regional warming pliocene 3 ma paleoclimate of europe and the mediterranean the paleoclimate of the middle pliocene ca 3 ma was generally warmer than present particularly at middle to high latitudes it has been suggested that this period may represent an analogue for future climate change mechanisms that have been proposed to account for this warming are enhanced thermohaline circulation and or greater concentrations of co 2 in the atmosphere we present new climate model simulations supported by geological data that suggest that in the european and mediterranean region the climate was warmer by 5 c wetter by 400 1000 mm yr and less seasonal than present modeling results suggest that an intensification of the icelandic low pressure system and the azores high pressure system occurred during the middle pliocene as a direct result of higher annual sea surface temperatures and reduced ice cover in the northern hemisphere this change increased the surface pressure gradient over the region and strengthened annual westerly wind velocity by 4 m s 1 associated increases in wind stress by 20 n m 2 over the north atlantic ocean may have enhanced the flow of surface currents such as the gulf stream and north atlantic current which in turn would have sustained the higher sea surface temperatures these changes to the regional climate system would have driven greater atmospheric and oceanic transport of heat from equatorial regions to the north atlantic ocean particularly during winter such conditions are proposed as a likely cause of the warming indicated for europe and the mediterranean ca 3 ma

development of vegetation and continental aridity in northwestern africa during the late pliocene the pollen record of odp site 658 abstract a 200 m long marine pollen record from odp site 658 21 n 19 w reveals cyclic fluctuations in vegetation and continental climate in northwestern africa from 3 7 to 1 7 ma these cycles parallel oxygen isotope stages prior to 3 5 ma the distribution of tropical forests and mangrove swamps reached cape blanc 5 n of the present distribution between 3 5 and 2 6 ma forests occurred at this latitude during irregular intervals and nearly disappeared afterwards likewise a saharan paleoriver flowed continuously until isotope stage 134 3 35 ma when river discharge ceased wind transport of pollen grains prevailed over fluvial transport pollen indicators of trade winds gradually increased between 3 3 and 2 5 ma a strong aridification of the climate of northwestern africa occurred during isotope stage 130 3 26 ma afterwards humid conditions reestablished followed by another aridification around 2 7 ma repetitive latitudinal shifts of vegetation zones ranging from wooded savanna to desert flora dominated for the first time between between 2 6 and 2 4 ma as a response to the glacial stages 104 100 and 98 although climatic conditions recorded in the pliocene were not as dry as those of the middle and late pleistocene latitudinal vegetation shifts near the end of the pliocene resembled those of the interglacial glacial cycles of the brunhes chron

plio pleistocene megacycles record of climate and tectonics abstract paleoclimatic records from the deep sea floor show that in the last 3 m y more than 100 oscillations of mild and cool global climate took place with a larger amplitude than any experienced during the holocene variations of dry and wet climates in the chinese loess plateau and in the loess belt of central europe have similar frequency it has been convincingly proved that the periodicity of the past gross climate changes agrees with that of the earth s orbital perturbations however while the amplitude of the orbital cycles and of the oceanic oxygen isotope variations is relatively uniform several of the cold climate episodes recorded on land appear more severe than the remainder they correspond to chinese loess units l1 l2 l5 l6 and l9 correlating with central european loess of cycles b c f h and j these units correspond to oxygen isotope stages 2 6 12 16 and 22 and to the weichselian saalian and elsterian ice advances in addition chinese loess layers l13 l15 wl1 wl2 wl3 and wl4 appear to represent exceptionally dry and cold episodes apparently correlative with the inter bavelian cooling and with menapian eburonian and praetiglian glacials of the rhine delta based on this observation we propose to distinguish within the last 2 5 m y ten megacycles describe them in the chinese loess sequences and name them in the order of increasing age mc1 mc10 each megacycle starts with an unusually thick loess unit interpreted as a deposit of an exceptionally severe glaciation and terminates with a cluster of well developed soils indicative of warm humid climates interrupted by relatively mild glacials the megacycles of the last 2 5 m y lasted between 200 and 340 millennia each with an average duration of 255 thousand years when correlated with the stratigraphic record of the chinese loess plateau the wurm terrace as well as the saale glacier advances the eem marine transgression the weichsel ice advance and the holocene correspond to a still incomplete megacycle mc1 the riss terrace the elster ice advance holstein transgression and subsequent mild and cool intervals ending with the schoningen interglacial sensu urban 1992 belong to the megacycle mc2 recognition of four megacycles within brunhes resolves the long standing discrepancy between the limited number of classical continental glacial and interglacial units and the frequent climate oscillations recorded in the deep sea sediments and the loess sequences only in the holsteinian and eemian interglacials was the crustal rebound delayed enough to permit oceanic transgressions reaching deep inland there is no apparent astronomic reason for the exceptional intensity and deep southward penetration of continental ice sheets during only some of the cold intervals since the differences are much more pronounced on land than in the ocean and since the major ice advances are closely linked with terraces it seems that the megacycles were preconditioned by tectonic movements intermittent pulses of rapid uplift of mountain ranges could have impacted climate worldwide by deflecting atmospheric circulation in the sense of ruddiman and raymo 1988 it is also probable that the tectonically changing shape of the sea floor sills reoriented the oceanic circulation which then could have affected plio pleistocene climates world wide the loess covered terraces in the lanzhou area demonstrate that the tectonic movements in the northern part of the tibet plateau correlate closely with the advances of continental ice in europe suggesting that the uplift of the tibet plateau significantly contributed to the gradual climate deterioration of the last million years

climate is the past the key to the future the climate of the holocene is not well suited to be the baseline for the climate of the planet it is an interglacial a state typical of only 10 of the past few million years it is a time of relative sea level stability after a rapid 130 m rise from the lowstand during the last glacial maximum physical geologic processes are operating at unusual rates and much of the geochemical system is not in a steady state during most of the phanerozoic there have been no continental ice sheets on the earth and the planet s meridional temperature gradient has been much less than it is presently major factors influencing climate are insolation greenhouse gases paleogeography and vegetation the first two are discussed in this paper changes in the earth s orbital parameters affect the amount of radiation received from the sun at different latitudes over the course of the year during the last climate cycle the waxing and waning of the northern hemisphere continental ice sheets closely followed the changes in summer insolation at the latitude of the northern hemisphere polar circle the overall intensity of insolation in the northern hemisphere is governed by the precession of the earth s axis of rotation and the precession and ellipticity of the earth s orbit at the polar circle a meridional minimum of summer insolation becomes alternately more and less pronounced as the obliquity of the earth s axis of rotation changes feedback processes amplify the insolation signal greenhouse gases h2o co2 ch4 cfcs modulate the insolation driven climate the atmospheric content of co2 during the last glacial maximum was approximately 30 less than during the present interglacial a variety of possible causes for this change have been postulated the present burning of fossil fuels deforestation and cement manufacture since the beginning of the industrial revolution have added co2 to the atmosphere when its content due to glacial interglacial variation was already at a maximum anthropogenic activity has increased the co2 content of the atmosphere to 130 of its previous holocene level probably higher than at any time during the past few million years during the late cretaceous the atmospheric co2 content was probably about four times that of the present the level to which it may rise at the end of the next century the results of a campanian 80 ma climate simulation suggest that the positive feedback between co2 and another important greenhouse gas h2o raised the earth s temperature to a level where latent heat transport became much more significant than it is presently and operated efficiently at all latitudes atmospheric high and low pressure systems were as much the result of variations in the vapor content of the air as of temperature differences in our present state of knowledge future climate change is unpredictable because by adding co2 to the atmosphere we are forcing the climate toward a greenhouse mode when it is accustomed to moving between the glacial interglacial icehouse states that reflect the waxing and waning of ice sheets at the same time we are replacing freely transpiring c3 plants with water conserving c4 plants producing a global vegetation complex that has no past analog the past climates of the earth cannot be used as a direct guide to what may occur in the future to understand what may happen in the future we must learn about the first principles of physics and chemistry related to the earth s system the fundamental mechanisms of the climate system are best explored in simulations of the earth s ancient extreme climates

