impact of global sst gradients on the mediterranean runoff changes across the plio pleistocene transition this work explores the impact of the development of global meridional and zonal sea surface temperature sst gradients on the mediterranean runoff variability during the plio pleistocene transition about 3 ma results show that total annual mean pliocene mediterranean runoff is about 40 larger than during the preindustrial period due to more increased extratropical specific humidity as a consequence of a weakened and extended hadley cell the pliocene northwest africa hydrological network produces a discharge 30 times larger than today our results support the conclusion that during the pliocene the mediterranean water deficit was reduced relative to today due to a larger river discharge by means of a stand alone atmospheric general circulation model we simulate the separate impact of extratropical and equatorial sst cooling on the mediterranean runoff while cooling the equatorial sst does not imply significant changes to the pliocene mediterranean hydrological budget the extratropical sst cooling increases the water deficit due to a decrease in precipitation and runoff consequently river discharge from this area reduces to preindustrial levels the main teleconnections acting upon the mediterranean area today i e the north atlantic oscillation during winter and the monsoon desert mechanism during summer already have a large influence on the climate of our pliocene simulations finally our results also suggest that in a climate state significantly warmer than today changes of the hadley circulation could potentially lead to increased water resources in northwest africa

sea surface temperatures in the eastern equatorial pacific and surface temperatures in the eastern cordillera of colombia during el nino implications for pliocene conditions pliocene el nino like state in colombia

impact processes permafrost dynamics and climate and environmental variability in the terrestrial arctic as inferred from the unique 3 6 myr record of lake el gygytgyn far east russia a review lake el gygytgyn in far east russia is a 3 6 myr old impact crater lake located in an area that has never been affected by cenozoic glaciations nor desiccation the unique sediment record of the l

carbonate periplatform sedimentation by density flows a mechanism for rapid off bank and vertical transport of shallow water fines existing theories of off bank sediment transport cannot account for rapid rates of sedimentation observed in bahama bank and florida shelf periplatform environments analysis of the physical processes operating during winter cold fronts suggests that accelerated off bank transport of shallow water mud may be achieved by sinking off bank flows of sediment charged hyperpycnal super dense platform waters

inter hemispheric asymmetry in the early pleistocene pacific warm pool the position of the southern boundary of the pacific warm pool is shown to have been stable since the early pleistocene based upon a planktic foraminiferal mg ca derived reconstruction of subtropical sea surface temperature in the coral sea this contrasts with previous reconstructions showing warm pool contraction from the north and east and means that the early pleistocene warm pool was more hemispherically asymmetric than its present configuration the latter was not established until 1ma supporting a strengthening of the northern hadley cell which was not replicated in its southern counterpart prior to the mid pleistocene transition copyright 2010 by the american geophysical union

a 4 ma record of thermal evolution in the tropical western pacific and its implications on climate change article i nfo orbital resolution thermal histories over the last 4 ma at odp site 1143 in the tropical western pacific are reconstructed using alkenone paleothermometry the temperature profile is characterized by a steady state of 29 c with fluctuations b1 c before 2 7 ma and by a strong oscillating state from 2 7 ma largely due to cooling by up to 4 c from 29 c in interglacial to 26 c in glacial intervals this implies a relative warm and stable surface hydrography during the early and mid pliocene in this region influenced by the warm pool before temperature decreases in responding to global cooling and the formation of the distinct glacial stages since the late pliocene therefore the smaller sst gradient between tropical eastern and western pacific and between southern and northern south china sea before the late pliocene indicates a super sized pliocene pacific warm pool while the larger sst gradient since then marks progressively intensification of the zonal walker circulation and meridional hadley circulation representing the monsoon circulations in the region the intensification of the walker and hadley circulations over the tropical pacific may also have helped on the onset of glaciations and subsequent deglaciations during the late pliocene and pleistocene 2011 published by elsevier b v

greatly expanded tropical warm pool and weakened hadley circulation in the early pliocene the pliocene warm interval has been difficult to explain we reconstructed the latitudinal distribution of sea surface temperature around 4 million years ago during the early pliocene our reconstruction shows that the meridional temperature gradient between the equator and subtropics was greatly reduced implying a vast poleward expansion of the ocean tropical warm pool corroborating evidence indicates that the pacific temperature contrast between the equator and 32 n has evolved from 2 c 4 million years ago to 8 c today the meridional warm pool expansion evidently had enormous impacts on the pliocene climate including a slowdown of the atmospheric hadley circulation and el nino like conditions in the equatorial region ultimately sustaining a climate state with weak tropical sea surface temperature gradients may require additional mechanisms of ocean heat uptake such as enhanced ocean vertical mixing

formal ratification of the quaternary system period and the pleistocene series epoch with a base at 2 58 ma in june 2009 the executive committee of the international union of geological sciences iugs formally ratified a proposal by the international commission on stratigraphy to lower the base of the quaternary system period to the global stratotype section and point gssp of the gelasian stage age at monte san nicola sicily italy the gelasian until then had been the uppermost stage of the pliocene series epoch the base of the gelasian corresponds to marine isotope stage 103 and has an astronomically tuned age of 2 58 ma a proposal that the base of the pleistocene series epoch be lowered to coincide with that of the quaternary the gelasian gssp was also accepted by the iugs executive committee the gssp at vrica calabria italy which had hitherto defined the basal boundary of both the quaternary and the pleistocene remains available as the base of the calabrian stage age now the second stage of the revised pleistocene in ratifying these proposals the iugs has acknowledged the distinctive qualities of the quaternary by reaffirming it as a full system period correctly complied with the hierarchical requirements of the geological timescale by lowering the base of the pleistocene to that of the quaternary and fully respected the historical and widespread current usage of both the terms quaternary and pleistocene copyright 2009 john wiley sons ltd

rivers and loess the significance of long river transportation in the complex event sequence approach to loess deposit formation abstract rivers are essential for loess deposit formation river systems which relate directly to loess deposit formation include the danube and the rhine the mississippi and the missouri the thames and the medway the indus ganges and brahmaputra the dnepr don and volga the clutha mataura and rakaia new zealand rivers the yellow river rivers in south america siberian rivers flowing north the odra and the wisla between the mountains and the ice the syr darya and amu darya into the desert the contention is that rivers are not just important in major loess deposit formation they are mandatory necessary imperative obligatory essential indispensable requisite for a complete and satisfactory study of a loess deposit we need to know how the material is produced how it is transported and distributed across the landscape how intermediate deposits are formed how transportation provides the defining properties i e open structure collapsibility draping across the landscape and what may happen post deposition e g chernozemisation fragipan formation increased collapsibility etc if rivers are essential then it would appear that the british loess is probably alpine material delivered by the proto rhine and the polish loess is not derived from the ice sheet to the north but from the mountains to the south the lack of loess in canada is explained by the absence of suitable rivers the loess in russia and neighbouring countries can be classified as jefferson et al jefferson i f evstatiev d karastenev d mavlyanova n g smalley i j 2003b the engineering geology of loess and loess like deposits a commentary on the russian literature engineering geology 68 333 351 suggested on the basis of associated rivers a new deposit of glacial loess is recognised associated with the dnepr don and volga rivers the uswr loess the smalley leach smalley i j leach j a 1978 the origin and distribution of the loess in the danube basin and associated regions of east central europe a review sedimentary geology 21 1 26 available from www geo edu ro sgr mod downloads pdf smalley sedgeo 1978 pdf vision of the loess in the danube basin and east central europe is probably misconceived they assigned a great significance to glacial action and put loess in a northern band it appears that this proposed glacial influence is minimal and that the danube loess is essentially mountain loess derived from the alps the carpathians the sudeten mountains and other high regions the danube system is a classic example of a river controlling loess distribution

a global synthesis of the marine and terrestrial evidence for glaciation during the pliocene epoch abstract the pliocene climate is globally warm and characterised by high atmospheric carbon dioxide concentrations yet the terrestrial and marine scientific communities have gathered considerable evidence for substantial glaciation events in both the northern and southern hemisphere prior to the quaternary evidence on land is fragmentary but marine records of glaciation present a more complete history of pliocene glaciation here we present a global compilation of the terrestrial and marine glacial evidence for the pliocene and demonstrate four glaciation events that can be identified in the southern and or northern hemisphere prior to the latest pliocene intensification of northern hemisphere glaciation there are two globally recognisable glacial events in the early pliocene c 4 9 4 8 ma and c 4 0 ma one event around the early late pliocene transition c 3 6 ma and one event during marine isotope stage m2 c 3 3 ma long term climate cooling decreasing carbon dioxide concentrations in the atmosphere and high climate sensitivity in the pliocene probably facilitated each glaciation event however the mechanisms behind the early pliocene glacial events are unclear the global glaciation at c 3 3 ma may be caused by changes in ocean gateways whereas the decline in carbon dioxide concentrations is important for the latest pliocene intensification of northern hemisphere glaciation

