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

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

the progressive intensification of northern hemisphere glaciation as seen from the north pacific ocean drilling project odp site 882 50 22 n 167 36 e provides the first high resolution grape density magnetic susceptibility carbonate opal and foraminifera planktonic and benthic stable isotopes records between 3 2 and 2 4 ma in the northwest pacific we observed a dramatic increase in ice rafting debris at site 882 at 2 75 ma which is coeval with that found in the norwegian sea suggesting that the eurasian arctic and northeast asia were significantly glaciated from 2 75 ma onwards prior to 2 75 ma planktonic foraminifera 18o records indicate a warming or freshening trend of 4 c or 2 over 80 ka if this is interpreted as a warm pre glacial pliocene north pacific it may have provided the additional moisture required to initially build up the northern hemisphere continental ice sheet the dramatic drop in sea surface temperatures sst 7 5 c at 2 75 ma ended this suggested period of enhanced sst and thus the proposed moisture pump moreover at 2 79 and 2 73 ma opal mass accumulation rates mar decrease in two steps by five fold and is accompanied by a more gradual long term decrease in caco3 mars evidence from the southern ocean odp site 704 indicates that just prior to 2 6 ma there is a massive increase in opal mars the opposite to what is found in the north pacific this indicates that the intensification of northern hemisphere glaciation was accompanied by a major reorganisation of global oceanic chemical budget possibly caused by changes in deep ocean circulation the initiation of northern hemisphere glaciation occurred in the late miocene with a significant build up of ice on southern greenland however the progressive intensification did not occur until 3 5 3 ma when the greenland ice sheet expanded to include northern greenland following this stage we suggest that the eurasian arctic and northeast asia glaciated at 2 75 ma approximately 100 ka before the glaciation of alaska 2 65 ma and 200 ka before the glaciation of the north east american continent 2 54 ma

pliocene pleistocene vegetational and climatic evolution of the south central mediterranean abstract the vegetational history of the south central mediterranean clearly reflects the major global climatic changes of the last four million years a mediterranean type climate characterized by strong seasonality and a dry summer may have existed in this region during the early pliocene a short term climatic cooling at approximately 3 2 ma resulted in the temporary establishment of a humidity demanding flora the onset of major northern hemisphere glaciation at approximately 2 4 ma initiated an alternation between humid glacial and dry interglacial conditions vegetational differences between this region and the north west mediterranean indicate that distinct latitudinal climatic gradients probably existed in the mediterranean during the pliocene early pleistocene

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

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

variations in the fine scale composition of a central pacific ferromanganese crust paleoceanographic implications a 47 to 60 mm thick fe mn crust from horizon guyot water depth 1800 1780 m central pacific was used to evaluate the potential of crusts as recorders of neogene paleoceanographic and paleoclimatic conditions the chemical composition was determined by microprobe for 16 elements from a polished thin section three analyses were made per millimeter and averaged to give the composition of each millimeter the age of the crust was determined by measuring the strontium isotope composition of the crust and comparing it with the tertiary seawater curve the crust represents 18 5 m y of growth of fe and mn oxyhydroxides the crust is composed of alternating botryoidal and laminated layers the botryoidal layers formed during the same time intervals that widespread neogene deep sea hiatuses were forming in bottom sediments the botryoidal layers represent growth during times of intensified deepwater flow whereas the laminated intervals represent more quiescent conditions the correspondence between the botryoidal layers and the neogene hiatuses is so strong that we were able to choose a variable growth rate model over a constant growth rate model for the crust chemical changes in the crust take two forms the first is represented by broad changes in the composition defined chiefly by fourth order polynomial fits to the chemical profiles of each element with depth in the crust the second is high frequency changes in composition the broader changes occurred primarily at about 15 11 5 7 4 6 4 5 2 and 4 6 ma which may correlate with major changes in paleoceanographic circulation and development of ice caps at the poles the periods of the high frequency changes may reflect climatic changes that resulted from orbital forcing these high frequency changes may correspond to the high order eccentricity periods of 3 47 2 04 and 1 31 m y

late pliocene onset of glaciation ice rafting and diatom stratigraphy of north pacific dsdp cores abstract the revised diatom biostratigraphy for the north pacific allows the timing of ice rafting as recorded in deep sea drilling project cores to be determined significant ice rafting began at the time of the matuyama gauss reversal boundary about 2 48 ma other bio and lithostratigraphic data from the pacific atlantic and arctic oceans and the black sea all indicate that northern hemispherical cooling and the accumulation of continental ice began at 2 4 2 5 ma we interpret all these data to indicate northern hemisphere ice cap formation at that time if so the closing of the isthmus of panama approximately 3 2 m y ago was not the immediate cause of the plio pleistocene glaciations