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

cool la nina during the warmth of the pliocene the role of el nino southern oscillation enso in greenhouse warming and climate change remains controversial during the warmth of the early mid pliocene we find evidence for enhanced thermocline tilt and cold upwelling in the equatorial pacific consistent with the prevalence of a la nina like state rather than the proposed persistent warm el nino like conditions our pliocene paleothermometer supports the idea of a dynamic ocean thermostat in which heating of the tropical pacific leads to a cooling of the east equatorial pacific and a la nina like state analogous to observations of a transient increasing east west sea surface temperature gradient in the 20th century tropical pacific

modeling the middle pliocene climate with a global atmospheric general circulation model 1 a new climate simulation for the middle pliocene ca 3 ma bp is performed by a global grid point atmospheric general circulation model developed at the institute of atmospheric physics iap agcm with boundary conditions provided by the u s geological survey s pliocene research interpretations and synoptic mapping prism group it follows that warmer and slightly wetter conditions dominated at the middle pliocene with a globally annual mean surface temperature increase of 2 60 c and an increase in precipitation of 4 0 relative to today at the middle pliocene globally annual terrestrial warming was 1 86 c with stronger warming toward high latitudes annual precipitation enhanced notably at high latitudes with the augment reaching 33 5 32 5 of the present value at 60 90 n 60 90 s on the contrary drier conditions were registered over most parts at 0 30 n especially in much of east asia and the northern tropical pacific in addition both boreal summer and winter monsoon significantly decreased in east asia at the middle pliocene it is indicated that the iap agcm simulation is generally consistent with the results from other atmospheric models and agrees well with available paleoclimatic reconstructions in east asia additionally it is further revealed that the prism warmer sea surface temperature and reduced sea ice extent are main factors determining the middle pliocene climate the simulated climatic responses arising from the prism reconstructed vegetation and continental ice sheet cannot be neglected on a regional scale at mid to high latitudes like over greenland and the qinghai tibetan plateau and around the circum antarctic but have little influence on global climate

last interglacial and holocene altithermal environments in south africa and namibia micromammalian evidence abstract climatic interpretations are derived indirectly from evidence for vegetation changes based on the remains of micromammals small rodents and shrews from archaeological sites thus far only border cave has provided evidence apparently referable to the earlier altithermal in oxygen isotope substage 5e vegetation zones and by implication climatic zones apparently extended 3 and more south of their present southern limits rainfall may have been up to 100 more than it is today and much more seasonal with drier winters mean annual temperatures were perhaps about 1 c higher on other evidence eight other sites provide evidence concerning conditions during the holocene altithermal 7000 6000 yr b p the evidence seems to indicate relatively low annual precipitation in the main summer rainfall region and an extended rainfall season in the southwestern winter rainfall region it is less clear whether or not annual rainfall was relatively high at this time in the latter region although in the namib desert conditions were apparently wetter this tends to agree with the dry period analogue of cockcroft et al 1987 and would imply reduced seasonality of precipitation throughout the region in contrast to the situation during the earlier altithermal apparent conflict with palynological evidence may be explainable but requires further examination

climate and biomes in the west mediterranean area during the pliocene a new pollen derived method of climatic quantification based on the mutual climatic range of plant taxa has been applied to 17 pliocene pollen sequences in the west mediterranean area the latitudinal gradient observed in the pollen data was confirmed by the climatic reconstructions there is a gradient from north to south both for temperatures and precipitation at the beginning of the pliocene 5 32 5 ma the climate in the north mediterranean area was on average warmer and more humid than today respectively 1 4oc and 400 700 mm in the south mediterranean region the climate was both warmer and drier than today respectively equal to or 5oc higher and drier or equal humidity the pollen based climate estimates were then used to reconstruct biomes for the region the results show the occurrence of three biomes the broad leaved evergreen warm mixed forest the xerophytic woods scrub biome and the warm grass shrub biome these biomes are still represented today in the mediterranean region despite different thermic and water conditions

bioclimatic analysis of rodent palaeofaunas reveals severe climatic changes in southwestern europe during the plio pleistocene abstract a recently developed method in palaeoclimatology bioclimatic analysis which makes it possible to extract a maximum of information from the available mammal proxy data is applied to a succession of fossil rodent assemblages recorded from the pliocene and pleistocene in the iberian peninsula it consists of both qualitative and quantitative models with the capacity to produce a detailed palaeoclimate reconstruction which is consistent with palaeobotanical and isotopic proxy data and the physics of atmospheric models using this method the palaeoclimate of the iberian plio pleistocene is reconstructed with high resolution from 44 fossil rodent assemblages comprising more than a hundred identified species analysis of these assemblages shows that the climatic evolution of the iberian peninsula during the plio pleistocene can be divided into four distinct climatic phases first a long phase of subtropical climate with summer rainfall and winter drought occurred during the ruscinian second between 3 4 and 2 5 my b p there was a cooling phase coincident with the development of the northern hemisphere ice sheets following this cooling a temperate interlude occurred between 2 5 and 1 8 my b p during this phase the mediterranean climate was established permanently in southwestern europe finally during the pleistocene temperate and colder stages were succeeding in relationship with the northern hemisphere glaciations this sequence of climatic changes is linked with the tectonic rising of the central asian and east african plateaus variations in the atmospheric circulation pattern and changes in the mediterranean sea surface temperatures all these factors led to associated changes in the precipitation regime and a latitudinal displacement of the zonal climatic belts

quaternary mammals and the end villafranchian dispersal event a turning point in the history of eurasia the history of land mammals is characterized by dispersal events i e short periods of rapid intercontinental migrations and faunal replacements one of these the elephant equus event of lindsay et al may be dated somewhere between 3 and 2 5 ma a second event the wolf event may fall near 1 7 ma the end villafranchian event is discussed in detail it may be dated between 1 0 and 0 9 ma and is marked by a practically total rejuvenation of the fauna with the appearance of new types of adaptation unknown in the villafranchian this faunal revolution is easily recognized all over eurasia and is accompanied by wide ranging changes in climate and vegetation this whole sequence of phenomena may have been triggered by extensive tectonic movements in the mountain belts of central and southern asia

late cenozoic uplift in southern asia and the american west rationale for general circulation modeling experiments geologic evidence suggests significant increases in uplift rates and absolute elevation in several areas during the late cenozoic especially in the last 10 m y regions of major uplift include the tibetan plateau and himalayan mountains of southern asia and the sierra nevada colorado plateau basin and range rocky mountains and high plains of the american west uplift occurred at a scale large enough to affect regional and global climate in a number of ways several of which we evaluate by general circulation model experiments in accompanying papers