late pliocene greenland glaciation controlled by a decline in atmospheric co2 levels it is thought that the northern hemisphere experienced only ephemeral glaciations from the late eocene to the early pliocene epochs about 38 to 4 million years ago and that the onset of extensive glaciations did not occur until about 3 million years ago several hypotheses have been proposed to explain this increase in northern hemisphere glaciation during the late pliocene here we use a fully coupled atmosphere ocean general circulation model and an ice sheet model to assess the impact of the proposed driving mechanisms for glaciation and the influence of orbital variations on the development of the greenland ice sheet in particular we find that greenland glaciation is mainly controlled by a decrease in atmospheric carbon dioxide during the late pliocene by contrast our model results suggest that climatic shifts associated with the tectonically driven closure of the panama seaway with the termination of a permanent el nino state or with tectonic uplift are not large enough to contribute significantly to the growth of the greenland ice sheet moreover we find that none of these processes acted as a priming mechanism for glacial inception triggered by variations in the earth s orbit

shifts in north atlantic planktic foraminifer biogeography and subtropical gyre circulation during the mid piacenzian warm period abstract the mid piacenzian mp warm period 3 264 3 025 ma has been identified as the most recent time in geologic history during which mean global surface temperatures were considerably warmer than today for a sustained period this interval has therefore been proposed as a potential albeit imperfect analog for future climate change and as such has received much scientific attention over the past two decades central to this research effort is the pliocene research interpretation and synoptic mapping prism project an iterative paleoenvironmental reconstruction of the mp focused on increasing our understanding of warm period climate forcings dynamics and feedbacks by providing three dimensional data sets for general circulation models a mainstay of the prism project has been the development of a global sea surface temperature sst data set based primarily upon quantitative analyses of planktic foraminifer assemblages supplemented with geochemical sst estimates wherever possible in order to improve spatial coverage of the prism faunal data set in the low and mid latitude north atlantic this study provides a description of the mp planktic foraminifer assemblage from five ocean drilling program sites 951 958 1006 1062 and 1063 in the subtropical gyre a region critical to atlantic ocean circulation and tropical heat advection assemblages from each core provide evidence for a temperature and circulation driven 5 10 northward displacement of mp faunal provinces as well as regional shifts in planktic foraminifer populations linked to species ecology and interactions general biogeographic trends also indicate that relative to modern conditions gyre circulation was stronger particularly the gulf stream north atlantic current and north equatorial current and meridionally broader a comparison of mid piacenzian and modern north atlantic planktic foraminifer assemblages suggests that low latitude western boundary currents were less than 1 c warmer while eastern boundary currents were 1 2 c warmer supporting the hypothesis of enhanced northward heat advection along western boundary currents and warming of high latitude northeast atlantic source regions for the canary current these findings are consistent with a model of reduced meridional sst gradients with little to no low latitude warming and more vigorous ocean circulation results therefore support the theory that enhanced meridional overturn circulation and associated northward heat advection made an important contribution in conjunction with elevated atmospheric co2 concentrations to the 2 3 c global surface temperature increase relative to today and strong polar amplification of sst warmth during the mp warm period

a mechanism for freshening the caribbean sea in pre ice age time many believe that the central american seaway closed near 4 ma and that that closure led to increased salinity in the caribbean sea and stronger meridional overturning circulation in the atlantic which facilitated the waxing and waning of ice sheets in the northern hemisphere we offer an alternative explanation for caribbean salinification the atmosphere transports approximately 0 23 sv 1 sv 106 m3s 1 of fresh water moisture from the caribbean to the pacific today but that amount varies by 20 during el nino southern oscillation events regressions of moisture transport against the nino 3 index a measure of the sea surface temperature in the eastern tropical pacific show less moisture transport from the caribbean during el nino events than average abundant evidence indicates that at 3 4 ma the eastern tropical pacific was 3 5 4 c warmer than today and if so an extrapolation of such regressions suggests that smaller moisture transport across central america might account for paleoceanographic inferences of a smaller salinity difference between the caribbean and pacific at that time accordingly that decreased salinity difference at 3 4 ma would not require blockage of relatively fresh pacific water at 2 4 ma by the closure of the central american seaway but rather would be consistent with a transition from el nino to la nina like conditions in the eastern tropical pacific around that time

mapping bathymetry and depositional facies on great bahama bank satellite imagery and an extensive set of water depth measurements have been used to map and critically evaluate the magnitude and patterns of bathymetry across great bahama bank descriptions of previously collected sediment samples were combined with satellite imagery to map and refine the interpreted distribution of surficial carbonate sediments depositional facies data reveal that 60 of great bahama bank lies in 5 m or less of water the deep portion occurs mainly in a generally east west trending area in the southern portion of the platform the re evaluation of the facies reveals that great bahama bank is essentially a very grainy platform with muddier accumulations primarily in the lee of andros island this area of great bahama bank also experiences currents related to an excursion of the florida current onto the platform top possibly enhancing sediment mud production through the generation of whitings sediment equivalents to mudstones wackestones and mud rich packstones cover 8 5 and 14 respectively of the platform top whereas sediment equivalents to mud poor packstones grainstones and rudstones account for 20 45 and 3 of the surface area boundstones reefs were not specifically mapped in this study due to the resolution of the mapping there is a poor relationship between the occurrence of the depositional texture and water depth in that the grainier sediment types are abundant across the full range of water depths the most abrupt lateral facies changes portrayed on the facies maps are observed leeward of islands areas which also hold the highest diversity in facies type the majority of the islands on the platform align with the north west south east strike of the platform margin and these islands in turn exert control on the shape and orientation of facies belts that develop in proximity to them for this reason regions of the platform that contain principal islands host facies belts that align with the principal axis of the platform whereas for regions lacking islands the facies belts adopt an east west trend consistent with prevailing winds and currents there is a clear trend that the wide southern portion of the platform hosts the most continuous expanses of grain rich sediments

orbital driven environmental changes recorded at odp site 959 eastern equatorial atlantic from the late miocene to the early pleistocene palaeorecords from tropical environments are important to explore the linkages between precipitation atmospheric circulation and orbital forcing in this study new high resolution xrf data from odp site 959 3 37 n 2 44 w have been used to investigate the relationship between palaeoenvironmental changes in west africa and sedimentation in the tropical east atlantic ocean iron intensity data have been used to build a 91 m composite depth record that has been astronomically tuned allowing the development of a detailed age model from 6 2 to 1 8 ma based on this new stratigraphy we studied the variations of ti al ti ca and al si ratios proxies for aeolian versus fluvial supply as dust indicator and fine versus coarse grain size respectively we discuss sedimentation patterns at odp site 959 associated with the environmental changes from the late miocene until the early pleistocene during the interval corresponding to the earlier stages of the messinian salinity crisis our proxy records indicate enhanced run off from the west african continent and major supply of fine material at odp site 959 suggesting a stronger monsoon and increased precipitation during eccentricity minima a long term decrease of river supply is documented after 5 4 ma until the end of the pliocene from the increased values and variability of ti al and ti ca ratios we suggest that after 3 5 ma dust started to reach the study site probably as a result of the southward shift of the intertropical convergence zone during winter between 3 2 and 2 9 ma odp site 959 ti ca ratios exhibit three maxima corresponding to eccentricity maxima similarly to other dust records of northern africa this suggests continent wide aridity or larger climate variability during that interval eccentricity forcing 405 and 100 kyr and precession frequencies are found in the entire studied interval the variations of ti al ratio suggest stronger seasonality between 5 8 and 5 5 ma and after 3 2 ma

el nino southern oscillation pliocene climate and equifinality it has been suggested that during the pliocene ca 5 1 8ma an el nino state existed as a permanent rather than an intermittent feature that is the tropical pacific ocean was characterized by a much weaker east west gradient than today one line of inquiry used to investigate this idea relates modern el nino teleconnections to pliocene proxy data by comparing regional differences in precipitation and surface temperature with climate patterns associated with present day el nino events assuming that agreement between pliocene data and observations of modern el nino events supports this interpretation here we examine this assumption by comparing outputs from a suite of mid pliocene climate simulations carried out with the uk met office climate model regional patterns of climate change associated with changes in model boundary conditions are compared with observed el nino southern oscillation teleconnection patterns our results indicate that many of the proposed permanent el nino surface temperature and precipitation patterns are observable in mid pliocene climate simulations even when they display variability in tropical pacific sea surface temperatures ssts or when forced with a modern east west sst gradient our experiments highlight the possibility that the same outcome may be achieved through different initial conditions equifinality an important consideration for reconstructed patterns of regional mid pliocene climate

the evolution of the equatorial thermocline and the early pliocene el padre mean state the tropical pacific thermocline strength depth and tilt are critical to tropical mean state and variability during the early pliocene 3 5 to 4 5 ma the eastern equatorial pacific eep thermocline was deeper and the cold tongue was warmer than today which resulted in a mean state with a reduced zonal sea surface temperature gradient or el padre however it is unclear whether the deep thermocline was a local feature of the eep or a basin wide condition with global implications our measurements of mg ca of globorotalia tumida in a western equatorial pacific site indicate pliocene subsurface temperatures warmer than today thus el padre included a basin wide thermocline that was relatively warm deep and weakly tilted at 4 ma thermocline steepening was coupled to cooling of the cold tongue since 4 ma the basin wide thermocline cooled shoaled gradually with implications for thermocline feedbacks in tropical dynamics and the interpretation of tex86 derived temperatures