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

pliocene pleistocene stable isotope and paleoceanographic changes in the northern south china sea abstract based on the stable isotopic analysis of planktonic and benthic foraminifers from ocean drilling program core 1148 of the northern south china sea scs pliocene pleistocene isotope stratigraphy and events have been reconstructed the benthic foraminiferal 18o record shows that the pacific intermediate water had a greater influence upon the scs or the pacific deep water above 2600 m was warmer before 3 2 ma than at present after that the benthic 18o conspicuously increased during the 3 2 2 5 ma period in correspondence to the formation of the northern hemisphere ice sheet whereas the planktonic 18o signal suggests a stepwise overall decrease of sea surface temperature during the 2 2 0 9 ma period compared to the equatorial pacific records the decrease in planktonic globigerinoides ruber 13c during the 3 2 2 2 ma period is particularly striking suggesting that fertility of surface water increased noticeably according to the modern 13c distribution of g ruber in the northern scs it is inferred that the east asian winter monsoon strengthened during this interval afterwards there were several conspicuous decreases of g ruber 13c at 1 7 1 3 0 9 0 45 and 0 15 ma bp that is about every 0 4 ma suggesting that the east asian winter monsoon became episodically stronger this is confirmed by changes in relative abundance of planktonic foraminifer species neogloboquadrina dutertrei a typical east asian winter monsoon proxy the deep water 13c of the scs is close to that of the pacific but lighter than that of the atlantic implying that the pattern of deep water originating mainly from the atlantic and through the pacific entering the scs existed at least since the early pliocene after 1 4 ma the benthic 13c signal decreased conspicuously but with a periodicity of 100 ka suggesting that the deep water ventilation of the scs was reduced probably corresponding to a decrease of the north atlantic deep water and or further isolation of the scs deep basin from the pacific during glaciations

a δ13c record of upper north atlantic deep water during the past 2 6 million years benthic foraminiferal 813c data from site 502 in the caribbean sea sill depth 1800 m indicate that throughout the past 2 6 m y glacial 8 3c values in the middepth atlantic were higher during glaciations than interglaciations this is interpreted as indicating a greater proportion of upper north atlantic deep water unadw relative to southern source waters during glaciations the contribution of unadw during interglaciations to the middepth atlantic remained approximately constant and the contribution during glaciations may have been as much as 10 higher in the late pleistocene than in the late pliocene this small increase is in striking contrast to the much larger decrease in glacial lower north atlantic deep water lnadw contribution relative to southern sources from about 80 to about 20 that occurred over the past 2 6 m y glacial intensification over the past 2 6 m y was probably coupled with a decrease in northward heat transport by the upper limb of the north atlantic circulation cell as was previously suggested on the basis of a lnadw record alone late pleistocene 1 ma present 813c values in the caribbean sea were approximately 0 2 0 higher than they were from 2 6 to 2 0 ma the 813c rise is not due to an increase in the mean ocean 8 3c value nor can it be entirely attributed to an increase in the proportion of high 8 3c source waters an increase in the 813c value of the surface source waters must have contributed to the 8 3c rise

nonlinear response of pliocene climate to orbital forcing evidence from the eastern equatorial pacific a high resolution radiolarian record from the eastern equatorial pacific is used to examine paleoceanographic events during the pliocene from 1 8 to 4 9 ma these data provide a means to evaluate the response of the equatorial pacific to the onset of northern hemisphere glaciation near 2 47 ma and to the closure of the isthmus of panama near 3 2 ma responses are recorded both as long term trends and as variations within the milankovitch band 104 to 105 years radiolarian based sea surface temperature sst estimates indicate a mean cooling from lower to upper pliocene but no significant changes occur near the onset of northern hemisphere glaciation and no abrupt changes are observed before or after the closure of the isthmus spectral and cross spectral analyses of this sst time series indicate concentrations of variance within the precession 23 kyr and obliquity 41 kyr bands in several but not all time intervals variance is commonly concentrated at lower frequencies cross spectral analysis of sst time series and calculated orbital variations indicates that the sst record is not coherent with and therefore not linearly related to orbital variations detailed time series analysis of the sst and 18o time series indicates the absence of a direct linear relationship but rather the presence of a strongly nonlinear relationship between pliocene climatic variables and earth s orbit high coherence is seen between the amplitude of the 23 kyr component of sst and the amplitude modulation of precession the amplitude modulation of the 41 kyr component of the sst record is dissimilar to the amplitude modulation of obliquity but is extremely similar to and coherent with the amplitude of the 23 kyr component of sst the amplitude modulations of sst and 18o at a range of frequency bands have the same features features that roughly follow the modulation of precession this suggests a strongly nonlinear response of equatorial pacific sst and planktonic 18o to orbital forcing in the pliocene such a response extending over a number of frequency bands has not previously been seen in a paleoclimatic data set but may be consistent with proposed models describing paleoclimatic variability although the reasons for this response are still unclear it is evident that strong nonlinearities in climate are present during this time