final closure of panama and the onset of northern hemisphere glaciation abstract the greenland ice sheet is accepted as a key factor controlling the quaternary glacial scenario however the origin and mechanisms of major arctic glaciation starting at 3 15 ma and culminating at 2 74 ma are still controversial for this phase of intense cooling ravelo et al 1 a c ravelo d h andreasen m lyle a o lyle m w wara regional climate shifts caused by gradual global cooling in the pliocene epoch nature 429 2004 263 267 proposed a complex gradual forcing mechanism in contrast our new submillennial scale paleoceanographic records from the pliocene north atlantic suggest a far more precise timing and forcing for the initiation of northern hemisphere glaciation nhg since it was linked to a 2 3 c surface water warming during warm stages from 2 95 to 2 82 ma these records support previous models g h haug r tiedemann effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation nature 393 1998 673 676 2 claiming that the final closure of the panama isthmus 3 0 2 5 ma j groeneveld s steph r tiedemann d nurnberg d garbe schonberg the final closure of the central american seaway geology in prep 3 induced an increased poleward salt and heat transport associated strengthening of north atlantic thermohaline circulation and in turn an intensified moisture supply to northern high latitudes resulted in the build up of nhg finally culminating in the great irreversible climate crash at marine isotope stage g6 2 74 ma in summary there was a two step threshold mechanism that marked the onset of nhg with glacial to interglacial cycles quasi persistent until today

simulations of warm tropical conditions with application to middle pliocene atmospheres during the early and mid pliocene the period from 5 to 3 million years ago approximately the earth is believed to have been significantly warmer than it is today but the reasons for the higher temperatures are unclear this paper explores the impact of recent findings that suggest that at that time cold surface waters were absent from the tropical and subtropical oceanic upwelling zones el nino was in effect a perennial rather than intermittent phenomenon and sea surface temperatures in low latitudes were essentially independent of longitude when these conditions are specified as the lower boundary condition for an atmospheric gcm we find that the trade winds along the equator and hence the walker circulation collapse the low level stratus clouds in low latitudes diminish greatly thus reducing the albedo of the earth the atmospheric concentration of water vapor increases and enhanced latent heat release due to stronger evaporation warms up the tropical atmosphere particularly between 40 s and 20 n moreover teleconnection patterns from the pacific induce a warming over north america that is enhanced by surface albedo feedback a process that may have helped to maintain this region ice free before 3 ma the results presented here indicate that the suggested absence of cold surface waters from the tropical and subtropical oceanic upwelling zones could have contributed significantly to the pliocene warmth

astronomic timescale for the pliocene atlantic δ18o and dust flux records of ocean drilling program site 659 high resolution benthic oxygen isotope and dust flux records from ocean drilling program site 659 have been analyzed to extend the astronomically calibrated isotope timescale for the atlantic from 2 85 ma back to 5 ma spectral analysis of the 18o record indicates that the 41 kyr period of earth s orbital obliquity dominates the pliocene record this is shown to be true regardless of fundamental changes in the earth s climate during the pliocene however the cycles of sahelian aridity fluctuations indicate a shift in spectral character near 3 ma from the early pliocene to 3 ma the periodicities were dominantly precessional 19 and 23 kyr and remained strong until 1 5 ma subsequent to 3 ma the variance at the obliquity period 41 kyr increased the timescale tuned to precession suggests that the pliocene was longer than previously estimated by more than 0 5 m y

forcing of late cenozoic northern hemisphere climate by plateau uplift in southern asia and the american west geologic evidence indicates that net vertical uplift occurred on a large kilometer scale and at accelerating rates during the middle and late cenozoic in plateaus of southern asia and the american west based on this evidence general circulation model sensitivity tests were run to isolate the unique effects of plateau uplift on climate the experiments simulated significant climatic changes in many places some far from the uplifted regions the basic direction of most of these simulated responses to progressive uplift is borne out by changes found in the geologic record winter cooling of north america northern europe northern asia and the arctic ocean summer drying of the north american west coast the eurasian interior and the mediterranean winter drying of the north american northern plains and the interior of asia and changes over the north atlantic ocean conducive to increased formation of deep water the modeled changes result from increased orographic diversion of westerly winds from cyclonic and anticyclonic surface flow induced by summer heating and winter cooling of the uplifted plateaus and from the intensification of vertical circulation cells in the atmosphere caused by exchanges of mass between the summer heated and winter cooled plateaus and the mid latitude oceans disagreements between the geologic record and the model simulations in alaska and the southern rockies and plains may be related mainly to the lack of narrow mountain barriers in the model orography taken together the observed regional trends comprise much of the pattern of late cenozoic climatic deterioration in the northern hemisphere that culminated in the plio pleistocene ice ages the success of the uplift sensitivity experiment in simulating the correct pattern and sign of most of the observed regional climatic trends points to uplift as an important forcing function of late cenozoic climatic change in the northern hemisphere at time scales longer than orbital variations however the modest amplitude of the uplift induced cooling simulated at high latitudes indicates a probable need for additional climatic forcing

rodent paleofaunas as indicators of climatic change in europe during the last 125 000 years abstract this paper presents a quantitative reconstruction of the european late pleistocene paleoclimate based on 72 rodent assemblages of five sequences from france germany and bulgaria covering the last interglacial glacial cycle they show a pattern of severe changes in temperature with reduced precipitation during the coldest periods a tentative correlation between the isotopic and palynological records and the paleotemperature changes is shown these changes are consistent with variations in atmospheric circulation patterns in response to an expanding retracting fennoscandian ice sheet they can be attributed to the enhancement weakening of the scandinavian polar anticyclone and its associated dry winds the south north shifting of the north atlantic polar front and the varying supply of moist air from the atlantic qualitative paleoenvironmental analysis shows broadleaved deciduous forests in france and bulgaria during most of the studied period taiga and tundra appeared in eastern france during the lower wurm the german sequence indicates the presence of coniferous forests these results are broadly consistent with other paleobiological records mammalian avian and insect faunas isotopic record in dental tissue palynology the main discrepancies with the paleoclimate inferred from the palynological record are found during the coldest periods and are probably due to the interaction between vegetation climate and atmospheric co2 levels

regional scale palaeoclimate modelling on soft proxy data basis an example from the upper miocene of the lower rhine embayment abstract a new method in palaeoclimatology initially proposed by mosbrugger and schilling 1992 which makes it possible to extract a maximum of information from the available proxy data is tested it possesses a capacity to produce a detailed palaeoclimate reconstruction which is consistent with both proxy data and the physics of atmospheric models since proxy data information is particularly poor on a global scale our method focuses on smaller scale regions of better proxy data coverage it consists of an iterative coupling of inverse mesoscale atmospheric modelling with proxy based palaeoclimate reconstruction using this method the palaeoclimate of the tortonian upper miocene of the lower rhine embayment northwest germany is reconstructed with a high spatial resolution the results include a physically consistent inter and extrapolation of proxy derived palaeoclimate data in space and onto variables not accessible from geological palaeontological proxies alone moreover the method delivers statistics of the large scale atmospheric flows as information on the coupling of the regional climate to global fields