caco3 precipitation kinetics in waters from the great bahama bank implications for the relationship between bank hydrochemistry and whitings the source of whitings on the great bahama bank and their relationship to major changes in the chemistry of bank waters have been among the longest and most hotly debated topics in carbonate geochemistry in this paper we demonstrate that the reaction kinetics of calcite with bank waters for a given saturation state are similar to but somewhat slower 2 to 3 times than with gulf stream water the interpretation of the reaction kinetics of suspended bank sediment with bank water requires that the precipitating phase be about twice as soluble as aragonite good agreement at equivalent saturation states was found between experimental precipitation rates and those calculated for the rate of change of bank water chemistry in the region of whitings these results indicate that the dominant mode of carbonate removal is via precipitation on resuspended sediments rather than the rapid pseudo homogeneous precipitation of calcium carbonate in the water column resulting in the formation of a whiting estimates indicate that single aragonite needles may be resuspended many times over a period of decades during which they experience repeated overgrowth a major portion 98 of suspended calcium carbonate is outside the visually dramatic whitings thus as visually spectacular as they are whitings do not represent a short term locally massive precipitation of carbonate on the great bahama bank nor are they even likely to be the dominant sites of carbonate removal in this region although future refinements are needed that include seafloor processes we have at this point arrived at a mechanistic kinetic model that provides a reasonably quantitative explanation for the hydrochemistry of the carbonate system on the northern great bahama bank

evolution of the eastern tropical pacific through plio pleistocene glaciation a tropical pacific climate state resembling that of a permanent el nino is hypothesized to have ended as a result of a reorganization of the ocean heat budget 3 million years ago a time when large ice sheets appeared in the high latitudes of the northern hemisphere we report a high resolution alkenone reconstruction of conditions in the heart of the eastern equatorial pacific eep cold tongue that reflects the combined influences of changes in the equatorial thermocline the properties of the thermocline s source waters atmospheric greenhouse gas content and orbital variations on sea surface temperature sst and biological productivity over the past 5 million years our data indicate that the intensification of northern hemisphere glaciation 3 million years ago did not interrupt an almost monotonic cooling of the eep during the plio pleistocene sst and productivity in the eastern tropical pacific varied in phase with global ice volume changes at a dominant 41 000 year obliquity frequency throughout this time changes in the southern hemisphere most likely modulated most of the changes observed

simulating pliocene warmth and a permanent el nino like state the role of cloud albedo available evidence suggests that during the early pliocene 4 5 ma the mean east west sea surface temperature sst gradient in the equatorial pacific ocean was significantly smaller than today possibly reaching only 1 2 c the meridional sst gradients were also substantially weaker implying an expanded ocean warm pool in low latitudes subsequent global cooling led to the establishment of the stronger modern temperature gradients given our understanding of the physical processes that maintain the present day cold tongue in the east warm pool in the west and hence sharp temperature contrasts determining the key factors that maintained early pliocene climate still presents a challenge for climate theories and models this study demonstrates how different cloud properties could provide a solution we show that a reduction in the meridional gradient in cloud albedo can sustain reduced meridional and zonal sst gradients an expanded warm pool and warmer thermal stratification in the ocean and weaker hadley and walker circulations in the atmosphere having conducted a range of hypothetical modified cloud albedo experiments we arrive at our pliocene simulation which shows good agreement with proxy sst data from major equatorial and coastal upwelling regions the tropical warm pool middle and high latitudes and available subsurface temperature data as suggested by the observations the simulated pliocene like climate sustains a robust el nino southern oscillation despite the reduced mean east west sst gradient our results demonstrate that cloud albedo changes may be a critical element of pliocene climate and that simulating the meridional sst gradient correctly is central to replicating the geographical patterns of pliocene warmth

the matuyama brunhes boundary in loess sections in the south of the east european plain and their correlation on the basis of palaeomagnetic and palaeopedologic data abstract the matuyama brunhes boundary mbb in loess sections of the east european plain one of the greatest areas of global loess distribution is a highly debatable issue the ambiguity of the mbb position here results from the complexity of loess soil magnetization processes and an apparent delay in loess remanence acquisition and from the uncertainties of pedostratigraphic interpretations in the don glaciation area the mbb is unanimously placed below the don moraine although the exact position is still controversial in the sites of the northern azov sea the mbb is however placed in the loess horizon considered to be the equivalent of the don moraine in the north the inconsistency of this interpretation is demonstrated by detailed magnetostratigraphic and pedostratigraphic studies in the western sites of zaporozh e dnieper basin novaya etuliya lower danube basin and roxolany lower dniester basin in all these sites albeit with certain minor discrepancies the mbb is found two or three interglacial palaeosols below the don loess which is overlain by the good stratigraphic marker of the vorona pedocomplex a thick polygenetic red brown palaeosol formed supposedly in a mediterranean climate here the mbb is placed in a quadruple soil unit termed roxolany loess soil suite which consists of four closely spaced strongly calcareous soils occupying an interval between the don loess on top and the earlier well developed bobrov loess with reversed matuyama magnetization the roxolany suite can possibly be correlated with the three palaeosols of the pre don ilyinka unit of the russian unified stratigraphic scheme and thus confirms the interpretation of the mbb in the central areas of the east european plain as to the interval between the ternovka second pre don palaeosol and the troitsk third pre don palaeosol

late miocene decoupling of oceanic warmth and atmospheric carbon dioxide forcing measurements from several ocean cores reveal that ocean warmth persisted throughout the late miocene epoch despite co2 levels of only 200 350 p p m v probably driven by a deep thermocline that isolated climate responses from co2 variations geological records of past climate provide the only opportunity to investigate earth s response to large variations in atmospheric carbon dioxide concentrations during the late miocene between 12 million and 5 million years ago atmospheric co2 levels of only 200 to 350 parts per million by volume were accompanied by almost ice free conditions in the northern hemisphere and the continents were warmer than they are at present raising questions about the persistence of co2 climate couplings using measurements from several ocean cores lariviere et al show that ocean warmth persisted throughout the late miocene probably driven by a thick thermocline that isolated climate responses from co2 variations as the depth of the thermocline declined during the late miocene the more familiar relationship between co2 and climate was established deep time palaeoclimate studies are vitally important for developing a complete understanding of climate responses to changes in the atmospheric carbon dioxide concentration that is the atmospheric partial pressure of co2 1 although past studies have explored these responses during portions of the cenozoic era the most recent 65 5 million years myr of earth history comparatively little is known about the climate of the late miocene 12 5 myr ago an interval with values of only 200 350 parts per million by volume but nearly ice free conditions in the northern hemisphere2 3 and warmer than modern temperatures on the continents4 here we present quantitative geochemical sea surface temperature estimates from the miocene mid latitude north pacific ocean and show that oceanic warmth persisted throughout the interval of low 12 5 myr ago we also present new stable isotope measurements from the western equatorial pacific that in conjunction with previously published data5 6 7 8 9 10 reveal a long term trend of thermocline shoaling in the equatorial pacific since 13 myr ago we propose that a relatively deep global thermocline reductions in low latitude gradients in sea surface temperature and cloud and water vapour feedbacks may help to explain the warmth of the late miocene additional shoaling of the thermocline after 5 myr ago probably explains the stronger coupling between sea surface temperatures and climate that is characteristic of the more recent pliocene and pleistocene epochs11 12

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

an approach to the problem of loess deposit formation some comments on the in situ or soil eluvial hypothesis abstract the problem of loess formation has been widely discussed for a long time and in many languages at the beginning of the 21st century some parts of this debate are still going on a case is still being made for the in situ approach and there are problems of terminology and mechanism for the central asian loess consideration of the origin of loess material has now replaced the discussion on deposit formation as the major intrinsic problem and in the world of ground engineering there is still much investigation on the origins of collapsibility which is in effect a discussion of loess origins there remain some interesting and useful observations to be made on the north african loess and the loess like materials in australia and the desert loess controversy is still running connections of loess to chernozems fragipans and rendzinas are becoming clearer and it seems that it may be possible to appreciate a loess landscape in which the loess contribution is not immediately apparent recent sem observations suggest that collapsibility develops after metastability as the in situ theory appears to imply

controls on morphology and sedimentology of carbonate tidal deltas abacos bahamas abstract although the physical processes controlling siliciclastic shoal bodies are reasonably well understood the sedimentary processes that shape carbonate tidal shoal systems are poorly constrained the tidal deltas of the northwestern abaco islands bahamas provide a unique opportunity to explore the relationships between physical and sedimentary processes in a variety of sizes and shapes of tidal deltas the length of tidal deltas range in size from 350 m to 2 km from the inlet to the termination of the delta lobe and shoal crests consist primarily of well sorted ooid sands mean grain size between 400 and 500 m mcmanus sorting factor 0 70 coated grains are rare off the shoals and sorting decreases with distance from the shoal crests velocities in the rocky inlets can exceed 2 m s in the daily tidal cycles and the systematic distribution of grain types reflects tidal velocity variations areas with the highest velocities 0 80 m s correspond to hard rocky bottoms with some skeletal grains these regions of elevated velocities are focused within the inlets where jets of high velocity currents form during each tidal cycle these current jets extend outward from the inlet throat and velocities decrease outwards as the flow disperses velocities between 40 and 80 cm s occur in the regions with abundant ooids and peloids are most abundant in the lowest velocity regions the results of this study illustrate a clear relationship between quotidian physical processes and their geomorphic and sedimentologic products in a carbonate system in this context carbonates appear to share many geomorphic similarities with siliciclastic analogs the results represent an important step beyond qualitative facies interpretations and towards quantitative specified environmental and sedimentologic characterizations for carbonate systems