hydroclimate change in subtropical south africa during the mid piacenzian warm period abstract the mid piacenzian warm period mpwp 3 264 3 025 ma of the pliocene epoch has been proposed as an analog for future climate scenarios disagreement between the paleoenvironmental reconstruction and model simulations of the climate in subtropical regions for this period suggests that more investigation of the subtropical climate variability of the mpwp is needed this study presents pollen microcharcoal and benthic foraminifera oxygen isotope records generated from marine sediment cores of international ocean discovery program iodp exp 361 site u1479 from the cape basin offshore of south africa for the period between 3 337 and 2 875 ma with an average sample resolution of 3 ka this record represents the highest resolution record of mpwp vegetation change from the region our results indicate that the vegetation during the mpwp was dominated by fynbos species rich heathy vegetation in the cape floristic region with variable proportions of ericaceae moreover the development of the afrotemperate forest tall multilayered indigenous forests in south africa reflects shifts in the amounts of precipitation between winter and summer in the year round rainfall zone the vegetation variation is probably influenced by the latitudinal insolation gradient in response to precession forcing several glacials depicted by the benthic foraminifera oxygen isotope record were characterized by lower percentage values of restionaceae higher percentage values of ericoid fynbos and afrotemperate forest these events correspond well with cooler se atlantic sea surface temperatures driven by interactions of both atmospheric and oceanographic processes the cooler sea surface temperatures attributed to antarctic ice sheet expansion reduced agulhas leakage heat and salt transfer from the indian ocean to the atlantic ocean and or intensified southern benguela upwelling resulted in less precipitation in the winter rainfall zone of south africa

a 3 3 ma impact in argentina and possible consequences enigmatic glassy materials escorias and red bricklike materials tierras cocidas occur at a restricted stratigraphic level the top of the chapadmalal formation materials from one locality near mar del plata are attributed to a mid pliocene impact event with a radiometric and magnetostratigraphic age of 3 3 million years ago ma an extinction of endemic fauna including the glyptodonts and flightless cariamid birds correlates with the unit containing the impact glasses moreover the age of the glasses is coincident within dating uncertainties with a pulselike change in the oxygen isotope marine record in the atlantic and pacific oceans just before the late pliocene deterioration of the climate

stratigraphy and depositional history of the pliocene bianco section calabria southern italy abstract an integrated micropaleontological and geochemical study was carried out on the pliocene age bianco section located in calabria southern italy this section is somewhat unique for the pliocene of the mediterranean region in that it contains abundant calcareous and siliceous microfossils based on the biostratigraphic findings it ranges in age from approximately 3 7 3 0 ma the bianco section is composed of marly mudstones intercalated with diatomites with the diatomites being particularly common in the upper 50 m of the section above 3 1 ma the diatomites contain an abundant benthic foraminiferal assemblage and have a low organic carbon content indicating that bottom waters were fairly well oxygenated during their deposition faunal and floral indicators suggest a cooling of surface waters in this region at 3 1 ma the diatom assemblages within the bianco diatomites are very similar to those living in the gulf of california suggesting an upwelling origin for these silica rich units a model is proposed which attributes diatomite formation to upwelling induced by climatically controlled changes in local hydrography

pliocene pleistocene oxygen isotope record site 586 ontong java plateau abstract oceanographic changes in the western equatorial pacific during the past 6 ma are inferred from oxygen isotopic analyses of planktic and benthic foraminifera from ontong java plateau dsdp site 586 the taxa areglobigerinoides sacculifer pulleniatina cibicidoides wuellerstorfi andoridorsalis umbonatus cooling and ice buildup are indicated by an18o enrichment of 0 3 in the planktic species near 3 4 ma this shift apparently is compensated in the benthic data by a warming of the deep waters by between 1 and 2 c we suggest that the dominant source of upper deep water supply to the pacific changed from antarctic to north atlantic at that time the north atlantic derived water being warmer near 2 8 ma approximately the planktic foraminifera again record an enrichment in18o 18o 0 25 we suggest ice buildup in the northern hemisphere as the cause because of subsequent sharp increase in fluctuations of the 18o signal that is instability the enrichment is magnified in the benthic foraminifera 18o 0 5 by a cooling of the deep water by 1 5 at the time presumably signalling a glacial type reduction of north atlantic deep water nadw production episodic divergence between the signals ofg sacculifer andpulleniatina in the pleistocene apparently reflects periods of increased upwelling in the western equatorial pacific the amplitude of ice volume fluctuations cannot be reconstructed from 18o data alone unless there are constraints on temperature variations the increase in amplitude of fluctuation of the benthic and planktic signals during the pleistocene may be attributed either to an increase in maximum ice volume or to an increase in the fractionation of continental ice or a combination of both causes