reassessment of the position of the plio pleistocene boundary is there a case for lowering it to the gauss matuyama palaeomagnetic reversal forty eight years have elapsed since formal discussions were initiated in 1948 on the position of the pliopleistocene boundary at the 18th international geological congress held in london during that year the commission on the plio pleistocene boundary recommended that the lower pleistocene should include as its basal member the marine calabrian formation together with its terrestrial continental equivalent the villafranchian king and oakley 1950 p 214 the suitability of the base of the calabrian as the plio pleistocene boundary was specifically linked to the first appearance within the lowermost calabrian as then defined of the cryophilic mollusc species arctica islundica and hyalinea baltica according to the evidence given this usage would place the boundary at the horizon of the first indication of climatic deterioration in the italian neogene succession king and oakley op cit from the time of the adoption of this resolution until the acceptance at the 27th international congress in moscow some 36 years later of the global stratotype section and point gssp at vrica as defining the plio pleistocene boundary considerable advances in the understanding of the marine plio pleistocene succession in southern italy and in defining and placing within a sound chronological framework important global biostratigraphic and climatic events in both marine and terrestrial sequences have opened to question the appropriateness of the 1948 definition the adoption of the vrica gssp in 1984 at a stratigraphic position essentially in keeping with the spirit of the 1948 resolution represents in the view of the writer and a number of other quatemary stratigraphers a compromise between historical usage and recent advances in plio pleistocene stratigraphy which fully satisfies neither tradition nor the evidence of modem stratigraphy it seems somewhat ironical that at a time of rapid advances in marine isotope stratigraphy and both terrestrial and marine chronostratigraphy the stamp of approval was given to a stratotype whose position had been advocated in the light of the stratigraphic knowledge prevailing a full generation earlier there is no question that the formal requirements for the definition of the vrica gssp were met in 1984 and that the boundary as placed presently at 1 8 ma must be accepted as dividing the pliocene from the pleistocene what is however strongly questioned by many including the present writer is whether it is justified to maintain a boundary whose position is rooted in priority and historical usage rather than current evidence for the considerable earlier onset of a climatic regime which gives an essential unity to the pleistocene and is clearly mirrored in the global stratigraphic record lowering of the boundary to this position would not only be in keeping with the 1948 conclusion that it be placed at the fust indication of climatic deterioration in the neogene succession but would facilitate correlation through the marked lithostratigraphic and palaeontological changes with which it is associated in terrestrial sequences through the unique marine isotopic signature with which it coincides and through its correspondence with a major palaeomagnetic reversal the gauss matuyama at 2 6 ma these considerations must necessarily be viewed against the background of the desirability of stability in lithostratigraphic classification and the relative recency of the acceptance of the present gssp intemational stratigraphic correlation should certainly not be viewed as transient and subject to the whims or fashions of the day

diatom constraints on the position of the antarctic polar front in the middle part of the pliocene abstract the relative percentages of diatom taxa in 5 deep sea cores dsdp 266 odp 699a odp 747a odp 751 a and eltanin core 50 28 from the southern ocean are determined for an interval centered on 3 1 to 2 9 ma in the middle part of the pliocene this climatically warm interval which is being studied by the prism project of the u s geological survey coincides with a proposed interval of major deglaciation of east antarctica the maximum southerly position of the antarctic polar front between 3 1 and 3 0 ma is inferred from these diatom studies the presence of calcareous nannofossils in the sediments and sedimentologic and micropaleontologic information from the literature it is suggested that the antarctic polar front may have migrated by as much as 6 of latitude further to the south in the southeastern atlantic and indian oceans during this pliocene warm interval but probably lay close to its present day position in the southwest atlantic and drake passage summer sea surface temperatures are inferred to have been no more than 3 4 c warmer than present at latitudes between 55 and 60 s

speleothem calcite farmed in situ modern calibration of δ18o and δ13c paleoclimate proxies in a continuously monitored natural cave system abstract understanding the relationships between speleothem stable isotopes 13 c 18 o and in situ cave forcing mechanisms is important to interpreting ancient stalagmite paleoclimate records cave studies have demonstrated that the 18 o of inorganically precipitated low temperature speleothem calcite is systematically heavier than the 18 o of laboratory grown calcite for a given temperature to understand this apparent offset rainwater cave drip water groundwater and modern naturally precipitated calcite farmed in situ were grown at multiple locations inside hollow ridge cave in marianna florida high resolution micrometeorological air chemistry time series and ventilation regimes were also monitored continuously at two locations inside the cave supplemented with periodic bi monthly air gas grab sample transects throughout the cave cave air chemistry and isotope monitoring reveal density driven airflow pathways through hollow ridge cave at velocities of up to 1 2 m s 1 in winter and 0 4 m s 1 in summer hollow ridge cave displays a strong ventilation gradient in the front of the cave near the entrances resulting in cave air that is a mixture of soil gas and atmospheric co 2 a clear relationship is found between calcite 13 c and cave air ventilation rates estimated by proxies pco 2 and 222 rn calcite 13 c decreased linearly with distance from the front entrance to the interior of the cave during all seasons with a maximum entrance to interior gradient of 13 c caco3 7 a whole cave hendy test at multiple contemporaneous farming sites reveals that ventilation induces a 1 9 0 96 13 c offset between calcite precipitated in a ventilation flow path and calcite precipitated on the edge or out of flow paths this interpretation of the hendy test has implications for interpreting 13 c records in ancient speleothems calcite 13 c caco3 may be a proxy not only for atmospheric co 2 or overlying vegetation shifts but also for changes in cave ventilation due to dissolution fissures and ceiling collapse creating and plugging ventilation windows farmed calcite 18 o was found to exhibit a 0 82 0 24 offset from values predicted by both theoretical calculations and laboratory grown inorganic calcite unlike 13 c caco3 oxygen isotopes showed no ventilation effects i e 18 o caco3 appears to be a function of growth temperature only although we cannot rule out a small effect of unmeasured gradients in relative humidity evaporation accompanying ventilation our results support the findings of other cave investigators that water calcite fractionation factors observed in speleothem calcite are higher that those measured in laboratory experiments cave and laboratory calcite precipitates may differ mainly in the complex effects of kinetic isotope fractionation combining our data with other recent speleothem studies we find a new empirical relationship for cave specific water calcite oxygen isotope fractionation across a range of temperatures and cave environments 1000 ln 16 1 10 3 t 1 24 6 with a fractionation temperature dependence of 18 o t 0 177 c lower than the currently accepted 0 206 c

les rongeurs de l eocene terminal et de l oligocene d europe comme indicateurs de leur environnement abstract palaeoecological interpretation of the occurrence of certain rodents in late eocene and oligocene strata from western europe is based on the establishment of five dental categories roughly linked with diet and environment time changes in species diversity and relative abundance in these categories are analyzed for the late eocene and oligocene periods the sequence is geographically limited quercy auvergne to avoid the mixing of environments that results from too general compiling cooling at the beginning of the late eocene created open areas testified by the occurrence of hypsodont rodents the great decrease in rodent diversity and species turnover at the grande coupure is probably related to the important decrease in temperature at the eocene oligocene boundary the less important diversity decrease at the mas de pauffie level mp 26 is perhaps an indication of a recurrent cooling at the beginning of the late oligocene maximum aridity also occurred at this level the calibration and correlation of these events with global events like the 29 ma decrease in temperature or the 30 ma great marine regression are discussed the decrease in abundance of issiodoromys with the great increase in species iversity of categories i and ii no to weakly hypsodont teeth during the late oligocene mark the development of forests related to increased moisture and temperature the analysis of time specific changes in the theridomyidae from their first occurrence to their extinction is related to the principal environmental events