role of cenozoic progradation in evolution of great bahama bank the bahama banks have long been thought to have grown upward with only minor changes in the position of their margins instead new multichannel seismic profiles over the top of the northwestern great bahama bank reveal that progadation of some margins during the cenozoic nearly doubled the size of smaller nuclear platforms of the late cretaceous the smaller late cretaceous platforms were separated by seaways since then these platforms have grown vertically about 1500 m but some of their margins have prograded as much as 25 kmexclamation this progradation combined with high rates of accumulation in the seaways resulted in the coalescence of the small platforms into the present day configuration of the bank the prograding systems display different seismic characteristics suggesting various modes of bank margin migration rapid prograding systems are characterized by a series of complex sigmoid oblique sequences with toplap within the individual sequences steep slopes and reflection free spots at the edge of some of the sequences which are interpreted as reef buildups in shallow 500 m closed seaways lower energy systems occur characterized by sigmoidal prograding sequences along deep closed seaways parallel reflectors indicate the accretion along relatively steep slopes stationary margins are recognized on east facing windward margins more on northwestern great bahama bank progradation occurred preferentially on west facing leeward margins however in profiles from southern great bahama bank the direction of progradation varies and may be influenced more by circulation in the adjacent seaway than by the direction of the winds less

modelling pliocene warmth contribution of atmosphere oceans and cryosphere the relative role of the atmosphere oceans and cryosphere in contributing towards middle pliocene warmth ca 3 ma bp is investigated using the hadcm3 coupled ocean atmosphere general circulation model the model was initialised with boundary conditions from the usgs prism2 data set and a pliocene atmospheric co2 level of 400 ppmv and run for 300 simulated years the simulation resulted in a global surface temperature warming of 3degreesc compared to present day in contrast to earlier modelling experiments for the pliocene surface temperatures warmed in most areas including the tropics 1 5degreesc compared with present day the model predicts a general pattern of ocean warming 1 5degreesc in both hemispheres to a depth of 2000 m below which no significant differences are noted sea ice coverage is massively reduced up to 90 the flow of the gulf stream north atlantic drift is up to 100 mm s 1 greater in the pliocene case analysis of the model predicted meridional streamfunction suggests a global pattern of reduced outflow of antarctic bottom water aabw up to 5 sv a shallower depth for north atlantic deep water formation and weaker thermohaline circulation 3 sv the decrease in aabw occurs mainly in the pacific rather than atlantic ocean model diagnostics for heat transports indicate that neither the oceans nor the atmosphere are transporting significantly more heat in the pliocene scenario rather these results indicate that the major contributing mechanism to global pliocene warmth was the reduced extent of high latitude terrestrial ice sheets 50 reduction on greenland 33 reduction on antarctica and sea ice cover resulting in a strong ice albedo feedback these results highlight the need for further studies designed to improve our knowledge regarding pliocene terrestrial ice configurations

stratospheric modulation of the boreal response to pliocene tropical pacific sea surface temperatures variations in the sea surface temperature of the eastern equatorial pacific usually associated with the el nino southern oscillation have a global impact previous work has shown that the stratosphere modulates the northern hemisphere response to these temperature anomalies here we show that the stratosphere also plays a major role in modulating the response to tropical sea surface temperature anomalies representative of the mean state of the pliocene era approximately four million years ago key to the response is a predominance of sudden stratospheric warmings during boreal winter which cause a large anomalous surface pressure response over the north atlantic ocean the stratospheric modulation results in relatively cold winter spring eurasian surface temperatures and relatively warm surface temperatures in greenland and north america the implications of these results for simulating and understanding the climate of the pliocene era are discussed

permanent el nino like conditions during the pliocene warm period during the warm early pliocene 4 5 to 3 0 million years ago the most recent interval with a climate warmer than today the eastern pacific thermocline was deep and the average west to east sea surface temperature difference across the equatorial pacific was only 1 5 0 9 c much like it is during a modern el nino event thus the modern strong sea surface temperature gradient across the equatorial pacific is not a stable and permanent feature sustained el nino like conditions including relatively weak zonal atmospheric walker circulation could be a consequence of and play an important role in determining global warmth

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

impact of mountains on tropical circulation in two earth system models abstracttwo state of the art earth system models esms were used in an idealized experiment to explore the role of mountains in shaping earth s climate system similar to previous studies removing mountains from both esms results in the winds becoming more zonal and weaker indian and asian monsoon circulations however there are also broad changes to the walker circulation and el nino southern oscillation enso without orography convection moves across the entire equatorial indo pacific basin on interannual time scales enso has a stronger amplitude lower frequency and increased regularity a wider equatorial wind zone and changes to equatorial wind stress curl result in a colder cold tongue and a steeper equatorial thermocline across the pacific basin during la nina years anomalies associated with enso warm events are larger without mountains and have greater impact on the mean tropical climate than when mountains are present without mountains the centennial mean pacific walker circulation wea

pliocene pleistocene evolution of sea surface and intermediate water temperatures from the southwest pacific over the last 5 million years the global climate system has evolved toward a colder mean state marked by large amplitude oscillations in continental ice volume equatorward expansion of polar waters and strengthening temperature gradients have been detected however the response of the mid latitudes and high latitudes of the southern hemisphere is not well documented despite the potential importance for climate feedbacks including sea ice distribution and low high latitude heat transport here we reconstruct the pliocene pleistocene history of both sea surface and antarctic intermediate water aaiw temperatures on orbital time scales from deep sea drilling project site 593 in the tasman sea southwest pacific we confirm overall pliocene pleistocene cooling trends in both the surface ocean and aaiw although the patterns are complex the pliocene is warmer than modern but our data suggest an equatorward displacement of the subtropical front relative to present and a poleward displacement of the subantarctic front of the antarctic circumpolar current acc two main intervals of cooling from 3 ma and 1 5 ma are coeval with cooling and ice sheet expansion noted elsewhere and suggest that equatorward expansion of polar water masses also characterized the southwest pacific through the pliocene pleistocene however the observed trends in sea surface temperature and aaiw temperature are not identical despite an underlying link to the acc and intervals of unusual surface ocean warmth 2 ma and large amplitude variability in aaiw temperatures from 1 ma highlight complex interactions between equatorward displacements of fronts associated with the acc and or varying poleward heat transport from the subtropics

el nino s tropical climate and teleconnections as a blueprint for pre ice age climates 1 at 2 7 million years ago the warm equable climates of early and middle pliocene time used here to mean from 5 to 2 7 ma were replaced by recurring ice ages most attempts to explain the change appeal either to changes in co2 in the atmosphere or reduced heat transport by the atlantic ocean the sources of the strongest teleconnections in the current climate however lie in the tropics and such connections occur by transport of heat and moisture by the atmosphere the most prominent of these teleconnections link aberrations in sea surface temperatures in the equatorial pacific el nino southern oscillation enso variations with warm and dry or cool and wet anomalies in extratropical climates we show that in most cases early and middle pliocene climate both in equatorial regions and in the extratropics differ from present day climates with the same spatial pattern as that associated with enso for instance not only was canada warmer during early pliocene time than at present as it is during el nino but the region surrounding the gulf of mexico appears to have been cooler and a bit wetter as it commonly is during el nino a virtually permanent el nino like state appears to have characterized pre ice age climates suggesting that transport of heat by the atmosphere was the principal mechanism that maintained extratropical warmth accordingly cooling and the growth of recurring ice sheets in the northern hemisphere resulted from the development of a strong walker circulation and a weakening of the hadley circulation

miocene to pliocene development of surface and subsurface temperatures in the benguela current system 1 the initiation of the benguela upwelling has been dated to the late miocene but estimates of its sea surface temperature evolution are not available this study presents data from ocean drilling program odp site 1085 recovered from the southern cape basin samples of the middle miocene to pliocene were analyzed for alkenone based u37k sstuk and glycerol dialkyl glycerol tetraether gdgt based tex86 temptex water temperature proxies in concordance with global cooling during the miocene sstuk and temptex exhibit a decline of about 8 c and 16 c respectively the temperature trends suggest an inflow of cold antarctic waters triggered by antarctic ice sheet expansion and intensification of southern hemisphere southeasterly winds a temperature offset between both proxies developed with the onset of upwelling which can be explained by differences in habitat alkenone producing phytoplankton live in the euphotic zone and record sea surface temperatures while gdgt producing thaumarchaeota are displaced to colder subsurface waters in upwelling influenced areas and record subsurface water temperatures we suggest that variations in subsurface water temperatures were driven by advection of cold antarctic waters and thermocline adjustments that were due to changes in north atlantic deep water formation a decline in surface temperatures an increased offset between temperature proxies and an increase in primary productivity suggest the establishment of the benguela upwelling at 10 ma during the messinian salinity crisis between 7 and 5 ma surface and subsurface temperature estimates became similar likely because of a strong reduction in atlantic overturning circulation while high total organic carbon contents suggest a biogenic bloom in the pliocene the offset between the temperature estimates and the cooling trend was reestablished

tectonic uplift and eastern africa aridification the history of eastern african hominids has been linked to a progressive increase of open grassland during the past 8 million years this trend was explained by global climatic processes which do not account for the massive uplift of eastern african topography that occurred during this period atmosphere and biosphere simulations quantify the role played by these tectonic events the reduced topographic barrier before 8 million years ago permitted a zonal circulation with associated moisture transport and strong precipitation our results suggest that the uplift itself led to a drastic reorganization of atmospheric circulation engendering the strong aridification and paleoenvironmental changes suggested by the data