precise dielectric profiling of ice cores a new device with improved guarding and its theory dielectric profiling dep a capacitive method for measuring an ice core s electrical conductivity and permittivity has been in use for several years we have built an improved dep instrument with a modified guarded electrode geometry whose capacitance can be determined from potential theory the new instrument can measure an ice core s conductivity and permittivity to within a few per cent error a high enough accuracy to infer its density using well known models

pliocene variations in the position of the antarctic convergence in the southwest atlantic middle to late pliocene 4 1 1 9 ma variations in the positions of surface water masses and migrations of the polar front in the southwest atlantic are inferred from a factor analysis of radiolarian assemblages from dsdp site 514 faunal results suggest that surface water masses underwent progressive cooling as the polar front zone pfz advanced northward during the latest gilbert to late gauss chron the late gilbert chron 4 12 3 86 ma was the waning phase of a mid gilbert warm interval northern subantarctic surface water prevailed between 4 12 and 3 97 ma indicative of surface water temperatures warmer than those during the succeeding pliocene a long term sea surface cooling trend began between 3 97 and 3 86 ma which moved the pfz northward and closer to site 514 bringing cooler southern subantarctic surface waters to the site this movement northward of cooler surface waters is inferred to be related to the initial growth of sea ice and ice shelves throughout regions of west antarctica which were deglaciated or unglaciated during the prior warming interval of the gilbert chron a major late gilbert early gauss chron increase in the production of antarctic bottom water aabw resulted in an erosional or nondepositional hiatus at site 514 spanning 3 86 to 3 18 ma increased aabw activity at this time is linked to continued growth of expansive ice shelves and sea ice in the west antarctic region in the east antarctic margin and possibly in the marine embayments of east antarctica decreased aabw production led to a 3 2 ma resumption of sedimentation at site 514 and elsewhere in the southern ocean antarctic surface water assemblages above the hiatus 3 18 3 16 ma suggest that the pfz first passed over site 514 during the 3 86 3 18 ma interval of the hiatus following this initial invasion of antarctic surface waters between 3 16 and 2 94 ma the pfz retreated to a position near or south of the site this slight retreat of the pfz with a corresponding decrease in aabw activity is possibly related to a significant reduction in the area of shelf and sea ice as grounded ice expanded in the west antarctic region we interpret the widespread global enrichment of 18o at approximately 3 2 ma to be partially related to a cooling of surface waters the production of cooler bottom waters and an expansion of west antarctic ice volume associated with its grounding phase between 3 5 and 2 7 ma based on surface water mass migrations at site 514 the west antarctic ice volume increased significantly slightly prior to or at approximately 3 2 ma decreased between 3 14 and 2 7 ma and then increased by 2 67 ma to a more stable configuration with a volume at least as great as that at 3 2 ma during the late gauss 2 94 2 47 ma four northward advances of the pfz led to the migration of antarctic surface waters over the site by 2 67 ma and continued dominance of antarctic surface water through the remainder of the pliocene we suggest that this permanent change from subantarctic to antarctic surface water mass dominance was linked indirectly to the initial growth of northern hemisphere ice and a reduction of sea level we propose a model of simultaneous northern and southern hemisphere ice volume growth induced by interhemisphere positive feedback which is responsible for the major late gauss advance of antarctic surface waters and the global enrichment of 18o at 2 5 ma

on climate and abyssal circulation in the atlantic ocean during late pliocene marine isotope stage m2 3 3 million years ago abstract marine isotope stage mis m2 3 3 ma is an isolated cold stage punctuating the benthic oxygen isotope 18o stratigraphy of the warm piacenzian interval of the late pliocene epoch the prominent 0 65 18o increase that defines mis m2 has prompted debate over the extent to which it signals an early prelude to the rhythmic extensive glaciations of the northern hemisphere that characterise the quaternary and raised questions about the forcing mechanisms responsible recent work suggests that co2 storage in the deep atlantic ocean played an important role in these events but detailed reconstructions of deep ocean chemical stratification are needed to test this idea and competing hypotheses here we present new records of the nd isotope composition of fish debris and 13c and b ca ratios of benthic foraminifera from the northwest and southeast atlantic ocean our novel geochemical data show that in contrast to major quaternary glaciations such as mis 2 21 ka and mis 100 2 52 ma the deep north atlantic ocean was weakly chemically stratified during mis m2 we show that southern component water incursion into the atlantic ocean was limited to the deep south atlantic basin during mis m2 and peaked well before 10 15 kyr the atmospheric co2 minimum our findings imply that the deep atlantic ocean was not the principle sink of co2 sequestered from the atmosphere during mis m2 implicating a different co2 storage deep water reservoir mechanism presumably southern component water incursion into the pacific ocean weak chemical stratification in the deep atlantic ocean during mis m2 relative to mis 100 and 2 suggests comparatively active atlantic meridional overturning circulation that suggestion is consistent with the warmth of the high latitude north atlantic during mis m2 surface water temperatures cooled during m2 but only close to holocene values our findings may help to explain the paucity of evidence for extensive early glaciation of the northern hemisphere during m2 but leave open the possibility of ice sheet advance on antarctica