plio pleistocene ice volume antarctic climate and the global δ18o record we propose that from 3 to 1 million years ago ice volume changes occurred in both the northern and southern hemispheres each controlled by local summer insolation because earth9s orbital precession is out of phase between hemispheres 23 000 year changes in ice volume in each hemisphere cancel out in globally integrated proxies such as ocean 18 o or sea level leaving the in phase obliquity 41 000 years component of insolation to dominate those records only a modest ice mass change in antarctica is required to effectively cancel out a much larger northern ice volume signal at the mid pleistocene transition we propose that marine based ice sheet margins replaced terrestrial ice margins around the perimeter of east antarctica resulting in a shift to in phase behavior of northern and southern ice sheets as well as the strengthening of 23 000 year cyclicity in the marine 18 o record

pluvial climatic episodes in north america and north africa types and correlation with global climate abstract differences in late quaternary pluvial chronologies among the world s deserts can be related to fundamental differences in the climatology of those pluvial episodes paleoenvironmental records and climate model simulations for two northern hemisphere desert regions are used to illustrate two types of pluvial climatic regime in the higher latitude deserts of the american southwest pluvial conditions during the last glacial maximum were caused by the southward displacement of the westerly jet stream in turn caused by the blocking effect of laurentide ice sheet and a steepened arctic equator pressure gradient winter seasonality of precipitation and substantially lower mean annual temperatures are reflected in the paleoenvironmental record and simulated by models of 18 000 yr b p climate a second pluvial climate type which strongly influences the lower latitude deserts of north africa is characterized by enhanced summer monsoons and occurs during interglacials and perhaps interstadials the primary forcing mechanism of the last pluvial episode in the sahara and libyan deserts appears to have been increased solar radiation milankovitch forcing causing thermally enhanced ocean land pressure gradients and increased flow of maritime tropical air into the interior of the continent poleward displacement of the summer monsoon is consistent with floristic evidence for summer seasonality of precipitation and replicated by model simulations of 9000 and 6000 yr b p climate chronologies from some deserts such as the southern portion of the american southwest suggest the consecutive occurrence of both types of pluvial climatic regime pluvial conditions during the last glacial maximum were brought about by the equatorward displacement of the prevailing westerlies a subsequent more subdued pluvial period occurred later between 12 500 and 8000 yr b p caused by the poleward displacement of summer monsoons characterization of the climatology of pluvial episodes generates explanations for their temporal distribution and therefore this approach may be useful in assessing the quaternary chronology of pluvial episodes in other desert regions

duration and structure of the past four interglaciations reanalysis and additional dating of the devils hole 18o paleotemperature record confirm that the last interglaciation in the great basin the continental analog of marine isotopic substage 5e lasted 22 000 yr consistent with the vostok paleotemperature record which suggests a duration of 19 000 yr for this event in antarctica the three preceding interglaciations in the devils hole record analogs of marine isotopic substages 7e 9c and 11c range from 20 000 to 26 000 yr in duration a 20 000 yr duration for the last interglaciation is consistent with tims uranium series dated sea level high stands thus the widely held view that interglaciations were of 11 000 to 13 000 yr duration and constituted only about 10 of mid to late pleistocene climatic cycles needs reexamination the warmest portion of each interglaciation in the devils hole time series is marked by a 18o plateau signifying apparent climatic stability for periods of 10 000 to 15 000 yr duration

oxygen isotope fractionation between calcite and tremolite an experimental study oxygen isotope partitioning between calcite and tremolite was experimentally calibrated in the presence of small amounts of a supercritical co2 h2o fluid at temperatures from 520 to 680 c and pressures from 3 to 10 kbar the experiments were carried out within the stability field of the calcite tremolite assemblage based on phase equilibrium relationships in the system cao mgo sio2 co2 h2o so that decomposition of calcite and tremolite was avoided under the experimental conditions appropriate proportions of carbon dioxide to water were used to meet this requirement large weight ratios of mineral to fluid were employed in order to make the isotopic exchange between calcite and tremolite in the presence of a fluid close to that without fluid the data processing method for isotopic exchange in a three phase system has been applied to extrapolate partial equilibrium data to equilibrium values the determined fractionation factors between calcite cc and tremolite tr are expressed as 1031n cc tr 3 80 106 t2 1 67

geographic and temporal patterns in the late neogene 12 3 ma aridification of europe the use of small mammals as paleoprecipitation proxies abstract present day relations between small mammal community structure and rainfall are used to predict late neogene 12 3 ma precipitation patterns in europe and anatolia new proxy methods are developed which include regressions of mean annual and minimum monthly precipitation on diet invertivory index and locomotion habitat arboreality index a series of precipitation maps and a set of regional precipitation curves through time at 1 myr resolution are presented precipitation curves at a higher temporal resolution are constructed for the region of central spain the miocene results show the existence between 12 and 9 ma of a large wet 800 1200 mm yr zone extending from northern spain to the ukraine and characterized by the whole year penetration of large amounts of moisture far into the continent between 10 9 and 5 ma this european temperate wet zone etwz shrinks and or moves northward resulting in diachronous aridification a coeval northward migration of the subtropical high pressure zone shpz is hypothesized which is also consistent with the predicted onset of seasonal summer dryness between 10 and 8 ma the maximum extension of the etwz at 12 9 ma temporally correlates with northern hemisphere cooling suggesting that climate zonation rather than the global amount of atmospheric moisture controlled european climate at this time the main aridification at 9 8 ma could best be explained by a northward extension shifting of the subtropical high pressure zone and a transition towards less zonal circulation processes which ultimately could have been triggered by uplift of the tibetan plateau a temporary increase of precipitation at 7 6 ma is associated with renewed global cooling the lowest precipitation values less than 400 mm yr occur during the pliocene in southern and eastern europe uplift in eastern europe carpathians shrinking of the paratethys could well explain the aridification in this area and the associated sharpening of east west precipitation gradients across the continent

