climate and environment of a pliocene warm world the pliocene epoch 5 33 2 58 million years ago ma was a generally warmer and wetter interval with atmospheric co2 concentrations at or slightly above modern levels this paper provides an overview of pliocene vegetation sea surface temperatures and climate modelling outcomes most prominent changes in pliocene biome distribution compared to today include a northwards shift of temperate and boreal vegetation zones in response to a warmer and wetter climate as well as an expansion of tropical savannas and forests at the expense of deserts faunal analysis techniques and modelling experiments using the hadley centre climate model identified significantly higher pliocene sea surface temperatures at mid and high latitudes of the northern hemisphere with cooling or unchanged sea surface temperatures at low latitudes global mean annual surface temperatures mat are estimated to have been 2 to 3 c higher during the piacenzian 3 6 2 58 ma than today with a reduced equator to pole gradient the marine realm during the pliocene was characterised by a reconfiguration of ocean gateways particularly the narrowing of the indonesian seaway and closure of the central american isthmus which produced essentially a modern pattern of ocean circulation in the southern ocean a warm early pliocene gave way to late piacenzian cooling proxy data indicate a reduced east to west sea surface temperature gradient in the tropical pacific during the pliocene warmth the pliocene is one of the most intensively studied geological intervals of the pre quaternary no other warm period in the geological past yields such a unique combination of near modern atmospheric co2 concentrations palaeogeography and palaeobiology however this paper also identifies data gaps and shortcomings in the reconstruction of pliocene environments using proxy data and climate models on which future research should focus

seasonal stratification shell flux and oxygen isotope dynamics of left coiling n pachyderma and t quinqueloba in the western subpolar north atlantic blooms this annual population overturning is marked by a 0 7 increase in d 18 o in both species the shell flux of n pachyderma peaks during the spring bloom and in late summer when stratification is close to its minimum and maximum respectively both export periods contribute about equally and account for 95 of the total annual flux shell fluxes of t quinqueloba show only a single broad pulse in summer thus following the seasonal stratification cycle the d 18 oo fn pachyderma reflects temperatures just below the base of the seasonal sml without offset from isotopic equilibrium the d 18 op attern oft quinqueloba shows a nearly identical amplitude and correlates highly with the d 18 oo fn pachyderma therefore t quinqueloba also reflects temperature near the base of the sml but with a positive offset from isotopic equilibrium these offsets contrast with observations elsewhere and suggest a variable offset from equilibrium calcification for both species in the irminger sea the species consistently show a contrast in their flux timings their flux weighted dd 18 o will thus dominantly be determined by seasonal temperature differences at the base of the sml rather than by differences in their depth habitat consequently their sedimentary dd 18 o may be used to infer the seasonal contrast in temperature at the base of the sml citation jonkers l g j a brummer f j c peeters h m van aken and m f de jong 2010 seasonal stratification shell flux and oxygen isotope dynamics of left coiling n pachyderma and t quinqueloba in the western subpolar north atlantic paleoceanography 25 pa2204 doi 10 1029 2009pa001849

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

strengthening of north american dust sources during the late pliocene 2 7 ma here we present orbitally resolved records of terrestrial higher plant leaf wax input to the north atlantic over the last 3 5 ma based on the accumulation of long chain n alkanes and n alkanl 1 ols at iodp site u1313 these lipids are a major component of dust even in remote ocean areas and have a predominantly aeolian origin in distal marine sediments our results demonstrate that around 2 7 million years ago ma coinciding with the intensification of the northern hemisphere glaciation nhg the aeolian input of terrestrial material to the north atlantic increased drastically since then during every glacial the aeolian input of higher plant material was up to 30 times higher than during interglacials the close correspondence between aeolian input to the north atlantic and other dust records indicates a globally uniform response of dust sources to quaternary climate variability although the amplitude of variation differs among areas we argue that the increased aeolian input at site u1313 during glacials is predominantly related to the episodic appearance of continental ice sheets in north america and the associated strengthening of glaciogenic dust sources evolutional spectral analyses of the n alkane records were therefore used to determine the dominant astronomical forcing in north american ice sheet advances these results demonstrate that during the early pleistocene north american ice sheet dynamics responded predominantly to variations in obliquity 41 ka which argues against previous suggestions of precession related variations in northern hemisphere ice sheets during the early pleistocene