late pliocene upwelling in the southern benguela region the late pliocene has been proposed as a possible analogue for understanding future climate change and for testing climate models previous work has shown that during the pliocene the major upwelling systems were relatively warm and that this meant they were either inactive contracted or were upwelling warmer waters than present here we examine evidence from a site located on the margins of the modern benguela upwelling system to test whether the upwelling cells had migrated or contracted relative to present during the pliocene we applied several organic geochemistry proxies and foraminiferal analyses to reconstruct the pliocene history of odp site 1087 31 28 s 15 19 e 1374 m water depth including the uk37 and tex86 indices for reconstructing sea surface temperatures phytoplankton biomarker concentrations and stable isotope ratios for estimating export primary productivity and for oxygen isotope statigraphy and planktonic foraminifera assemblage abundances for inferring water mass changes these proxies show that between 3 5 and 3 0 ma the southern benguela region was cooler than the northern benguela region by 5 c the latter being where the main upwelling cells are found today from the multiproxy data obtained we also infer that more extensive upwelling was present in the southern benguela region during the pliocene than at present and that the benguela upwelling cells shifted northwards after the pliocene epoch as a result of changes in the local wind field we also find evidence that the benguela upwelling was sensitive to the pronounced cooling during the m2 and km2 glacial stages potentially associated with the expansion of sea ice and cooling in antarctica in the late pliocene

climatic evolution of the southern ocean during the pliocene epoch from 4 8 to 2 6 million years ago abstract we studied the paleoclimatic history of the southern ocean during the pliocene before the intensification of northern hemisphere glaciation at 2 4 ma from isotopic and sedimentologic data from odp leg 114 sites subantarctic south atlantic relatively warm climatic conditions prevailed in the southern ocean during the early early pliocene between 4 6 and 4 2 ma as evidenced by benthic and planktonic 18 o values that were generally less than the holocene despite this warmth significant ice rafting episodes are recorded at several drill sites and piston core locations throughout the southern ocean this interval correlates with a eustatic highstand and represents a climatic optimum for the southern ocean when low and mid latitude species migrated into the antarctic and surface waters were warmer than at present although it is generally agreed that this interval was warm in the southern hemisphere divergent opinions exist as to whether this warming led to the partial decay or growth of the antarctic ice sheet a distinct mid pliocene cooling occurred between 3 5 and 3 2 ma as evidenced by an increase in 18 o values of planktonic and benthic foraminifers in hole 704a and by faunal changes indicative of progressive cooling of antarctic surface waters and development of biotic provinciality in the southern ocean during the late pliocene 3 25 2 6 ma planktonic and benthic 18 o values commonly exceeded those of the holocene and several distinct cooling and or ice volume events occurred during the late gauss chron most notably at 2 9 and 2 63 ma faunal studies suggest several northward advances of the polar front zone and expansion of sea ice in the antarctic during this period these events preceded the major climatic transition at 2 4 ma when the pfz moved to the north sea ice expanded in the antarctic and glaciation intensified in both hemispheres

early late pliocene biochronology and surface water temperature variations in the mediterranean a high resolution magnetobiostratigraphy is presented for the early late pliocene in sicily paleomagnetic measurements on samples from 100 stratigraphic levels provide an unprecedented high quality polarity sequence which extends from the upper reversed gilbert to the upper normal gauss subchron the resultant chronology for the early late pliocene provides ages for the following principal mediterranean bioevents 1 fodgloborotalia crassaformis at 3 40 ma 2 prolonged absence ofgloborotalia puncticulata between 3 38 and 3 16 ma 3 loduvigerina rutila at 3 16 ma 4 lodsphaeroidinellopsis seminulina at 3 07 ma 5 lodgloboquadrina altispira at 3 04 ma 6 lodcibicides italicus at 2 96 ma summer and winter surface water temperature estimates for the period 3 50 to 2 92 ma are based on the abundances ofglobigerinoides sacculifer andgloborotalia puncticulata in 111 samples with an average resolution of some 5000 years short term variations in temperature of the surface water and in colour and carbonate content of the sediment are primarily controlled by the equinoxal precession a higher seasonality during deposition of the grey coloured carbonate poor facies suggests that at that time the summer solstice occurred near perihelion whereas an inverse alignment occurred at the time of deposition of white coloured carbonate rich layers this phase relationship between the precession cycle and grey coloured layers is also valid for the sapropels which began to intercalate in the grey coloured layers at 2 94 ma long term changes in surface water temperatures include a warming between 3 38 and 3 18 ma followed by a cooling from 3 18 to 3 03 ma the warming of mediterranean surface waters at 3 38 ma is believed to be associated with the final closure of the isthmus of panama consequent strengthening of the gulf stream injected larger volumes of warm surface water into the north atlantic drift and eastern boundary current and this caused surface water temperatures in the mid to high latitude northeast atlantic and mediterranean to rise the subsequent climatic cooling at 3 18 ma is linked to a first stage of northern hemisphere continental ice growth