reconstruction of the late miocene climate of spain using rodent palaeocommunity successions an application of end member modelling abstract end member modelling is applied to a data set of relative abundances of 67 upper miocene rodent associations 11 6 ma from spain france austria and greece the analysis results in the robust estimation of relative levels of four climatic parameters humidity temperature seasonality type and predictability in the preparatory stage species are aggregated into nine groups on the basis of ecological criteria humidity preferences and adaptations are based on actualistic and functional morphological interpretations of dentition and locomotion temperature preferences are inferred from palaeobiogeographic distributions levels of adaptation to seasonality type wet dry or cool warm seasonality are assigned on the basis of diversities in present day climate vegetation zones and the ability of extant relatives to hibernate demographic data are used to formulate adaptations to climatic un predictability in the modelling stage the compositions are unmixed into the contributions of four end members these four extreme theoretical rodent compositions are interpreted in climatic terms and their contributions to the samples are used for the estimation of climatic parameters the subset of 44 well dated rodent compositions from the calatayud daroca and teruel basins ne spain is used to construct detailed climatic curves for the late miocene while the geographical dimension in the data set is used to calculate inter basinal differences the model results for spain indicate more humid and cooler conditions between 10 5 and 8 5 ma around 7 and around 6 ma and more arid and warmer conditions before 10 5 between 8 6 and 7 5 ma and around 6 5 ma superimposed on this pattern is a shift from a more predictable cool warm seasonal climate towards a more unpredictable wet dry seasonal climate between 9 4 and 8 2 ma inter basinal comparisons per time slice show that the climate in southern europe was dryer warmer more wet dry seasonal and more unpredictable than in central europe and that the climatic and vegetational boundaries between the two regions were sharp the occurrences of more humid and cooler episodes in spain during the late miocene might be explained by southward migrations of the boundary between a temperate and subtropical dry climatic belt and their associated vegetation types various positive correlations are observed between the rodent based climatic curves for spain and other palaeoclimatic records from the mediterranean and ne atlantic region clay minerals marine fauna stable isotopes the two cooling maxima at 9 4 and 7 ma closely correspond to clusters of marine events which are generally considered to reflect maxima of global ice volume

middle pliocene vegetation reconstructions paleoclimatic inferences and boundary conditions for climate modeling abstract the general characteristics of global vegetation during the middle pliocene warm period can be reconstructed from fossil pollen and plant megafossil data the largest differences between pliocene vegetation and that of today occurred at high latitudes in both hemispheres where warming was pronounced relative to today in the northern hemisphere coniferous forests lived in the modern tundra and polar desert regions whereas in the southern hemisphere southern beech apparently grew in coastal areas of antarctica pliocene middle latitude vegetation differed less although moister than modern conditions supported forest and woodland growth in some regions now covered by steppe or grassland pliocene tropical vegetation reflects essentially modem conditions in some regions and slightly cooler than or warmer than modern climates in other areas changes in topography induced by tectonics may be responsible for many of the climatic changes since the pliocene in both middle and lower latitudes however the overall latitudinal progression of climatic conditions on land parallels that seen in the reconstruction of middle pliocene sea surface temperatures pliocene paleovegetational data was employed to construct a 2 2 global grid of estimated mid pliocene vegetational cover for use as boundary conditions for numerical general circulation model simulations of middle pliocene climates continental outlines and topography were first modified to represent the pliocene landscape on the 2 2 grid a modern 1 1 vegetation grid was simplified and mapped on this pliocene grid and then modified following general geographic trends evident in the pliocene paleovegetation data set

the gran dolina site lower to middle pleistocene atapuerca burgos spain new palaeoenvironmental data based on the distribution of small mammals new palaeoenvironmental data are reported after analysing the distribution of micromammals orders rodentia insectivora chiroptera and lagomorpha in the 11 stratigraphical levels at the gran dolina site td1 td11 early to middle pleistocene atapuerca spain a continental dry and cold climate is inferred at the beginning of the succession td3 to lower td5 the fauna in the upper td5 and in td6 reflects a complex interglacial period with fluctuations in the degree of relative humidity in the lower part of td8 the presence of microtus aff ratticepoides indicates a relatively cold period finally data from upper levels td8b td10 td11 reflect another interglacial period with slight oscillations in relative moisture the different levels at gran dolina are also correlated with oxygen isotope stages ois td3 td4 and td5 may be correlated with ois 22 td6 is correlated with ois 21 lower td8 td8a is correlated with ois 18 upper td8 td8b is correlated with ois 13 or 15 td10 and td11 are correlated with ois 9 or 11

the pliocene paradox mechanisms for a permanent el nino during the early pliocene 5 to 3 million years ago globally averaged temperatures were substantially higher than they are today even though the external factors that determine climate were essentially the same in the tropics el nino was continual or permanent rather than intermittent the appearance of northern continental glaciers and of cold surface waters in oceanic upwelling zones in low latitudes both coastal and equatorial signaled the termination of those warm climate conditions and the end of permanent el nino this led to the amplification of obliquity but not precession cycles in equatorial sea surface temperatures and in global ice volume with the former leading the latter by several thousand years a possible explanation is that the gradual shoaling of the oceanic thermocline reached a threshold around 3 million years ago when the winds started bringing cold waters to the surface in low latitudes this introduced feedbacks involving ocean atmosphere interactions that along with ice albedo feedbacks amplified obliquity cycles a future melting of glaciers changes in the hydrological cycle and a deepening of the thermocline could restore the warm conditions of the early pliocene

aridity and humidity two aspects of the late miocene climate of north africa and the mediterranean abstract the physiography of north africa is not greatly changed from that of the messinian with the drawdown of the mediterranean in the late messinian the then existing river systems were incised into the landscape and emptied into lake cyrenaica which occupied the substantially drained eastern mediterranean basin the record of incision provides a record of the magnitude of the messinian river systems an analysis of these river systems demonstrates that messinian rainfall a consequence of the zeit wet phase was greatest in east and south central north africa in keeping with the derivation of the water mainly from the indian ocean in central north africa the eosahabi river flowed from messinian lake chad eroding the east tibesti valley and cutting a channel which is especially well preserved near the coast of the gulf of sirt the penetrated sediments of lake cyrenaica and the marginal basins of the messinian transgression are known as the upper evaporites and are generally fine clastics gypsarenites and gypsum anhydrite they were rapidly deposited underlying them is the halite of the lower evaporites this sequence of upper and lower evaporites is much like the lower halite of the tortonian south gharib formation and the overlying clastics and anhydrite of the messinian zeit formation in the gulf of suez red sea area this type of sequence is termed an evaporitic couplet and as has been demonstrated for the gulf of suez red sea is a consequence of a transition from a dry to a more humid climate in a restricted or semirestricted basin this transition occurred at about 7 5 ma in the gulf of suez red sea and at about 5 8 ma in the mediterranean the zeit wet phase manifest in the above events developed in association with the initiation and development of the asian monsoon and the drying of the mediterranean it can be understood in terms of the development of an evolving monsoon desert system the asian monsoon was initiated 8 7 ma in association with the uplift of tibet at this time the north african desert zone was displaced northwards to be over the mediterranean and central and eastern north africa became seasonally humid a concept is advanced in which the early stage of the development of the asian monsoon is seen as having two phases alternating at the precessional ca 21 ka cycle one phase transferred moisture from the indian ocean mainly to southern asia the other phase transferred moisture mainly to north africa with the drawdown of the mediterranean at about 5 8 ma the zeit wet phase intensified a further northward movement of the humid and desert zones occurred at the time of drawdown with the messinian and early pliocene transgressions the wet phase ameliorated but a substantial river system still crossed central north africa at about 4 6 ma north africa became drier probably in response to the developing dominance of the features of the monsoon that transferred moisture mainly to southern asia features of the monsoon that are well recognised today