late quaternary palynology in marine sediments a synthesis of the understanding of pollen distribution patterns in the nw african setting abstract after a review of the first steps in marine palynology we show that the understanding of the northwest african setting is crucial to evaluate the potential of marine palynological studies elsewhere we studied distribution patterns of pollen grains in recent marine sediments off nw africa and were able to clearly relate patterns to modern pollen source areas vegetation belts and operating transport systems wind belts and ocean currents in particular patterns of quercus artemisia chenopodiaceae amaranthaceae ephedra gramineae and wet forest trees are very indicative of the position of the vegetation belts on the adjacent continent aeolian pollen transport is carried out by the northeast trade winds and the african easterly jet aej in the rain forest belt transport of pollen and fern spores also occurs by rivers a detailed comparison between recent pollen rain samples from terrestrial and marine sites between 21 and 12 n showed that the latitudinal range of vegetation belts is clearly reflected in the pollen samples of both environments a migration of the southern border of the sahara is reflected by the changing ratio between chenopodiaceae amaranthaceae pollen from the desert and gramineae pollen from the savannah belt distribution patterns of pollen for 9000 and 18 000 14 c yr bp last glacial maximum time slices based on pollen records from eleven marine cores between portugal and the gulf of guinea show significant latitudinal migrations of vegetation belts but a stable position of the main wind trajectories the aej had a stable position around 21 n the belt with trade winds had a stable position from morocco southwards changing vigour of the trade winds is clearly reflected by the patterns of isopollen contours and by changes in pollen influx records

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

links between iron supply marine productivity sea surface temperature and co2 over the last 1 1 ma received 3 july 2008 revised 9 october 2008 accepted 27 october 2008 published 14 february 2009 1 paleoclimatic reconstructions have provided a unique data set to test the sensitivity of climate system to changes in atmospheric co2 concentrations however the mechanisms behind glacial interglacial g ig variations in atmospheric co2 concentrations observed in the antarctic ice cores are still not fully understood here we present a new multiproxy data set of sea surface temperatures sst dust and iron supply and marine export productivity from the marine sediment core ps2489 2 odp site 1090 located in the subantarctic atlantic that allow us to evaluate various hypotheses on the role of the southern ocean so in modulating atmospheric co2 concentrations back to 1 1 ma we show that antarctic atmospheric temperatures are closely linked to changes in so surface temperatures over the last 800 ka and use this to synchronize the timescales of our marine and the european project for ice coring in antarctica epica dome c edc records the close correlation observed between iron inputs and marine export production over the entire interval implies that the process of iron fertilization of marine biota has been a recurrent process operating in the subantarctic region over the g ig cycles of the last 1 1 ma however our data suggest that marine productivity can only explain a fraction of atmospheric co2 changes up to around 40 50 ppmv occurring at glacial maxima in each glacial stage in this sense the good correlation of our sst record to the edc temperature reconstruction suggests that the initial glacial co2 decrease as well as the change in the amplitude of the co2 cycles observed around 400 ka was most likely driven by physical processes possibly related to changes in antarctic sea ice extent surface water stratification and westerly winds position