tertiary ice sheet dynamics the snow gun hypothesis we observe strong negative correlation between tertiary low to mid latitude planktonic foraminiferal 18o and the difference between these data and coeval benthic foraminiferal 18o late quaternary data do not show this correlation coupling statistical model 18o comparisons and evidence for antarctic ice and ocean temperature variation we infer that tertiary ice volume recorded by tropical planktonic 18o increased as the deep ocean warmed because the isotopic signatures of deepwater temperature variation and ice volume change were of opposite sign the sum of these signals in tertiary benthic 18o became lost in the noise this renders low correlation between tertiary planktonic and benthic 18o time series compared to late quaternary data we contend that tertiary ice sheet growth was commonly driven by warming of deep water from low to mid latitude marginal seas snow gun hypothesis in contrast late quaternary ice sheets grew as deep water formed at high latitude cooled because tectonic forcing and orbital forcing at low latitude primarily controlled production and temperature variations of this warm saline deep water these influences largely dictated tertiary ice volume fluctuations through the tertiary we infer ice volume fluctuations to be an important component of sea level history on timescales between 103 and 107 years

plio quaternary volcanism in ecuador extensive sampling major element chemistry on over 300 samples and k ar radiometric dating have been carried out on the ecuadorian upper tertiary quaternary volcanoes the results show important space time variations of the volcanic activity between late miocene time and the present in late miocene time a continuous volcanic belt located approximately along the present volcanic front vf affected the whole country from the cuenca basin to the south up to colombia to the north major changes occurred at about 5 ma volcanic activity stopped south of the guayaquil fault belt and never resumed to the north the active volcanic axis shifted eastward to the cordillera real cr area with a simultaneous relative decrease in intensity since early quaternary time the volcanic belt widened westward to the western cordillera where the volcanism resumed at about 1 5 1 0 ma giving rise to the very wide active volcanic zone of ecuador the plio quaternary products show significant longitudinal and latitudinal chemical and mineralogical changes volcanics of the vf and interandean depression contain amphibole and define a calc alkaline trend with a k 2 o content lower than that of the cr products which are characterized by a mostly anhydrous phenocryst assemblage in both areas andesites dominate but extreme compositions basaltic andesites and rhyolites are more diffuse in the cr than the vf no significant transverse zoning has been detected in the northern region north of the chota mira transverse tectonic line the observed temporal and spatial variations are interpreted as a result of the subduction of the carnegie ridge anomalous oceanic crust underthrusting of which began approximately 6 ma ago

late neogene paleoceanography and paleoclimatology of the gulf of aden region based on calcareous nannofossils quantitative study of climatically sensitive nannofossils in the sediments of the gulf of aden has provided a climatic and oceanographic scenario for the northwestern indian ocean during the late neogene the surface water temperature was relatively cold during the latest middle miocene to late miocene 10 7 to 6 32 ma with a probable warm interval in the early late miocene 9 82 to 8 49 ma this cooling is attributed to increased upwelling in the northwestern indian ocean the surface water was relatively warm from the latest late miocene to the middle of the late pliocene 6 32 to 2 59 ma the most intense cooling took place during the late pliocene to early pleistocene 2 59 to 1 69 ma intense upwelling during this interval coincides with worldwide climatic deterioration a probable short warm interval 1 69 to 1 59 ma followed this cold interval in the pleistocene the surface water was cold from 1 59 to 1 00 ma and from 0 61 to 0 24 ma and warm from 1 00 to 0 61 ma and after 0 24 ma

late tertiary history of the antarctic ice sheet evidence from the dry valleys data from the dry valleys antarctica suggest that outlet glaciers of a local ice cap carved primary valley systems on both flanks of the transantarctic mountains while coeval alpine glaciers eroded exposed intervalley mountain ranges subsequently a thick ice sheet overrode the transantarctic mountains at least twice flowing northeastward across major pre existing valleys the youngest overriding episode postdated and the older episode antedated middle to early late miocene time we think that an extensive ice sheet covered east and west antarctica during overriding episodes