dominant control of the south asian monsoon by orographic insulation versus plateau heating heat emitted from the tibetan plateau as dry heat and water vapour has long been assumed to be the main driver of the south asian summer monsoon but new work suggests that in fact it is the neighbouring mountains that are the major influence william boos and zhiming kuang use an atmospheric model to show that flattening the tibetan plateau has little effect on the monsoon so long as the himalayas and surrounding mountain ranges remain the plateau does boost rainfall locally along its southern edge but it is the build up of hot moist air over india insulated from colder drier air by the himalayas that drives large scale monsoon circulation the elevation of the tibetan plateau is thought to cause its surface to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales here however an atmospheric model is used to show that flattening of the tibetan plateau has little effect on the monsoon provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved the tibetan plateau like any landmass emits energy into the atmosphere in the form of dry heat and water vapour but its mean surface elevation is more than 5 km above sea level this elevation is widely held to cause the plateau to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales1 2 3 4 5 observations of the present climate however do not clearly establish the tibetan plateau as the dominant thermal forcing in the region peak upper tropospheric temperatures during boreal summer are located over continental india south of the plateau here we show that although tibetan plateau heating locally enhances rainfall along its southern edge in an atmospheric model the large scale south asian summer monsoon circulation is otherwise unaffected by removal of the plateau provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved additional observational and model results suggest that these mountains produce a strong monsoon by insulating warm moist air over continental india from the cold and dry extratropics these results call for both a reinterpretation of how south asian climate may have responded to orographic uplift and a re evaluation of how this climate may respond to modified land surface and radiative forcings in coming decades

large scale hydrological change drove the late miocene c4 plant expansion in the himalayan foreland and arabian peninsula carbon isotope changes in paleosols from siwalik pakistan and marine sediments from the bengal fan indicate a major c 4 plant expansion in the himalayan foreland during the late miocene however the timing and mechanisms behind the c 4 plant expansion remain enigmatic here we present high resolution 60 k y biomarker and compound specific isotope data spanning the past 11 m y from ocean drilling program site 722 in the arabian sea an 5 6 increase in leaf wax 13 c values indicates a marked rise of c 4 plants from 10 to 5 5 ma with accelerated expansion from 7 9 to 5 5 ma a concurrent 50 rise in leaf wax d values is attributed to a combined effect of changes in precipitation amount and evaporation indicating that source regions for the plant waxes became progressively drier from 10 to 5 5 ma in contrast to earlier reports our isotope records biomarker abundances alkenone u k 37 and globigerina bulloides abundance data do not suggest enhanced summer monsoon circulation during this time interval rather our results suggest that large scale hydrological changes drove the late miocene expansion of c 4 plants in the himalayan foreland and arabian peninsula

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

a permanent el nino like state during the pliocene the pliocene may have been characterized by permanent el nino like conditions initial modeling studies suggest that this may have contributed to pliocene warmth the termination of this state may have influenced northern hemisphere glaciation nhg we use the hadley centre coupled model version 3 to examine the role of the oceans and ocean structure on pliocene warmth a permanent el nino like state is not predicted annual mean sea surface temperatures in the eastern equatorial pacific at ocean drilling program sites 847 and 851 increase by 1 71 c and 1 15 c respectively however el nino southern oscillation events are clearly expressed by the model sensitivity tests indicate that a prescribed permanent el nino like condition increases annual global mean surface temperatures by a maximum of 0 6 c if the pliocene was characterized by such a condition it is questionable that it provided a major contribution to global warmth and therefore unlikely that the termination of this state contributed significantly to the onset of nhg

sensitivity of mass balance of five swiss glaciers to temperature changes assessed by tuning a degree day model a degree day model is used to assess the sensitivity of the mass balance of five swiss glaciers to temperature changes the model uses temperature data extrapolated from nearby climate stations and is tuned by varying precipitation to make the model fit the observed distribution of mass balance with altitude once the model is tuned the effect of temperature change is simulated by recalculating the mass balance with the same parameters as before but with a temperature increase of 1 c throughout the year the largest mass balance changes involving increased ablation of 1 m w e a 1 c 1 occur at the snout with a progressively smaller increase with altitude the area averaged sensitivities for the five glaciers are 0 7 to 0 9 m w e a 1 c 1 if annual precipitation also increased by 20 it would partly offset the effect of the 1 c higher temperatures but could not compensate for it

relative importance of meridional and zonal sea surface temperature gradients for the onset of the ice ages and pliocene pleistocene climate evolution sst gradients and ice ages

role of tropics in changing the response to milankovich forcing some three million years ago appeared in regions that today have intense oceanic upwelling the eastern equatorial pacific and the coastal zones of southwestern africa and california there was furthermore a significant change in the earth s response to milankovich forcing obliquity signals became large but those associated with precession and eccentricity remained the same the latter change in the earth s response can be explained by hypothesizing that the global cooling during the cenozoic affected the thermal structure of the ocean it caused a gradual shoaling of the thermocline around 3 ma the thermocline was sufficiently shallow for the winds to bring cold water from below the thermocline to the surface in certain upwelling regions this brought into play feedbacks involving

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

on the role of sea surface temperature gradients in forcing low level winds and convergence in the tropics abstract we examine the importance of pressure gradients due to surface temperature gradients to low level p 700 mb flow and convergence in the tropics over time scales 1 month the latter plays a crucial role in determining the distribution of cumulonimbus convection and rainfall our approach is to consider a simple one layer model of the trade cumulus boundary layer wherein surface temperature gradients are mixed vertically consistent with ecmwf analyzed data the top of the layer is taken at 700 mb the influence from higher levels is intentionally suppressed by setting horizontal pressure gradients and frictional stresses to zero at the top of the layer horizontal convergence within the layer is taken up by cumulonimbus mass flux however the development of the cumulonimbus mass flux is associated with a short relaxation time o hr roughly the development time for such convection during this short time horizontal convergence acts to redistribute mass so as to reduce horizontal pressur

the relationship between wet bulk density and carbonate content in sediments from the eastern equatorial pacific abstract sediment cores collected from the eastern equatorial pacific ocean display a clear positive second order relationship between wet bulk density wbd and carbonate content this has long interested the paleoceanography community because detailed gamma ray attenuation porosity evaluator grape measurements which approximate wbd might be used to determine records of carbonate content at very high temporal resolution although general causes for the relationship are known they have not been presented and discussed systematically on the basis of first principles in this study we measure the mass and carbonate content of 50 sediment samples with known wbd from site u1338 before and after rinsing with de ionized water we also determine the mass related proportion of coarse 63 m material samples exhibit clear relationships between wbd carbonate content mass loss upon rinsing and grain size we develop a series of mathematical expressions to describe these relationships and solve them numerically as noted by previous workers the second order relationship between wbd and carbonate content results from the mixing of biogenic carbonate and biogenic silica which have different grain densities and different porosities however at high carbonate content a wide range in wbd occurs because samples with greater amounts of coarse carbonate have higher porosity moreover compaction impacts carbonate particles more than biogenic silica particles as such a single two component equation cannot be used to determine carbonate content accurately across depth intervals where both the porosity and type of carbonate vary instead the wbd carbonate relationship is described by an infinite series of curves each which represents mixing of multiple sediment components with different densities and porosities dissolved ions also precipitate from pore space during sample drying which adds mass to the sediment without rinsing samples simple empirical relationships between wbd and carbonate content are further skewed by salt dilution

late pliocene to early pleistocene changes in the north atlantic current and suborbital scale sea surface temperature variability the strength and latitudinal position of the north atlantic current nac determines the position of the arctic front and heat transport to the high northern latitudes with potentially important consequences for northern hemisphere glaciation a southward shift in the nac and reduced poleward heat transport is hypothesized to have triggered the last major climate transition in earth s history late pliocene intensification of northern hemisphere glaciation inhg in turn inhg is hypothesized to have led to the amplification of climate variability on suborbital time scales to date however only a handful of adequately resolved records are available to test these two hypotheses here we present a new late pliocene to earliest pleistocene record from integrated ocean drilling program site u1313 north atlantic 41 n 2 9 to 2 4 ma we use mg ca derived paleotemperature records in planktic foraminiferal calcite to investigate changes in summer sea surface temperatures sst on orbital and suborbital time scales our results call into question the suggestion that significant weakening and or southward shift of the nac served as a trigger for northern hemisphere cooling and intensified continental ice sheet growth across inhg in contrast to the late pleistocene during inhg we find that the position of the nac and arctic front probably lay well to the north of site u1313 and that the amplitude of suborbital sst variability did not change on glacial interglacial time scales conservative estimates of late pliocene to earliest pleistocene interglacial summer ssts in our record are up to 3 c warmer than present while glacial summer ssts are only 2 c to 3 c cooler in fact our interglacial summer ssts are remarkably similar to those of the mid pliocene our findings indicate that inhg must have involved amplifying feedback mechanisms that are tightly coupled to ice sheet growth but that these processes were insufficiently developed by the late pliocene earliest pleistocene to have triggered large amplitude changes in suborbital climate in the midlatitude north atlantic

