rise cleared north victoria land kennett et a1 1974 kennett 1977 weissel et ai 1977 however antarctica did not reach its present high level of thermal isolation until south america had separated from it enabling the antarctic circumpolar current to become established savin et ai 1975 according to barker burrell 1977 1982 coherent spreading between the antarctic peninsula and tierra del fuego started about 29 m y ago and deep circulation began 23 5 2 5 m y ago thereafter increasing in volume the initial ice fields and ice caps that later expanded to become the

miocene benthic foraminiferal isotope records a synthesis abstract 18 o 16 o and 13 c 12 c ratios of miocene benthic foraminifera from a number of atlantic pacific and indian ocean dsdp sites 71 77b 206 208 238 279 289 296 329 357 and 366a have been compiled these provide a rather detailed history of miocene deep water especially in the pacific ocean bottom water temperatures rose during the early miocene and then declined rapidly during the middle miocene this decline was accompanied by an increase in antarctic glaciation late miocene bottom temperatures and antarctic ice volumes are inferred to be similar to today s but exhibited some fluctuation the early miocene ocean was less thermally stratified at intermediate and abyssal depths while the late miocene deep ocean had a thermal structure generally similar to the modern ocean foraminiferal carbon isotope ratios at most of the sites varied quasi sympathetically throughout the miocene these variations must reflect comparable variations in the mean 13 c 12 c of marine hco 3 however the causes of such variations are not yet clear

causes of antarctic glaciation in the cenozoic the causes of antarctic glaciation are analyzed by means of numeral experiments based on the three dimensional thermodynamic model of a large ice sheet refrigeration of the climate between the eocene and the oligocene was due to the opening of the passage south of australia and to the formation of the south ring stream calculations have shown that this led to the development of the east antarctic ice sheet which might have existed in spite of relatively high temperatures of the surrounding ocean air a new cooling of the climate in the middle miocene is connected with the fact that the south ring stream found its way through the drake passage glaciers spreading on to the western antarctic between miocene and pliocene glaciation of the south polar regions was at its maximum due to the regression of the world ocean in quaternary time sea level was lowering due to the glaciation of the northern hemisphere which resulted in glacier growth in the antarctic the anticipated warming of the climate due to the activity of man is not likely to bring about any considerable change in the size of the east antarctic ice sheet

slip weakening models of the 2011 tohoku oki earthquake and constraints on stress drop and fracture energy we present 2d dynamic rupture models of the 2011 tohoku oki earthquake based on linear slip weakening friction we use different types of available observations to constrain our model parameters the distribution of stress drop is determined by the final slip distribution from slip inversions as three groups of along dip slip distribution are suggested by different slip inversions we present three slip weakening models in each model we assume uniform critical slip distance eastward from the hypocenter but several asperities with smaller critical slip distance westward from the hypocenter the values of critical slip distance are constrained by the ratio of deep to shallow high frequency slip rate power inferred from back projection source imaging our slip weakening models are consistent with the final slip slip rate rupture velocity and high frequency power ratio inferred for this earthquake the average static stress drop calculated from the models is in the range of 4 5 7 mpa though large spatial variations of static stress drop exist to prevent high frequency radiation in the region eastward from the hypocenter the fracture energy needed there is in the order of 10 mj m2 and the average up dip rupture speed cannot exceed 2 km s the radiation efficiency calculated from our models is higher than that inferred from seismic data suggesting the role of additional dissipation processes we find that the structure of the subduction wedge contributes significantly to the up dip rupture propagation and the resulting large slip at shallow depth