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

a revised picture of the structure of the monsoon and land itcz over west africa this article presents an overview of the land itcz intertropical convergence zone over west africa based on analysis of ncar ncep reanalysis data the picture that emerges is much different than the classic one the most important feature is that the itcz is effectively independent of the system that produces most of the rainfall rainfall linked directly to this zone of surface convergence generally affects only the southern sahara and the northern most sahel and only in abnormally wet years in the region a second feature is that the rainbelt normally assumed to represent the itcz is instead produced by a large core of ascent lying between the african easterly jet and the tropical easterly jet this region corresponds to the southern track of african easterly waves which distribute the rainfall this finding underscores the need to distinguish between the itcz and the feature better termed the tropical rainbelt the latter is conventionally but improperly used in remote sensing studies to denote the surface itcz over west africa the new picture also suggests that the moisture available for convection is strongly coupled to the strength of the uplift which in turn is controlled by the characteristics of the african easterly jet and tropical easterly jet rather than by moisture convergence this new picture also includes a circulation feature not generally considered in most analyses of the region this feature a low level westerly jet termed the african westerly jet plays a significant role in interannual and multidecadal variability in the sahel region of west africa included are discussions of the how this new view relates to other aspects of west africa meteorology such as moisture sources rainfall production and forecasting desertification climate monitoring hurricanes and interannual variability the west african monsoon is also related to a new paradigm for examining the interannual variability of rainfall over west africa one that relates changes in annual rainfall to changes in either the intensity of the rainbelt or north south displacements of this feature the new view presented here is consistent with a plethora of research on the synoptic and dynamic aspects of the african easterly waves the disturbances that are linked to rainfall over west africa and spawn hurricanes over the atlantic and with our knowledge of the prevailing synoptic and dynamic features this article demonstrate a new aspect of the west africa monsoon a bimodal state with one mode linked to dry conditions in the sahel and the other linked to wet conditions the switch between modes appears to be linked to an inertial instability mechanism with the cross equatorial pressure gradient being a critical factor the biomodal state has been shown for the month of august only but this month contributes most of the interannual variability this new picture of the monsoon and interannual variability shown here appears to be relevant not only to interannual variability but also to the multidecadal variability evidenced in the region between the 1950s and 1980s

nw african hydrology and vegetation during the last glacial cycle reflected in plant wax specific hydrogen and carbon isotopes abstract we present a hydrologic reconstruction of the sahara sahel transition covering the complete last glacial cycle 130 ka based on a combination of plant wax specific hydrogen d and carbon isotopes 13c the d and 13c signatures of long chain n alkanes from odp site 659 off nw africa reveal a significant anti correlation complementary to published pollen data we infer that this plant wax signal reflects sensitive responses of the vegetation cover to precipitation changes in the sahel region as well as varying contributions from biomes north of the sahara c3 domain by north east trade winds netw during arid phases especially the northern parts of the sahel likely experienced crucial water stress which resulted in a pronounced contraction of the vegetation cover thus reducing the amount of c4 plant waxes from the region the increase in netw strength during dry periods further promoted a more pronounced c3 plant wax signal derived from the north african c3 plant domain during humid periods the c4 dominated sahelian environments spread northward into the saharan realm in association with lower netw inputs of c3 plant waxes arid humid cycles deduced from plant wax d are in accordance with concomitant changes in weathering intensity reflected in varying major element distributions environmental shifts are generally linked to periods with large fluctuations in northern hemisphere summer insolation during marine isotope stages 2 and 3 when insolation variability was low coupling of the hydrologic regime to alkenone based estimates of ne atlantic sea surface temperatures becomes apparent

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

abrupt onset and termination of the african humid period rapid climate responses to gradual insolation forcing a detailed ca 100 yr resolution and well dated 18 ams 14 c dates to 23 cal ka bp record of latest pleistocene holocene variations in terrigenous eolian sediment deposition at odp site 658c off cap blanc mauritania documents very abrupt large scale changes in subtropical north african climate the terrigenous record exhibits a well defined period of low influx between 14 8 and 5 5 cal ka bp associated with the african humid period when the sahara was nearly completely vegetated and supported numerous perennial lakes an arid interval corresponding to the younger dryas chronozone punctuates this humid period the african humid period has been attributed to a strengthening of the african monsoon due to gradual orbital increases in summer season insolation however the onset and termination of this humid period were very abrupt occurring within decades to centuries both transitions occurred when summer season insolation crossed a nearly identical threshold value which was 4 2 greater than present these abrupt climate responses to gradual insolation forcing require strongly non linear feedback processes and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non linear climate sensitivity the african monsoon climate system is thus a low latitude corollary to the bi stable behavior of high latitude deep ocean thermohaline circulation which is similarly capable of rapid and large amplitude climate transitions