equatorial pacific sea surface temperatures faunal patterns and carbonate burial during the pliocene abstract a high resolution record of radiolarian faunal abundances from the eastern equatorial pacific is compared to records of carbonate and noncarbonate burial to examine the evolution of eastern tropical pacific climate processes during the pliocene these data provide a means to evaluate the sensitivity of the equatorial pacific to the onset of northern hemisphere glaciation around 2 8 2 5 ma to the closure of the isthmus of panama around 4 4 3 2 ma and to orogeny related weathering changes before 4 0 ma radiolarian faunal assemblages and sea surface temperature sst estimates indicate a gradual cooling from early to late pliocene but no significant changes occur near the onset of northern hemisphere glaciation records of carbonate and noncarbonate mass accumulation show a long term decrease from the miocene pliocene boundary to the upper pliocene greater carbonate burial in the early pliocene relative to the late pliocene parallels a gradual cooling from early to late pliocene and may reflect changes related to isthmus closure or widespread orogeny no significant time domain changes are seen in the eastern equatorial pacific that could be related to the onset of northern hemisphere glaciation evolutive spectral analyses of these equatorial pacific climate parameters indicate that variance in sst and seasonality commonly concentrate at frequencies not linearly related to orbital variations furthermore cross spectral comparisons with a high resolution benthic 18 o record indicate that the surface ocean and carbonate flux share little coherent variance with high latitude climate processes during the pliocene given the high degree of chronostratigraphic control in these records these results suggest that milankovitch band surface ocean processes as well as carbonate burial in the equatorial pacific are decoupled from high latitude climate processes during the pliocene

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

an overview of the post messinian paleoenvironmental history of the western mediterranean a review of the pliocene pleistocene paleoenvironmental history of the western mediterranean is presented based on micropaleontological and geochemical studies of ocean drilling program odp leg 107 material and marine outcrops in southern italy the calcareous plankton biochronology proposed for the mediterranean by rio et al 1990 and 1991a provides the necessary age control for determining the timing of major climatic and oceanographic changes in the region the early pliocene period in the mediterranean was not a time of warm stable climate rather it was marked by relatively high amplitude climatic oscillations in marginal areas these climatic oscillations resulted in the rhythmic deposition of limestone marl couplets which have an average duration of approximately 19 000 years it is proposed that these sedimentary couplets are the result of precessionally induced changes in monsoon intensity which in turn cause variability in coastal divergence and upwelling the 18o and the calcareous plankton foraminifera and coccoliths records for tyrrhenian sea odp site 653 reveal a cooling of surface waters at 3 1 ma coincident with this cooling is an increase in the frequency of diatomite formation in southern italy bianco section the global cooling at 2 4 ma and the associated expansion of northern hemisphere glaciation resulted in a shift to more arid conditions in the mediterranean region this climate change may have altered the mediterranean water balance resulting in the establishment of antiestuarine water exchange with the atlantic at this time the 18o record for site 653 is also marked by a sharp cooling across the pliocene pleistocene boundary in the boundary stratotype section at vrica this cooling is manifested as an increase in the abundance of the planktonic foraminifer neogloboquadrina pachyderma

pliocene paleoceanography circulation and oceanographic changes associated with the 2 4 ma glacial event high resolution 18o records from the equatorial pacific site 503b equatorial atlantic site 665a and north atlantic site 606a based on the benthic foraminifera cibicidoides wuellerstorfi show the 2 4 ma onset of major northern hemispheric glaciation to be a package of three events occurring at 2 39 2 35 and 2 31 ma in which a periodicity of about 40 kyr is evident the amplitude of the signals at the three sites indicates that these events were 1 2 to 2 3 the size of the latest quaternary glaciation and also indicates cooling of northern source bottom water by 2 7 4 1 c relative to southern source water during glaciations carbon isotopes indicate that southern source waters were less oxygenated than in the quaternary and that there was reduced production of northern source water during glacial intervals the dominant presence of southern source water in the eastern basin of the equatorial atlantic regardless of climatic cycles throughout the late pliocene indicates a greater influence of these waters relative to northern source waters in the late pliocene ocean

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

high resolution late pliocene sea surface temperature record from the northeast atlantic ocean abstract application of quantitative micropaleontologic methods of sea surface temperature sst estimation to the planktic foraminiferal faunas at hole 548 in the northeast atlantic between 3 5 and 2 0 ma provide a detailed record of pliocene surface temperature changes during the onset of major northern hemisphere glaciation sst estimates indicate a relatively warm interval of enhanced interglacials warm peaks between 3 2 and 2 8 ma followed by steady cooling with a significant step like change toward colder temperatures occurring about 2 4 ma this record compares well with faunal and sst records from other north atlantic sites

a chronology of pliocene sea level fluctuations the u s middle atlantic coastal plain record abstract the sequence of marine and marginal marine silts and sands of the u s middle atlantic coastal plain preserves a relatively complete record of pliocene sea level highstands a general chronology for the deposition of these units has been developed previously from studies of the microfossil biostratigraphy complemented by a limited number of paleomagnetic and radiometric dates within this broad temporal framework it is currently difficult to assign ages to individual transgressive events with a resolution much better than 0 5 ma the age model proposed here attempts to refine the depositional history of the atlantic coastal plain by correlation with the more continuous deep ocean record the model assigns probable ages to the pliocene transgressions onto the atlantic coastal plain based on evidence for sea level highstands inferred from high resolution deep ocean 18 o records at least five major transgressive regressive events can be correlated with presumed eustatic fluctuations the temporal resolution for the timing of the transgressive events is greatly improved over that of the biostratigraphy alone many aspects of the proposed chronology require verification by more detailed field study but it is offered as a testable working hypothesis