isolation extinction and migration within late pliocene populations of the planktonic foraminiferal lineage globorotalia globoconella in the north atlantic abstract quantitative records of globorotalia puncticulata and globorotalia inflata the last two members of the globorotalia globoconella lineage obtained from north atlantic sediments collected at dsdp site 552 odp site 659 and odp site 665 are used to examine fluctuations in the biogeographic distribution of these species in the late pliocene between 3 and 2 ma abundance data indicate that prior to the expansion of northern hemisphere glaciation at about 2 5 ma gr puncticulata was an important component of the planktonic foraminiferal fauna and had a geographic distribution ranging from 2 n to at least 56 n in the north atlantic a previously undescribed 6 chambered variant of gr puncticulata is found at both sites 659 and 665 the stratigraphic distribution of this morphotype is restricted first occurring at 2 9 ma and then disappearing when glacial intensity increased at 2 75 ma isotope stage 110 similar declines in gr puncticulata abundances occurred during glacial isotope stages 102 100 and 98 immediately prior to the extinction of gr puncticulata during glacial isotope stage 96 it appears that this extinction event was latitudinally diachronous within the north atlantic occurring earliest in the north at site 552 2 453 ma then at site 659 2 443 ma and later still in the site 665 equatorial record 2 438 ma at site 665 the first record of gr inflata occurs during glacial isotope stage 94 2 416 ma shortly after the extinction of gr puncticulata in the mid latitude north atlantic there was a 340 000 year period following the disappearance of gr puncticulata when the globoconella lineage was absent the gr inflata gap the gr inflata population found in the equatorial atlantic must therefore have been introduced from the south atlantic probably by the south equatorial current faunal records from sites 552 and 659 show that it was not until glacial isotope stage 78 2 10 ma that gr inflata became widely established in the north atlantic prior to this large scale migration event there were two limited colonisation events during glacial isotope stages 86 and 82 when gr inflata populations reached as far as site 659 in the eastern north atlantic these incursions are believed to be reflect the entrainment of gr inflata within south atlantic central water and the northward subsurface transport of individuals to the coastal upwelling zone off northwest africa it seems likely that the same mechanism was responsible for the re establishment of the globoconella lineage in the north atlantic at 2 10 ma but in this instance additional factors such as enhanced glacial circulation patterns and ecological changes within planktonic foraminiferal faunas resulted in the successful expansion of gr inflata across the north atlantic and the mediterranean

late miocene earliest pliocene glaciation in southern argentina implications for global ice sheet history abstract in south america at latitude 47 s till was deposited sometime between 7 m y and 4 6 m y ago at a time when the local climate was colder than today s during this same interval glaciers extended to sea level in southeast alaska and widespread cooling of the ocean surface in middle latitudes worldwide marine regression and change in the oxygen isotopic composition of ocean water occurred from the last three events major late miocene expansion of the antarctic ice sheet has been inferred on the assumption that the history of north atlantic ice rafting precludes the existence of northern hemisphere ice sheets until 3 m y ago this is disputed first because precipitation in antarctica would probably have decreased at temperatures below today s second because the antarctic ice sheet cannot expand appreciably until buildup of northern hemisphere ice sheets has lowered sea level third because virtually no late miocene sediments are present at the labrador sea dsdp sites that are critical to the reconstruction of north atlantic ice rafting history and fourth because the scale of late miocene glaciation in alaska is at least permissive for simultaneous buildup of ice at similar latitudes further east if global ice sheet volume at the end of the miocene was greater than it is today by an amount that would have lowered sea level by several tens of meters the excess ice did not accumulate in antarctica but in the northern hemisphere chiefly in north america away from the atlantic coast

obliquity and long eccentricity pacing of the middle miocene climate transition 1 the middle miocene east antarctic ice sheet expansion eaie which is indicated by an abrupt 1 increase in global benthic foraminiferal 18o at 13 8 ma marks the middle miocene climate transition mmct and has been related to astronomically modulated changes in the global carbon cycle here we present high resolution 3 4 kyr benthic foraminiferal 18o and 13c records from iodp site u1337 in the central equatorial pacific which spans the period 12 2 15 8 ma the isotopic records clearly demonstrate significant imprints from periodic variations in the earth s orbital parameters particularly the obliquity 40 kyr and the long eccentricity 400 kyr cycles while the benthic 18o and 13c exhibit nearly identical amplitudes for glacial interglacial cycles from 15 8 to 12 2 ma the long term trends in the benthic 18o and 13c had started to reverse after the beginning of the eaie within the 400 kyr band the benthic 18o and 13c displays a constant phase relationship between 15 8 and 12 2 ma at the 41 kyr band however a phase reversal reaching 180 between 18o and 13c occurs from 13 8 ma to 14 0 ma during the period of the eaie a similar phase relationship of benthic foraminiferal 18o and 13c at the 400 kyr band and the 41 kyr band is also observed at odp site 1146 from the northern south china sea this phase jump occurs when the long term trends in 18o and 13c split suggesting a decoupling of the global ice volume and ocean carbon reservoir changes during the middle miocene