geochemical evidence supporting t c chamberlin s theory of glaciation in 1899 t c chamberlin proposed that the co sub 2 content of the atomsphere decreased during times of enhanced continental erosion ultimately resulting in glacial epochs he ascribed the increase in the rate of chemical weathering relative to the rate of supply of co sub 2 from earth s interior to increased orogenic activity and globally higher average elevations which promoted rapid chemical erosion of silicates the oceanic record of strontium isotopes preserved in marine sediment supports his suggestion that glacial climates during the phanerozoic are in part linked to increases in the rate of global chemical erosion relative to outgassing from earth s interior further the close correspondence of the major tectonic episodes of the late cenozoic to times of increased continental erosion and glaciation suggests that chamberlin s hypothesis of the cause of glacial periods should be revived

vegetation cover in a warmer world simulated using a dynamic global vegetation model for the mid pliocene in this study we employ the triffid top down representation of interactive flora and foliage including dynamics dynamic global vegetation model dgvm and the hadley centre atmospheric general circulation model version 3 hadam3 gcm to investigate vegetation distributions and climate vegetation feedbacks during the mid pliocene and examine the implications of these results for the origins of hominid bipedalism the triffid model outputs support extant palaeoenvironmental reconstructions for the mid pliocene provided by the prism group pliocene research interpretations and synoptic mapping compared to the pre industrial triffid simulates a significant increase in forest cover during the mid pliocene composed of needle leaf trees in the higher latitudes of the northern hemisphere and broad leaf trees in other regions needle leaf trees extend from the arctic coast into the northern mid latitudes the fractional coverage of bare soil declines in north africa the arabian peninsula australia and southern south america a pattern that is consistent with prism s assertion of less extensive arid deserts a significant increase in the fractional coverage of both broad leaf trees in africa and south america in the mid pliocene scenario is not indicative of a major expansion of tropical rainforests rather it represents an expansion of general woodland type habitats the principal impact of using a dgvm on the gcm predicted climatology for the mid pliocene is to reduce minimum and maximum temperature extremes thus reducing the seasonality of temperature over wide regions the predicted pliocene expansion in broad leaf trees in africa is difficult to reconcile with the savannah hypothesis for the evolution of hominid bipedalism rather the results lend credence to an alternative hypothesis which suggests that bipedalism evolved in wooded to forested ecosystems and was for several million years linked to arborealism

iberian plio pleistocene biochronology micromammalian evidence for mns and elmas calibration in southwestern europe a multivariate biochronological analysis of the plio pleistocene iberian rodent fossil record is presented among more than 300 fossil sites 49 sites have been selected the ordination of the fossil sites selected from the iberian peninsula has been achieved by the appearance event ordination method after calibration of this ordination with geochronological dates at some of the localities numerical dates are proposed for all the localities studied hence mammal fossil sites non datable by other means palaeomagnetism radiometric dating etc have been dated with a relatively high degree of confidence final results allow dating of boundaries between the plio pleistocene european land mammal ages elmas or the mammal neogene mn units these boundaries agree with previous studies using magnetostratigraphical calibration of these scales copyright 2004 john wiley sons ltd

the closing of a seaway ocean water masses and global climate change the late neogene witnessed various major paleoceanographic changes that culminated in intense northern hemisphere glaciation nhg the cause and effects of these changes are still debated we use a multiproxy approach to determine the relative timing of the closure of the panama gateway changes in atlantic circulation global cooling and ice sheet growth benthic foraminiferal mg ca records from a pacific and an atlantic site have been produced and are interpreted in terms of bottom water temperatures these mg temperature records are combined with published benthic 13c 18o and erosion records to reconstruct the flow of proto north atlantic deep water proto nadw over the past 12 ma the results suggest that between 12 5 and 10 5 ma and again between about 8 5 and 6 ma a nutrient depleted water mass that was colder by 1 2 c and fresher than the intervening deep water mass filled the atlantic basin this proto nadw became warmer by 1 c and saltier between 6 and 5 ma coincident with the restriction of surface water flow through the central american seaway the mg temperature records define a subsequent global cooling trend of 3 5 c between 5 ma and today early nhg in the late miocene was perhaps related to the formation of the relatively cold fresh proto nadw the formation of the warmer and saltier proto nadw in the early pliocene may have initially limited northern hemisphere ice growth however the increased moisture released at high northern latitudes associated with formation of warm proto nadw coupled with the global temperature decrease of deep and hence polar surface waters likely helped initiate the intense nhg of the plio pleistocene

oxygen isotopic composition of fossil equid tooth and bone phosphate an archive of difficult interpretation abstract variation in the concentration of the stable isotopes of hydrogen oxygen and carbon have been tested in continental records as tools for quantitative or semi quantitative paleoclimatological studies among the different methods the potential use of oxygen isotopes in mammal bone and tooth phosphate has recently been recognized measurements carried out on fossil mammal bones of holocene age and their paleoclimatological interpretation corresponded well with paleontological and paleobotanical records in the case of considerably older fossils diagenetic processes may change the primary oxygen isotopic composition of phosphate fossil horse bones and teeth principally of the species equus stenonis were studied to ascertain how far back in time fossil mammal remains may be considered reliable material for paleoclimatological studies the samples come from 13 different locations in southeastern spain their age ranging from maspinian late pleistocene to middle villafranchian pliocene apart from the variations of the 18o po43 values which may be related to climatic changes it is apparent that the isotopic composition of bones and teeth from the same deposit are frequently rather different from one another the isotopic differences range from a few tenths of one to several this suggests a strong influence of taphonomy over the measured isotopic values of fossils in each deposit time can be considered neither the only variable nor the most important one responsible for the change of the primary isotopic composition of fossils under these conditions it is rather difficult to establish lower or upper limits for the age of fossils to be studied for reliable paleoclimatological information since the limits are directly related to taphonomic history this in turn is related to local environmental conditions and not only to the age of fossils

taxonomic diversity and stratigraphic distribution of mediterranean pliocene bivalves abstract the mollusc disappearance extinction events throughout the mediterranean pliocene suggest the definition of four faunistic units mediterranean pliocene molluscan units mpmus the bivalve taxonomic diversity the paleobiogeographic significance and the chronological classification of each unit are analyzed in detail the boundaries of the mpmus approximate the major climatic changes of the northern hemisphere respectively at 3 0 2 5 and 2 1 ma on the whole the molluscan fauna changes 356 species of shallow water bivalves have been considered record the transition from a tropical unit mpmu1 to a biogeographic unit mpmu4 comparable with that of the recent mediterranean

physiological significance of low atmospheric co2 for plant climate interactions abstract methods of palaeoclimate reconstruction from pollen are built upon the assumption that plant climate interactions remain the same through time or that these interactions are independent of changes in atmospheric co 2 the latter may be problematic because air trapped in polar ice caps indicates that atmospheric co 2 has fluctuated significantly over at least the past 400 000 yr and likely the last 1 6 million yr three other points indicate potential biases for vegetation based climate proxies first c 3 plant physiological research shows that the processes that determine growth optima in plants photosynthesis mitochondrial respiration photorespiration are all highly co 2 dependent and thus were likely affected by the lower co 2 levels of the last glacial maximum second the ratio of carbon assimilation per unit transpiration called water use efficiency is sensitive to changes in atmospheric co 2 through effects on stomatal conductance and may have altered c 3 plant responses to drought third leaf gas exchange experiments indicate that the response of plants to carbon depleting environmental stresses are strengthened under low co 2 relative to today this paper reviews the scope of research addressing the consequences of low atmospheric co 2 for plant and ecosystem processes and highlights why consideration of the physiological effects of low atmospheric co 2 on plant function is recommended for any future refinements to pollen based palaeoclimatic reconstructions