numerical simulations of particle size distributions comparison with analytical solutions and kaolinite flocculation experiments abstract the population balance equation has been used to describe the evolution of particle populations caused by aggregation and breakup processes for several decades only recently has it been used to efficiently and directly predict the temporal variation of particle size distribution psd for cohesive sediments by using the quadrature method of moments qmom in this study an extension of that effort carries out additional validations that compare with analytical solutions for pure coagulation systems pure breakup systems and combined coagulation and breakup systems besides a laboratory experiment is conducted in a five liter mixing chamber to provide steady state psd of suspended kaolinite with a chamber averaged kaolinite concentration 0 52 g l and shear rate 45 s 1 the model results match reasonably well with both of those from analytical solutions and kaolinite flocculation experiment results sensitivities regarding the selecting of different model input parameters such as fractal dimensions primary particle sizes aggregation and breakage fitting parameters and fragmentation distribution functions are also checked the results further confirm the capability of qmom to predict psd using its quadrature nodes and the corresponding weights

glacial and interglacial wind regimes over the eastern subtropical atlantic and north west africa analysis of aeolo marine dust deposits in the subtropical eastern atlantic enables the strength of the major wind patterns during the late quaternary to be evaluated and gives an insight into the climate of north africa

late quaternary climate changes in central africa as inferred from terrigenous input to the niger fan time series of terrigenous source elements al k ti zr from core geob4901 8 recovered from the deep sea fan of the niger river record variations in riverine sediment discharge over the past 245 000 yr although the flux rates of all the elements depend on physical erosion which is mainly controlled by the extent of vegetation coverage in central africa element al ratios reflect conditions for chemical weathering in the river basin maximum sediment input to the ocean occurs during cold and arid periods when precipitation intensity and associated freshwater runoff are reduced high carbonate contents during the same periods indicate that the sediment supply has a positive effect on river induced marine productivity in general variations in the terrestrial signals contain a strong precessional component in tune with changes in low latitude solar radiation however the terrestrial signal lags the insolation signal by several thousand years k al ti al and zr al records reveal that african monsoonal precipitation depends on high latitude forcing we attribute the shift between insolation cycle and river discharge to the frequently reported nonlinear response of african climate to primary orbital configurations which may be caused by a complex interaction of the secondary control parameters such as surface albedo and or thermohaline circulation

bulk composition of northern african dust and its source sediments a compilation abstract this paper presents a review of bulk compositional data of northern african dust and its potential source sediments and includes elemental isotope and mineralogical data northern african dust represents about one half of the total global atmospheric mineral dust burden and its uplift transport and deposition have strong impacts on climate and various terrestrial and marine ecosystems the chemical data set shows that an average northern african dust exhibits comparable si fe and mn contents with respect to the average composition of the upper continental crust is slightly depleted in the alkali metals k and na and enriched in ti and p however the complete data set yields clear evidence that northern african dust and its source sediments are compositionally heterogeneous on a regional scale and that this heterogeneity can be used to differentiate between major potential source areas on the basis of so called source markers an evaluation of these compositional fingerprints shows that the following parameters and especially their combination are effective in the discrimination of the most active source areas in northern africa ratio of ca mg fe wt calcite or carbonate content palygorskite occurrence and abundance illite kaolinite ratio nd 0 value and 87sr 86sr ratio for example the data set corroborates previous ideas which assign carbonate illite and palygorskite rich mineral dusts to north west ern source regions because most of the above listed source markers do not change substantially during transport even far traveled dusts may be assigned to specific potential source areas in northern africa some limitations of the presented data set are also discussed our compilation reveals some substantial gaps in the knowledge of the composition of source sediments and mineral dusts from important potential source areas that should be filled in the future the here compiled data set can be used as a reference frame when incorporating the composition of source sediments e g mineralogy into global or regional dust transport models and can be compared with source analysis by remote sensing or back trajectory analysis however source apportionment studies supported by our data set will not only be useful for actual dust samples but will also be helpful for the understanding of paleo wind directions and hence paleo climatological conditions through the investigation of quaternary eolian sediments deposited in and around northern africa