miocene equatorial and southwest pacific paleoceanography from stable isotope evidence abstract stable isotope results from seven miocene deep sea drilling projects in the equatorial and southwest pacific ocean previously correlated using carbon isotope stratigraphy have been examined discussed and interpreted in terms of the development of the miocene pacific ocean the most obvious features of the benthonic foraminiferal stable isotopic records are a major increase in 18o 1 0 during the middle miocene a series of long term oscillations 2 3 my of amplitude 0 5 0 75 and a decrease in 13c values 0 5 1 0 during the latest miocene planktonic foraminiferal 18o records show different trends for high and low latitude regions in the equatorial pacific planktonic 18o values actually decrease during the miocene whereas in the higher southern latitudes planktonic 18o values become more positive in response to cooling surface waters planktonic 13c records show opposite trends to 18o with the high latitude values becoming more negative relative to the tropical regions the development of the miocene pacific ocean in terms of its vertical and horizontal thermal structure and isotopic composition is well illustrated by examining changes in the isotopic difference between planktonic and benthonic foraminifera 18ob p benthonic planktonic is a measure of the thermal structure of the water column 18oph pl high latitude low latitude planktonic values is a measure of the latitudinal temperature gradient 13cb p is an indirect measure of nutrient concentrations in the water column and 13cph pl measures differences in surface water nutrient concentrations between high and low latitude 18ob p increases during the miocene with the greatest increase occurring in the middel miocene at about 14 ma by the latest miocene the isotopic gradient at site 289 in the equatorial pacific approaches the present day isotopic gradient about 4 5 an increase in 18oph pl during the miocene suggests that the latitudinal temperature gradient increased by about 6 c to a value of 12 c in the latest miocene between sites 289 equator and 281 subantarctic 13cb p and 13cph pl values are relatively constant through the early miocene but begin to increase during the middle miocene bottom water 13c values respond similarly at all sites but surface water 13c values exhibit different trends because higher latitude values begin to decrease this decrease perhaps suggests that phosphate concentrations may have increased due to increased upwelling as the circum antarctic circulation system evolved its present day characteristics the isotopic data compiled in this paper suggest that the southwest pacific was responding uniformly to some global or at least pacific wide control during the early miocene in the middle miocene the response became more complex as the low and high latitudes began to show independent trends the changes in the thermal vertical and latitudinal structure probably occurred in respons to the build up of the east antarctic ice sheet intensification of bottom water circulation and an increase in zonal circulation in surface waters in the southern hemisphere the changes in 13c vertical and latitudinal gradients are due to some complex interaction of sea level continental hypsometry climate and biological processes coupled with oceanic circulation changes a strong correlation between estimated sea level changes and 13c values suggests that transgressions and regressions play a critical role in controlling the flux of oxidized organic carbon enriched in12c from the continental shelves and epicontinental seas to the open ocean

ocean basin and depth variability of oxygen isotopes in cenozoic benthic foraminifera abstract one of the longest most detailed quantitative records of oceanographic change in the cenozoic is that provided by oxygen isotope measurements made on the tests of foraminifera as indicated by measurements on benthic foraminifera the deep waters of the world ocean have undergone an overall cooling of about 10 c in the cenozoic this change has been neither monotonic nor gradual rather it is evidenced by a few relatively rapid increases in the 13 o content of the benthic shells these steps in the isotopic record have been associated with major evolutionary changes in the mean state of the deep ocean the variance around this mean state has also changed through the cenozoic from relatively high variance in the middle eocene the oceans showed low variance in the late eocene and oligocene in the miocene the variance of the isotopic measurement again increased reaching a maximum of short duration in the middle miocene this maximum as well as that which occurred during the late pliocene and quaternary may be attributable to fluctuations in the isotopic composition of the oceans caused by growth and decay of large ice sheets in the late miocene the benthic oxygen isotopes in atlantic sites less than 3000 m deep have a higher variance than sites at similar depths in the pacific and indian oceans it is thought that this high variance results from long term changes in the importance of the cool and salty north atlantic deep water relative to that of the warmer and less saline antarctic intermediate water at atlantic sites between 1000 m and 3000 m water depth such significant differences in benthic isotopic variance between the ocean basins have been demonstrated only in post middle miocene intervals