an alternative suggestion for the pliocene onset of major northern hemisphere glaciation based on the geochemical provenance of north atlantic ocean ice rafted debris abstract the onset of abundant ice rafted debris ird deposition in the nordic seas and subpolar north atlantic ocean 2 72 millions of years ago ma is thought to record the pliocene onset of major northern hemisphere glaciation nhg due to a synchronous advance of north american laurentide scandinavian and greenland ice sheets to their marine calving margins during marine isotope stage mis g6 numerous marine and terrestrial records from the nordic seas region indicate that extensive ice sheets on greenland and scandinavia increased ird inputs to these seas from 2 72 ma the timing of ice sheet expansion on north america as tracked by ird deposition in the subpolar north atlantic ocean however is less clear because both europe and north america are potential sources for icebergs in this region moreover cosmogenic dating of terrestrial tills on north america indicate that the laurentide ice sheet did not extend to 39 n until 2 4 0 14 ma at least 180 ka after the onset of major ird deposition at 2 72 ma to address this problem we present the first detailed analysis of the geochemical provenance of individual sand sized ird deposited in the subpolar north atlantic ocean between mis g6 and 100 2 72 2 52 ma ird provenance is assessed using laser ablation lead pb isotope analyses of single ice rafted 150 m feldspar grains to track when an ice rafting setting consistent with major nhg first occurred in the north atlantic ocean during the pliocene intensification of nhg inhg we investigate when the pb isotope composition 206pb 204pb 207pb 204pb 208pb 204pb of feldspars deposited at dsdp site 611 first resembles that determined for ird deposited at this site during mis 100 2 52 ma the oldest glacial for which there exists convincing evidence for widespread glaciation of north america whilst quaternary magnitude ird fluxes exist at site 611 during glacials from 2 72 ma we find that the provenance of this ird is not constant instead we find that the pb isotope composition of ird at our study site is not consistent with major nhg until mis g2 2 64 ma we hypothesise that ird deposition in the north atlantic ocean prior to mis g2 was dominated by iceberg calving from greenland and scandinavia we further suggest that the grounding line of continental ice on northeast america may not have extended onto the continental shelf and calved significant numbers of icebergs to the north atlantic ocean during glacials until 2 64 ma

pliocene palaeotemperature reconstruction for the southern north sea based on ostracoda abstract the development of a large northeastern atlantic shelf ostracod database has confirmed that an intrinsic relationship exists between watermass temperature and the spatial latitudinal distribution of benthonic shelf ostracoda a second pliocene ostracod database using assemblages from four boreholes in the netherlands and a number of localities from the east anglian neogene succession has also been constructed a quantitative method of modern analogues and the squared chord distance dissimilarity coefficient has been employed as a means of calculating the level of similarity between recent and neogene assemblages and therefore to aid in the reconstruction of palaeotemperatures in the southern north sea basin during the pliocene the results in the form of contoured dissimilarity values indicate the presence of at least seven palaeoceanographical climatic phases between ca 5 2 and 1 6 ma bp an early pliocene cooling phase ecozone a in which the fauna is dominated by the cryophilic species palmenella limicola norman elofsonella concinna jones robertsonites tuberculatus sars neomonoceratina tsurugasakensis tabuki and acanthocythereis dunelmensis norman supervenes a period of stable subtropical conditions in the miocene a mid pliocene warming phase ecozone b which has been documented throughout the north atlantic can be recognized in the faunal composition of the sublittoral ostracod assemblages of both the netherlands and east anglia a hiatus between the coralline and waltonian crags is thought to be associated with a deterioration in climatic conditions recent analogues to the netherlands faunas of ecozone c first phase late pliocene cooling ca 2 9 ma bp indicate a decrease of approximately 5 6 c in mean summer surface temperatures a return to elevated temperatures of a mauritanian aspect can be seen in the fauna of the fa2 zone and waltonian crag this amelioration of climate occurred prior to the praetiglian cold phase second phase late pliocene cooling ca 2 4 ma bp which again saw the reintroduction of cryophilic species including baffinicythere howei hazel fimarchinella logani brady crosskey and robertson and hemicythere emarginata sars into the southern north sea during the newbournian and butleyan stages the final phase of the latest pliocene third phase late pliocene cooling is only documented in the ostracod fauna of the norwich crag evidence in the covariance of loxoconchidae and norwegian provincial cryophilic species indicates that the polar front may have been as much as 2000 km further south during the deposition of the chillesford sand member norwich crag fm ca 2 0 1 6 ma bp