vegetation succession and climate change across the plio pleistocene transition in eastern azerbaijan central eurasia 2 77 2 45 ma abstract the plio pleistocene transition marked a key moment in global climate history characterised by the onset of major glaciations in the northern hemisphere the palaeoenvironmental history of the plio pleistocene transition is not well known for the caspian sea region despite its importance for global climate dynamics here we present an independently 40ar 39ar dated high resolution terrestrial palynological record spanning the plio pleistocene boundary based on a lacustrine marine sedimentary sequence from eastern azerbaijan despite complex pollen transport pathways and the proximity of closely stacked mountain vegetation belts in the greater and lesser caucasus the record shows that regional vegetation responded to milankovitch forced glacial interglacial cycles tentatively correlated with global climatic records spanning mis g8 to 98 2 77 2 45 ma the persistence of mesophilous forests during glacial times indicates that some settings in the south caspian basin acted as glacial refugia and that vegetation response to glaciations was muted by increased moisture availability linked to caspian transgression the palynological record shows a relationship with global 18o stacks and specifically to the obliquity record we anticipate that precise correlation with the global climatostratigraphic timescale will allow better understanding of the nature and timing of important transgressive events in the caspian sea and their relevance on a global scale

environmental control of pollen grain distribution patterns in the gulf of guinea and offshore nw africa the areas of marine pollen deposition are related to the pollen source areas by aeolian and fluvial transport regimes whereas wind transport is much more important than river transport pollen distribution patterns ofpinus artemisia chenopodiaceae amaranthaceae and asteraceae tubuliflorae trace atmospheric transport by the northeast trades pollen transport by the african easterly jet is reflected in the pollen distribution patterns of chenopodiaceae amaranthaceae asteraceae tubuliflorae andmitracarpus grass pollen distribution registers the latitudinal extension of sahel savannas and dry open forests marine pollen distribution patterns of combretaceae melastomataceae alchornea andelaeis reflect the extension of wooded grasslands and transitional forests pollen from the guinean congolian zambezian forest and from the sudanian guinean vegetation zones mark the northernmost extension of the tropical rain forest rhizophora pollen in marine sediments traces the distribution of mangrove swamps only near the continent pollen ofrhizophora mitracarpus chenopodiaceae amaranthaceae and pollen from the sudanian and guinean vegetation zones are transported by the upwelling under current and the equatorial under current where those currents act as bottom currents the distribution of pollen in marine sediments reflecting the position of major climatic zones desert dry tropics humid tropics can be used in tracing climatic changes in the past

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

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

late pliocene changes in the north atlantic current article i nfo during the late pliocene global climate changed drastically as the northern hemisphere glaciation nhg intensified it remains poorly understood how the north atlantic current nac changed in strength and position during this time interval such changes may alter the amount of northward heat transport and therefore have a large impact on climate in the circum north atlantic region and the growth of northern hemisphere ice sheets using the alkenone biomarker we reconstructed orbitally resolved sea surface temperature sst and productivity records at integrated ocean drilling project iodp expedition 306 site u1313 during the late pliocene and early pleistocene 3 68 2 45 million years ago ma before 3 1 ma ssts in the mid latitude north atlantic were up to 6 c higher than the present and surface water productivity was low indicating that an intense nac transported warm nutrient poor surface waters northwards starting at 3 1 ma surface water characteristics changed drastically as the nhg intensified during glacial periods at the end of the late pliocene and beginning of the pleistocene ssts decreased and surface water productivity in the mid latitude north atlantic increased reflecting a weakened influence of the nac at our site at the same time the increase in surface productivity suggests that the arctic front af reached down into the mid latitudes we propose that during the intensification of the nhg the nac had an almost pure west to east flow direction in glacials and did not penetrate into the higher latitudes the diminished northward heat transport would have led to a cooling of the higher latitudes which may have encouraged the growth of large continental ice sheets in the northern hemisphere