a deep eastern equatorial pacific thermocline during the early pliocene warm period abstract during the early pliocene warm period 4 6 4 2 ma in the eastern equatorial pacific upwelling region sea surface temperatures were warm in comparison to modern conditions warm upwelling regions have global effects on the heat budget and atmospheric circulation and are argued to have contributed to pliocene warmth though warm upwelling regions could be explained by weak winds and or a deep thermocline the temporal and spatial evolution of the equatorial thermocline is poorly understood here we reconstruct temporal and spatial changes in subsurface temperature to monitor thermocline depth and show the thermocline was deeper during the early pliocene warm period than it is today we measured subsurface temperature records from eastern equatorial pacific odp transect sites 848 849 and 853 using mg ca records from globorotalia tumida which has a depth habitat of 50 100 m in the early pliocene subsurface temperatures were 4 5 c warmer than modern temperatures indicating the thermocline was relatively deep subsurface temperatures steeply cooled 2 3 c from 4 8 to 4 0 ma and continued to cool an additional 2 3 c from 4 0 ma to present compared to records from other regions the data suggests the pronounced subsurface cooling between 4 8 and 4 0 ma was a regional signal related to restriction of the isthmus of panama while continued cooling from 4 0 ma to present was likely related to global processes that changed global thermocline structure additionally the spatial evolution of the equatorial thermocline along a n s transect across odp sites 853 849 and 848 suggests an intensification of the southeast trades from the pliocene to present large scale atmospheric and oceanographic circulation processes link high and low latitude climate through their influence on equatorial thermocline source water regions and consequently the equatorial thermocline through these low latitude high latitude linkages changes in the equatorial thermocline and thermocline source water played an important role in the transition from the warm pliocene to the cold pleistocene

cooling and drying in northeast africa across the pliocene abstract terrestrial records suggest that northeast africa experienced drying during the pliocene however these records are often incomplete in time and space and questions about this shift in climate remain here we use marine sediments from deep sea drilling project dsdp site 231 in the gulf of aden to generate a multi proxy organic geochemical record of northeast african climate spanning 5 3 2 ma this new record provides a regional perspective on climate and serves as context for the fossil record of early hominin evolution we measured leaf wax carbon 13cwax and hydrogen dwax isotopic composition and tex86 tetraether index of 86 carbons to investigate past changes in vegetation aridity and ocean temperature respectively in the earliest pliocene we infer warm subsurface ocean temperatures from tex86 semi arid conditions on land and extensive c4 grasslands based on dwax 13cwax and previously published pollen after 5 ma ocean temperatures gradually cooled and at 4 3 ma there was a transition to arid conditions on land based on dwax and pollen grasslands yielded to a mid pliocene landscape of dry shrublands this drying appears to be an atmospheric response to cooling ocean temperatures which may reflect changes in tropical ocean circulation the intensification of indian monsoon winds or perhaps other changes associated with pliocene cooling

warm upwelling regions in the pliocene warm period 1 given the importance of upwelling processes to coastal productivity and regional climate it is critical to study the role of upwelling regions within the context of global climate change we generated sea surface temperature sst records for the last 5 million years in three important upwelling regions the eastern equatorial pacific the california margin and the peru margin prior to 3 0 ma ssts at all sites were significantly warmer than today by 3 9 c indicating that cold upwelling regions that characterize the modern pacific ocean did not exist in the early pliocene warm period 4 6 to 3 1 ma earth s most recent period of sustained global warmth alkenone phosphorus and organic carbon mass accumulation rate records indicate that changes in productivity and sst were decoupled and that upwelling of nutrient enriched water occurred even when ssts were warm during the early pliocene thus the long term trends in sst are likely explained by changes in the temperature of upwelled water rather than in the strength of upwelling favorable winds alone the fact that gradual cooling of upwelling regions began before the onset of significant northern hemisphere glaciation provides further evidence that the growth of ice sheets and their influence on atmospheric winds alone can not explain the cooling of upwelling regions our results suggest that the long term average ssts of upwelling regions are influenced by global changes in the depth and or temperature of the ventilated thermocline

the role of co2 decline for the onset of northern hemisphere glaciation the pliocene pleistocene transition ppt from around 3 2 to 2 5 million years ago ma represented a major shift in the climate system and was characterized by a gradual cooling trend and the appearance of large continental ice sheets over northern eurasia and north america paleo evidence indicates that the ppt was accompanied and possibly caused by a decrease in atmospheric co2 but the temporal resolution of co2 reconstructions is low for this period of time and uncertainties remain large therefore instead of applying existent co2 reconstructions we solved an inverse problem by finding a schematic co2 concentration scenario that allows us to simulate the temporal evolution of key climate characteristics in agreement with paleoclimate records to this end we performed an ensemble of transient simulations with an earth system model of intermediate complexity from which we derived a best guess transient co2 scenario for the interval from 3 2 to 2 4 ma that gives the best fit between the simulated and reconstructed benthic 18o and global sea surface temperature evolution our data constrained co2 scenarios are consistent with recent co2 reconstructions and suggest a gradual co2 decline from 375 425 to 275 300 ppm between 3 2 and 2 4 ma in addition to a gradual decline the best fit to paleoclimate data requires the existence of pronounced co2 variability coherent with the 41 kyr 1 kyr 1000 years obliquity cycle in our simulations the long term co2 decline is accompanied by a relatively abrupt intensification of northern hemisphere glaciation at around 2 7 ma this is the result of a threshold behaviour of the ice sheets response to gradual co2 decrease and orbital forcing the simulated northern hemisphere ice sheets during the early pleistocene glacial cycles reach a maximum volume equivalent to a sea level drop of about 40 m both ice volume and benthic 18o are dominated by 41 kyr cyclicity our simulations suggest that before 2 7 ma greenland was ice free during summer insolation maxima and only partly ice covered during periods of minimum summer insolation a fully glaciated greenland comparable to its present day ice volume is modelled only during glacial maxima after 2 7 ma and more continuously after 2 5 ma

active tectonics along the cul de sac enriquillo plain and seismic hazard for port au prince haiti abstract the active faults in haiti were not well known and no detailed mapping of active fault traces was available before the 2010 m7 0 earthquake the lack of detailed fault mapping hindered the interpretation of the event and the seismic hazard assessment here using high resolution lidar topography aerial photographs bathymetric charts together with geological data complemented with field observations we carried out a morphotectonic analysis at a variety of scales we analyzed the drainage network at the northern front of the massif de la selle sierra de bahoruco msb by mapping the fans of the main rivers and their associated drainage basins we found that the areas of all the fans were compatible with the sizes of their drainage basins except the paleofan of port au prince we interpret that this paleofan has been offset by 7 9 0 3 km across the main strike slip enriquillo plantain garden fault epgf and we estimate a minimum horizontal slip rate of 3 mm yr over the pleistocene moreover in the cul de sac enriquillo plain within which the capital city of port au prince is located we mapped numerous nw se to wnw ese striking quaternary folds and thrust faults some of the thrust faults are north dipping and located to the southern front of the matheux neiba lower miocene fold other thrusts such as those near ganthier jacquet nan cadastre and port au prince are south dipping and located along the northern front of the msb lower miocene fold previously saint fleur et al 2015 showed that the 2010 haiti earthquake activated both one of the young thrusts lamentin and the epgf consistent with oblique convergence between the caribbean and the north american plates

pleistocene sea surface temperature evolution early cooling delayed glacial intensification and implications for the mid pleistocene climate transition the mid pleistocene climate transition mpt is defined by the emergence of high amplitude quasi 100 ka glacial interglacial cycles from a prior regime of more subtle 41 ka cycles this change in periodicity and amplitude cannot be explained by a change in external astronomical forcing here we review and integrate published records of sea surface temperatures ssts to assess whether a common global expression of the mpt in the surface ocean can be recognized and examine our findings in light of mechanisms proposed to explain climate system reorganization across the mpt we show that glacial interglacial variability in ssts is superimposed upon a longer term cooling trend in oceanographic systems spanning the low to high latitudes regional variability exists in the timing of the onset and magnitude of cooling but in most cases a long term cooling trend begins or intensifies from 1 2 ma marine isotope stage mis 35 34 the sst cooling accompanies a long term trend towards higher global ice volume as recorded in benthic foraminifera 18o but predates a step like increase in 18o at 0 9 ma mis 24 22 that is argued to reflect expansion of continental ice sheets the strongest expression of pleistocene cooling is found during glacial stages whereas minor or negligible trends in interglacial temperatures are identified however pronounced cooling during both glacial and interglacial maxima is evident at 0 9 ma alongside the long term sst cooling trends quasi 100 ka cycles begin to emerge in both the sst and 18o records at 1 2 ma and become dominant with the expansion of the ice sheets at 0 9 ma we show that the intensified glacial stage cooling is accompanied by evolving pco2 abyssal ocean ventilation atmospheric circulation and or dust inputs to the southern ocean these changes in diverse environmental parameters suggest that glacial climate boundary conditions evolved across the mpt in turn these modified boundary conditions may have altered climate sensitivity to orbital forcing by placing pre existing ice sheets closer to some threshold of climate ice sheet response

palaeoclimate warmth and glaciation the gradual expansion of northern hemisphere glaciation about 3 6 million years ago followed a period of prolonged warmth an analysis of ancient sea surface temperatures fuels the debate surrounding the roles of atmospheric carbon dioxide and global circulation in the cooling