evolution of early middle miocene rodent faunas in relation to long term palaeoenvironmental changes abstract cluster and principal components analyses have been applied to the composite sequence of 59 rodent assemblages from ramblian to lower vallesian deposits in the daroca calamocha area in the calatayud teruel basin north central spain the studied record is thought to represent the interval from the late aquitanian to the end of the serravallian i e early to middle miocene from ca 22 10 5 ma ago the quantitative results are interpreted by using individual rodent taxa as environmental indicators and by extrapolating the predominant adaptive strategies of recent taxonomic groups which also seem to form natural groups on a demographic scheme french et al 1975 a general warming trend starts in the rambian early miocene and continues into the middle aragonisn early middle miocene the cooling in the middle to late aragonian boundary interval is correlated to the middle miocene cooling phase another cooling occurred around the aragonian vallesian boundary late middle miocene we relate a major increase of aridity in the beginning of the middle aragonian ca 16 5 ma to the spread of low biomass vegetation due to intensification of the subtropical belt wolfe 1985 a notable feature around the early middle aragonian boundary indicating a major shift of climatic belts is the reversal of the relationship between our relative temperature and humidity curves before the reversal we find a positive correlation after it a negative correlation around the middle to late aragonian boundary humidity increased again and a further increase of humidity is indicated by the earliest vallesian faunas our data suggest that the nature of favoured adaptive strategy amongst rodents is related in the end to the degree of climatic humidity

towards a middle pleistocene terrestrial climate reconstruction based on herpetofaunal assemblages from the iberian peninsula state of the art and perspectives abstract the pattern of the varying climatic conditions in southern europe over the last million years is well known from isotope studies on deep ocean sediment cores and the long pollen records that have been produced for lacustrine and marine sedimentary sequences from greece italy and the iberian margin however although relative glacial and interglacial intensities are well studied there are still few proxies that permit quantitative terrestrial temperature and precipitation reconstruction in this context fauna based climate reconstructions based on evidence preserved in archaeological or palaeontological sites are of great interest even if they only document short windows of that climate variability because a they provide a range of temperature and precipitation estimates that are understandable in comparison with present climate b they may allow the testing of predicted temperature changes under scenarios of future climate change and c quantitative temperature and precipitation estimates for past glacials and interglacials for specific regions latitudes can help to understand their effects on flora fauna and hominids as they are directly associated with those cultural and or biological events moreover such reconstructions can bring further arguments to the discussion about important climatic events like the mid bruhnes event a climatic transition between moderate warmths and greater warmths during interglacials in this paper we review a decade of amphibian and reptile based climate reconstructions carried out for the iberian peninsula using the mutual ecogeographic range method in order to present a regional synthesis from mis 22 to mis 6 discuss the climate pattern in relation to the mid bruhnes event and the thermal amplitude suggested by these estimates and finally to identify the chronological gaps that have still to be investigated

the environment of early modern humans at border cave south africa micromammalian evidence abstract an enlarged sample of micromammalian remains from border cave has permitted re evaluation of vegetational and climatic conditions at the site from its earlier occupation apparently about 130 kyr b p the indication is that vegetation in the region was initially woodland analogous to miombo brachystegia woodland which today occurs a minimum of 3 latitude north of the site rainfall would have been 25 100 higher than it is today and more seasonal with drier winters mean annual temperature may have been similar to or slightly higher than it is today thereafter perhaps in 18o stage 5b onwards from around 96 kyr b p vegetation and consequently rainfall appear to have become much as they are today namely bush savanna with forest patches supported by rainfall around 800 mm temperatures on the other hand may have been rather lower than they are today and it is possible that 18o stage 4 is represented during this period subsequently during 18o stage 3 the vegetation appears to have been open acacia nigrescens sclerocarya savanna perhaps preceded by mopane colophospermum mopane such vegetation types today being found at lower altitudes in neighbouring swaziland and into the northeastern transvaal rainfall may have been 25 55 lower than it is today and relatively unpredictable while temperatures were marginally lower these conditions persisted until about 24 kyr b p when the cave was apparently abandoned

late pliocene to early mid pleistocene mammals in eurasia faunal succession and dispersal events abstract four major dispersal events mark european villafranchian and galerian faunas about 3 2 0 4 ma the beginning of the villafranchian is evidenced by the arrival of leptobos and of large cervids and felids the fauna still retains typical forest elements mammut tapirus etc the elephant equus event about 2 5 2 6 ma brought in grassland elements elephant horse while several forest dwellers disappeared the massive arrival of a primitive wolf a large hyaena and leptobos etruscus approximately marks the plio pleistocene boundary wolf event about 1 7 ma this was followed by a new wave of prairie fauna praeovibos leptobos vallisarni allophaiomys canis arnensis a coyote canis falconeri possibly a lycaonid cervalces and hippopotamus also arrived at this time the villafranchian galerian transition saw a total faunal turnover with massive extinctions and new previously unknown adaptations end villafranchian event 1 0 0 9 ma the late pleistocene and living fauna of eurasia took its origin at this time mammalian stratigraphy of asia is more poorly known but faunas are easily correlated with european ones and the end villafranchian event is clearly recognised faunal events are correlated with climatic and physiographic changes late himalayan orogeny

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

effect of orogeny plate motion and land sea distribution on eurasian climate change over the past 30 million years the eurasian climates of today 10 million and 3o million years ago are simulated using an atmospheric general circulation model that incorporates realistic continental geography and epicontinental sea distributions the resulting climates compare well with various palaeoclimate records the retreat of the paratethys an epicontinental sea shifts the central asian climate from temperate to continental conditions and plays as important a role as uplift of the himalayan tibetan plateau in driving the asian monsoon changes

mammalian faunas as indicators of environmental and climatic changes in spain during the pliocene quaternary transition abstract the study of mammal communities provides useful knowledge of paleoenvironments and paleoclimates during the quaternary period and better documentation about the main fossil sites is making this task easier paleoecological reconstructions of this study are based on i rodent evolution and species richness ii the cenogram method and iii methods for quantifying climatic parameters these analyses applied to a pliocene quaternary faunal sequence of spain indicate that a climatic change occurred at the end of the pliocene when considerable cooling led to the onset of the glacial interglacial cycles subsequently during the quaternary period alternating environmental patterns occurred with a rather open and arid environment during the cold phases that contrasts with a somewhat more closed and comparatively wet environment during warmer phases these observations are generalized from spain to the remainder of the continent noting that climatic conditions were less harsh and more arid in spain than elsewhere in europe

rodents and climate 1 a model for estimating past temperatures using arvicolids mammalia rodentia abstract analysis of 253 extant mammalian local faunas shows that the number of arvicoline species in each fauna is related to temperature parameters the very high correlation allows us to propose a method to estimate the temperature for fossil faunas bearing arvicoline species from temperate areas to illustrate this method mean annual temperatures were estimated for late pleistocene hungarian localities and for a sequence from the baume de gigny jura france these were compared with results obtained by other techniques multivariate analysis of rodent associations and synthetic analysis of pollen faunal and sedimentological data