high sea surface temperatures in tropical warm pools during the pliocene sea surface temperatures in the tropical oceans were thought to have remained stable during a period of warmth about five million years ago reconstructions of the sea surface temperature from the caribbean and pacific suggest that tropical temperatures have in fact changed in concert with global mean temperatures over the past five million years

atmospheric co2 decline during the pliocene intensification of northern hemisphere glaciations 1 several hypotheses have been put forward to explain the onset of intensive glaciations on greenland scandinavia and north america during the pliocene epoch between 3 6 and 2 7 million years ago ma a decrease in atmospheric co2 may have played a role during the onset of glaciations but other tectonic and oceanic events occurring at the same time may have played a part as well here we present detailed atmospheric co2 estimates from boron isotopes in planktic foraminifer shells spanning 4 6 2 0 ma maximal pliocene atmospheric co2 estimates gradually declined from values around 410 atm to early pleistocene values of 300 atm at 2 0 ma after the onset of large scale ice sheets in the northern hemisphere maximal pco2 estimates were still at 2 5 ma 90 atm higher than values characteristic of the early pleistocene interglacials by contrast pliocene minimal atmospheric co2 gradually decreased from 310 to 245 atm at 3 2 ma coinciding with the start of transient glaciations on greenland values characteristic of early pleistocene glacial atmospheric co2 of 200 atm were abruptly reached after 2 7 ma during the late pliocene transition this trend is consistent with the suggestion that ocean stratification and iron fertilization increased after 2 7 ma in the north pacific and southern ocean and may have led to increased glacial co2 storage in the oceanic abyss after 2 7 ma onward

depth dependency of the paleocene eocene carbon isotope excursion paired benthic and terrestrial biomarker records ocean drilling program leg 208 walvis ridge 1 the paleocene eocene thermal maximum petm coincided with a negative carbon isotope excursion cie in carbonate and organic matter in terrestrial and marine records consequently the petm global warming of 5 6 c has been attributed to the rapid emission of a large amount of isotopically light carbon into the ocean atmosphere system and the magnitude of the cie has been used to estimate the amount of carbon greenhouse gas emitted however there are large discrepancies between the magnitude of the cie in marine and in terrestrial material in different types of marine carbonate records bulk carbonate planktic and benthic foraminiferal carbonate and in marine carbonate records from different locations the marine carbonate record of the cie may be incomplete in most deep sea bathyal abyssal locations because of ocean acidification and widespread dissolution of seafloor carbonates we demonstrate that the cie in benthic foraminiferal stable isotope records is relatively abrupt and not as gradual as portrayed in bulk carbonate records along the walvis ridge depth transect se atlantic the benthic cie is about 1 5 at 3600 m paleodepth in contrast to about 3 5 at 1500 m paleodepth consistent with depth dependent truncation by carbonate dissolution strong covariance between the benthic record and the stable carbon isotope values of terrestrial n alkanes isolated from the same core i e site 1263 supports a relatively rapid excursion of at least 3 5 but no more than 5 0

north pacific seasonality and the glaciation of north america 2 7 million years ago in the context of gradual cenozoic cooling the timing of the onset of significant northern hemisphere glaciation 2 7 million years ago is consistent with milankovitch s orbital theory which posited that ice sheets grow when polar summertime insolation and temperature are low however the role of moisture supply in the initiation of large northern hemisphere ice sheets has remained unclear the subarctic pacific ocean represents a significant source of water vapour to boreal north america but it has been largely overlooked in efforts to explain northern hemisphere glaciation here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic pacific ocean indicating that 2 7 million years ago late summer sea surface temperatures in this ocean region rose in response to an increase in stratification at the same time winter sea surface temperatures cooled winter floating ice became more abundant and global climate descended into glacial conditions we suggest that the observed summer warming extended into the autumn providing water vapour to northern north america where it precipitated and accumulated as snow and thus allowed the initiation of northern hemisphere glaciation