global deepwater circulation between 2 4 and 1 7 ma and its connection to the onset of northern hemisphere glaciation we have generated an early pleistocene benthic isotopic record for the ocean drilling program odp site 807 2804 m from the western equatorial pacific between 2 4 and 1 7 ma the benthic 13c of this site and a few other deep pacific sites was consistently higher than the southern ocean site mv0502 4jc 4286 m pointing to a reversal relative to the current gradient and hence implying a different circulation regime we reconstructed the deep water mass distribution of this interval using a collection of benthic isotope records from 15 pacific and 10 atlantic sites and a 13c 18o mixing model a two end member mixing regime between the north atlantic deep water nadw and the antarctic bottom water aabw with properties very different from today was identified the southern ocean showed strong signs of stratification and aabw with low benthic 13c but high 18o values reached out to other basins only below 4000 m in contrast nadw ventilated most of the ocean interior contributing 70 to the pacific deep water pdw volumetrically our model results also reveal a strong remineralization effect at the bottom sites of the pacific and the atlantic suggesting significant accumulation of respired carbon in the bottom water between 2 4 and 1 7 ma we propose that such a circulation pattern was initiated by the reversal of salinity gradient between aabw and nadw from 3 0 to 2 4 ma possibly linked to antarctic sea ice expansion and reduced southward heat transport during the onset of northern hemisphere glaciation nhg

oceanographic and climatic evolution of the southeastern subtropical atlantic over the last 3 5 ma abstract the southeast atlantic ocean is dominated by two major oceanic systems the benguela upwelling system one of the world s most productive coastal upwelling cells and the agulhas leakage which is important for transferring warm salty water from the indian ocean to the atlantic ocean here we present a multi proxy record of marine sediments from odp site 1087 we reconstruct sea surface temperatures u 37 k and tex86 indices marine primary productivity total chlorin and alkenone mass accumulation rates and terrestrial inputs derived from southern africa ti al and ca ti via xrf scanning to understand the evolution of the southeast atlantic ocean since the late pliocene in the late pliocene and early pleistocene odp site 1087 was situated within the benguela upwelling system which was displaced southwards relative to present we recognize a series of events in the proxy records at 3 3 3 0 2 2 1 5 0 9 and 0 6 ma which are interpreted to reflect a combination of changes in the location of major global wind and oceanic systems and local variations in the strength and or position of the winds which influence nutrient availability although there is a temporary sst cooling observed around the initiation of northern hemisphere glaciation inhg proxy records from odp site 1087 show no clear climatic transition around 2 7 ma but instead most of the changes occur before this time this observation is significant because it has been previously suggested that there should be a change in the location and or strength of upwelling associated with this climate transition rather the main shifts at odp site 1087 occur at ca 0 9 ma and 0 6 ma associated with the early mid pleistocene transition empt with a clear loss of the previous upwelling dominated regime this observation raises the possibility that reorganisation of southeast atlantic ocean circulation towards modern conditions was tightly linked to the empt but not to earlier climate transitions

the relationship between environmental change and the extinction of the nannoplankton discoaster in the early pleistocene the long ranging nannoplankton genus discoaster went extinct in the early pleistocene one of the most significant events in the cenozoic nannofossil record the causal factors of this extinction are poorly constrained at least partially because the ecology of discoaster is not well understood we investigate the relationship between the extinction and environmental changes by comparing a suite of high resolution nannofossil assemblage data at four ocean drilling program sites to published environmental proxy records through the use of multivariate analysis we determine discoaster shared environmental preferences with the extant species florisphaera profunda which thrives in the lower photic zone near the nutricline in locations where the water column is stratified we show that the last occurrence of discoaster was globally diachronous rather than synchronous as previously thought and likely took place in the equatorial atlantic ocean we propose that the demise of discoaster was a two stage process a decrease in sea surface temperatures and increase in climate variability led to a global decline in discoaster abundance the extinction event itself correlates to shoaling of the nutricline as signified by a decrease in the carbon isotopic gradient between surface and thermocline foraminifera we hypothesize that the combination of global cooling and a shoaling of the nutricline greatly reduced discoaster s deepwater niche and contributed to its extinction this may suggest that ocean stratification and the depth of the nutricline are important contributors to overall nannoplankton diversity

initiation of northern hemisphere glaciation and strengthening of the northeast indian monsoon ocean drilling program site 758 eastern equatorial indian ocean the indian monsoon system as recorded by ocean floor biota benthic foraminifera at ocean drilling program site 758 in the eastern equatorial indian ocean has varied dramatically over the past 5 5 m y long after the onset of the monsoons at 10 8 ma benthic foraminifera that thrive with high productivity year round were common before the formation of northern hemisphere continental ice sheets ca 3 1 2 5 ma indicating that the summer southwest monsoon had high intensity and long seasonal duration ca 2 8 ma benthic faunas became dominated by taxa that flourish with a seasonally strongly fluctuating food supply indicating that the northeast winter monsoon during which primary productivity is relatively low increased in duration and strength to form a system similar to that of today the change occurred coeval with the initiation of the northern hemisphere glaciation documenting a close link between the development of the indian monsoon and northern hemisphere glaciation

growth of the maritime continent and its possible contribution to recurring ice ages the areal extent of the maritime continent the islands of indonesia and surrounding region has grown larger by 60 since 5 ma we argue that this growth might have altered global climate in two ways that would have contributed to making recurring ice ages possible first because rainfall over the islands of the maritime continent not only is heavier than that over the adjacent ocean but also correlates with the strength of the walker circulation the growth of the maritime continent since 5 ma may have contributed to the cooling of the eastern tropical pacific since that time scaling relationships between the strength of the walker circulation and rainfall over the islands of the maritime continent and between sea surface temperature sst of the eastern tropical pacific and the strength of easterly wind stress suggest that the increase in areal extent of islands would lead to a drop in that sst of 0 75 c although only a fraction of the 3 4 c decrease in ssts between the eastern and western tropical pacific the growth of the maritime continent may have strengthened the walker circulation increased the east west temperature gradient across the pacific and thereby enabled ice sheets to wax and wane over canada since 3 ma second because the weathering of basaltic rock under warm moist conditions extracts co2 from the atmosphere more rapidly than weathering of other rock or of basalt under cooler or drier conditions the increase in weathering due to increasing area of basalt in the maritime continent may have drawn down enough co2 from the atmosphere to affect global temperatures simple calculations suggest that increased weathering of basalt might have lowered global temperatures by 0 25 c possibly important for the overall cooling

the relationship between neogene dinoflagellate cysts and global climate dynamics abstract the neogene period 23 03 2 58 ma underwent a long term relatively gradual cooling trend culminating in the glacial interglacial climate of the quaternary palaeoclimate studies on the neogene have provided important information for understanding how modern patterns of atmospheric and oceanic circulation developed and how they may relate to wider environmental change here we use a newly created global database of neogene dinoflagellate cysts the tertiary oceanic parameters information system topis to investigate how dinoflagellate cysts recorded the cooling of neogene surface marine waters on a global scale species with warm and cold water preferences were determined from previously published literature and extracted from the database percentages of cold water species were calculated relative to the total number of species with known temperature preferences from each site and compared throughout the neogene at differing latitudes overall the percentage of cold water species increases gradually through the neogene this trend indicates a gradual global cooling that is comparable to that reported from other marine and terrestrial proxies this also demonstrates the use of dinoflagellate cysts in determining temperature change on both extended temporal and wide geographical scales the increase in the percentage of cold water species of dinoflagellate cysts recorded worldwide from the early and middle miocene to the late pliocene indicates a global scale forcing agent on neogene climate such as co2

linking desert evolution and coastal upwelling pliocene climate change in namibia a late pliocene high resolution pollen record from the southeast atlantic ocean drilling program site 1082 registers vegetation development in southwest africa the marine record is continuous ranges from 3 5 to 1 7 ma and has a millennial resolution between 2 9 and 1 9 ma changes in climate and vegetation correspond to the matuyama diatom maximum of the namibian upwelling system and seem to be highly susceptible to latitudinal shifts in the polar front zone of the southern ocean a northward advance of the polar fronts is connected with an increase in winter rainfall in southwest africa rapid desiccation in namibia at 2 2 ma is associated with increasing upwelling and decreasing sea surface temperatures along the coast

pliocene warmth polar amplification and stepped pleistocene cooling recorded in ne arctic russia understanding the evolution of arctic polar climate from the protracted warmth of the middle pliocene into the earliest glacial cycles in the northern hemisphere has been hindered by the lack of co

an early pleistocene atmospheric co2 record based on pedogenic carbonate from the chinese loess deposits abstract the tight coupling between temperature and atmospheric co2 is shown by ice core records for the past 0 8 million years myr however the modern atmospheric partial pressure of co2 pco2 has exceeded previous interglacial pco2 levels over the past 0 8 myr suggesting that the earlier part of the pleistocene and pliocene might be a better analog of today s radiative forcing of co2 the early pleistocene experienced a constant cooling characterized by the intensification of northern hemisphere glaciations existing pco2 records developed from marine organic matter and inorganic precipitates however disagree with the trends and absolute values of co2 over this time interval here we present quantitative interglacial pco2 estimates from 2 6 0 9 myr using the stable carbon isotopic compositions of pedogenic carbonates collected from the chinese loess plateau clp our pco2 records provide the first documentation of pco2 from continental sedimentary deposits over the early pleistocene the successive decrease of our pco2 records is broadly consistent with the increase in deep sea o 18 and the overall decline of sea surface temperature sst at this time but in contrast with the increasing peak interglacial pco2 recorded in ice cores for the last 0 8 myr

the carbonate chemistry of grand bahama bank waters after 18 years another look major features of the chemistry of northern grand bahama bank waters found in 1981 were similar to those found by broecker and takahashi in 1962 and 1963 measured variations in salinity and extent of caco3 removal are close to the same our findings indicate a more complex salinity distribution on the northern banks probably resulting from transport of high salinity waters from the south and higher pco2 values in the high salinity waters inorganic 14co2 measurements made in this study can be used to calculate very approximate residence times of water on the bank there is general agreement with the values previously determined by broecker and takahashi ship aerial and satellite observations indicate that whitings are not randomly distributed over the bank they form a halo around the northern and western flanks of the high salinity waters s greater than 40 the rate of caco3 removal is about 1 5 times faster in the waters where the whitings are common than in the high salinity waters even though our analytic precision was over 80 times greater than the change predicted in alkalinity if whitings precipitate directly from seawater no differences could be found between whiting and adjacent waters in our opinion the major features responsible for creating whitings controlling their distribution and determining caco3 removal rates on the grand bahama bank remain largely unresolved

upwelling intensification as part of the pliocene pleistocene climate transition a deep sea sediment core underlying the benguela upwelling system off southwest africa provides a continuous time series of sea surface temperature sst for the past 4 5 million years our results indicate that temperatures in the region have declined by about 10 c since 3 2 million years ago records of paleoproductivity suggest that this cooling was associated with an increase in wind driven upwelling tied to a shift from relatively stable global warmth during the mid pliocene to the high amplitude glacial interglacial cycles of the late quaternary these observations imply that atlantic ocean surface water circulation was radically different during the mid pliocene

a perpetually running enso in the pliocene abstract difficulties remain with theoretical explanations of the apparent reduced zonal sea surface temperature gradient in the tropical pacific of the pliocene one favored hypothesis is that it was a permanent el nino state with the warm phase of enso remaining fixed over millions of years here an alternative is suggested that there was a perpetually running enso with a shorter return time than is observed today and that the apparently reduced zonal gradient is an alias rectification of a high frequency signal governed by the growth patterns of the foraminifera used to provide proxy temperatures the hypothesis is probably testable in the modern ocean with comparatively modest measurements of foraminifera behavior in time

strong interannual variation of the indian summer monsoon in the late miocene the modern asian monsoon system exhibits strong interannual variation which has profound environmental and economical impacts it has been well documented that the mean asian monsoon state underwent significant changes in the late miocene 11 5 ma ago but how the interannual variability of the monsoon climate evolved during this period is still largely unknown in this study a long term simulation of the late miocene with a fully coupled atmosphere ocean general circulation model echam5 mpi om at t31l19 resolution is used to explore the interannual variation of the indian summer monsoon ism in the late miocene the regional climate model cosmo clm with a higher spatial resolution 1 1 is further employed to better characterize the spatial patterns of these variations our results show that although the mean ism circulation is weaker in the late miocene runs its interannual variation is as strong as or even stronger than at present and the dominant periods 2 6 2 7 years are shorter than at present 3 4 8 4 years it is noticed that while the extratropical influence on the ism variability is weaker than present a persistent el nino southern oscillation with stronger than present interannual variability is observed in our late miocene run this may have maintained a strong interannual variation of the ism with a shorter period in the late miocene our findings do not only improve our understanding of the asian monsoon evolution in the late miocene but also shed light on the future changes in the interannual variability of the ism

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

a 5 million year comparison of mg ca and alkenone paleothermometers geochemical sea surface temperature sst proxies such as the magnesium to calcium ratio mg ca in foraminifera and the alkenone unsaturation index uk 37 are becoming widely used in pre pleistocene climate records this study quantitatively compares previously published mg ca and uk 37 data from ocean drilling program odp site 847 in the eastern equatorial pacific to assess the utility of these proxies to reconstruct tropical sst over the last 5 ma foraminiferal mg ca sst calibrations that include a dissolution correction are most appropriate at this location because they provide sst estimates for the youngest sample that are close to modern mean annual sst the long term trends in the two records are remarkably similar and confirm a 3 5 c cooling trend from the early pliocene warm period to the late pleistocene noted in previous work absolute temperature estimates are similar for both proxies when errors in the dissolution correction used to estimate sst from mg ca are taken into account comparing the two sst records at odp site 847 to other records in the region shows that the eastern equatorial pacific was 2 4 c warmer during the early pliocene compared to today

why the south pacific convergence zone is diagonal during austral summer the majority of precipitation over the pacific ocean is concentrated in the south pacific convergence zone spcz the surface boundary conditions required to support the diagonally northwest southeast oriented spcz are determined through a series of experiments with an atmospheric general circulation model continental configuration and orography do not have a significant influence on spcz orientation and strength the key necessary boundary condition is the zonally asymmetric component of the sea surface temperature sst distribution this leads to a strong subtropical anticyclone over the southeast pacific that on its western flank transports warm moist air from the equator into the spcz region this moisture then intensifies diagonal bands of convection that are initiated by regions of ascent and reduced static stability ahead of the cyclonic vorticity in rossby waves that are refracted toward the westerly duct over the equatorial pacific the climatological spcz is comprised of the superposition of these diagonal bands of convection when the zonally asymmetric sst component is reduced or removed the subtropical anticyclone and its associated moisture source is weakened despite the presence of rossby waves significant moist convection is no longer triggered the spcz disappears the diagonal spcz is robust to large changes up to 6 c in absolute sst i e where the sst asymmetry is preserved extreme cooling change 6 c results in a weaker and more zonal spcz due to decreasing atmospheric temperature moisture content and convective available potential energy

african climate change and faunal evolution during the pliocene pleistocene abstract environmental theories of african faunal evolution state that important evolutionary changes during the pliocene pleistocene interval the last ca 5 3 million years were mediated by changes in african climate or shifts in climate variability marine sediment sequences demonstrate that subtropical african climate periodically oscillated between markedly wetter and drier conditions paced by earth orbital variations with evidence for step like 0 2 ma increases in african climate variability and aridity near 2 8 ma 1 7 ma and 1 0 ma coincident with the onset and intensification of high latitude glacial cycles analysis of the best dated and most complete african mammal fossil databases indicates african faunal assemblage and perhaps speciation changes during the pliocene pleistocene suggesting more varied and open habitats at 2 9 2 4 ma and after 1 8 ma these intervals correspond to key junctures in early hominid evolution including the emergence of our genus homo pliocene pleistocene shifts in african climate vegetation and faunal assemblages thus appear to be roughly contemporary although detailed comparisons are hampered by sampling gaps dating uncertainties and preservational biases in the fossil record further study of possible relations between african faunal and climatic change will benefit from the accelerating pace of important new fossil discoveries emerging molecular biomarker methods for reconstructing african paleovegetation changes tephra correlations between terrestrial and marine sequences as well as continuing collaborations between the paleoclimatic and paleoanthropological communities

engineering geology of loess and loess like deposits a commentary on the russian literature loess and loess like deposits were much studied in the soviet union and are currently under investigation in russia and surrounding countries there is a vast literature in russian which touches on all aspects of loess science and technology in particular the studies of the origin of collapsibility are almost totally in russian and of course studies on the various regions of russia and the countries of the former soviet union fsu appear in russian this review looks at the literature in russian and attempts to pick out key contributors major topics and works and to identify the critical regions and zones of investigation because so many regions of the fsu had people living on loess ground there is a vast literature on engineering geology and ground engineering topics and this tends to dominate all the literature on loess in russian following russian practice the fine grained deposits under consideration are divided into loess and loess like deposits three main topics are recognised across the whole spectrum of loess research formation and distribution of loess deposits stratigraphy cyclicity and palaeoclimatology and engineering topics in particular hydrocollapse and subsidence and we concentrate on the engineering geology topics an attempt is made based on the map of abelev and abelev abelev yu m abelev m yu 1968 fundamentals of design and construction on collapsible macroporous soils 2nd ed stroiizdat moscow 431 pp in russian of collapsing loess deposits to define seven loess regions within the geographical limits of the old ussr the seven regions are those where geotechnical problems might be expected

eocene equator to pole surface ocean temperatures a significant climate problem eocene surface ocean paleotemperature data which illustrate a reduced equator to pole temperature gradient cooler tropical sea surface temperatures and a relatively small global temperature warming 2 c present a significant climatic enigma if the reconstructions are correct such a temperature distribution can be achieved through greater poleward heat transport by the ocean however the mechanism for a greater oceanic role is uncertain in addition the results from climate models for conditions of a substantially greater poleward heat transport by the oceans indicate a weak atmospheric circulation and highly seasonal continental interior climates the weak atmospheric circulation is consistent with the record of continent derived eolian sediment recovered in deep sea cores however the eocene paleobotanical evidence from continental interiors indicates a very mild seasonality the lack of consistency between model results oceanic data and terrestrial data defines the nature of the problem of eocene climates the solution must involve reinterpretation of at least one major source of information