north atlantic climate evolution through the plio pleistocene climate transitions during the plio pleistocene the earth witnessed the growth of large northern hemisphere ice sheets and profound changes in both north atlantic and global climate here we present a 3 2 myr long orbitally resolved alkenone sea surface temperature sst record from deep sea drilling project dsdp site 607 41 n 33 w water depth 3427 m in the north atlantic ocean we employ a multi proxy approach comparing these new observations with existing bottom water temperature bwt and stable isotope time series from the same site and sst time series from other sites shedding new light on plio pleistocene climate change north atlantic temperature records show a long term cooling with two major steps occurring during the late pliocene 3 1 to 2 4 ma and the mid pleistocene 1 5 to 0 8 ma closely timed with intervals of major change in northern hemisphere ice sheets existing evidence suggests that the late pliocene cooling may have been caused by a thresholded response to secular changes in atmospheric carbon dioxide co2 while an explanation for the mid pleistocene cooling may involve glacial interglacial changes in atmospheric co2 it seems to also require a change in the behavior of the ice sheets themselves north atlantic climate responses were closely phased with benthic oxygen isotope 18o changes during the 41 kyr world indicating a strong common northern hemisphere high latitude imprint on north atlantic climate signals after the mid pleistocene transition mpt north atlantic sst records and the site 607 benthic carbon isotope 13c record are more closely phased with 18o whereas bwt significantly leads 18o in the 100 kyr band suggesting a shift from a northern to a southern hemisphere influence on north atlantic bwt we propose that the expansion of the west antarctic ice sheet wais across the mpt increased the production and export of antarctic bottom water from the southern ocean and subsequently controlled its incursion into the north atlantic especially during glacial intervals it follows that the early 100 kyr response of bwt implies an early response of the wais relative to the northern hemisphere deglaciation thus in the 100 kyr world both northern hemisphere and southern hemisphere processes affect climate conditions in the north atlantic ocean

the avaatech xrf core scanner technical description and applications to ne atlantic sediments abstract x ray fluorescence xrf core scanning provides rapid high resolution down to 1 mm records of chemical composition on split sediment cores the measurements are non destructive and require very limited sample preparation the new avaatech xrf core scanner operational since 2002 covers the atomic mass range from al to u instrument parameters especially tube voltage can be adjusted to provide optimum settings for selected elements or sets thereof owing to the nature of the surface of split sediment cores particularly effects resulting from sample inhomogeneity and surface roughness results are semiquantitative yet provide reliable records of the relative variability in elemental composition downcore selected case studies from diverse sedimentary settings in the ne atlantic ocean illustrate a range of applications of xrf logging data these include preliminary stratigraphic interpretations glacial interglacial cycles provenance studies of the terrigenous sediment fraction lithological characterization early diagenetic processes and distinction between carbonate phases aragonite v calcite

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

calibration of xrf core scanners for quantitative geochemical logging of sediment cores theory and application abstract on line analysis of split sediment cores by xrf core scanners has become increasingly popular in the past decade because it allows nondestructive extraction of near continuous records of element intensities from sediment cores with a minimum of analytical effort a disadvantage of xrf core scanning relative to conventional geochemical analysis is the problematic conversion of core scanner output to element concentrations the main reason for this long standing problem is the poorly constrained measurement geometry attributable to inhomogeneity of the specimens e g variable water content and grain size distribution irregularities of the split core surface and in some setups spatial variations in thickness of an adhesive pore water film which forms directly below a protective foil covering the core surface we propose a log ratio calibration model for xrf core scanners derived from a combination of xrf spectrometry theory principles of compositional data analysis and empirical evidence the log ratio calibration model provides accurate and precise predictions of sediment composition element concentrations from xrf core scanner output with a limited number of parameters namely 2 d 1 where d equals the number of chemical elements whose concentrations are to be estimated the model can accommodate the inherent non linearity of the relation between relative intensities and concentrations which is apparent from the fact that it provides unbiased estimates an immediate corollary of our results is that log ratios of element intensities which are related to log ratios of element abundances by a simple linear transformation provide the most easily interpretable signals of relative changes in chemical composition consistent use of log ratios of element intensities or concentrations should minimise the risk of drawing erroneous conclusions from geochemical proxies the relative standard deviation precision of predicted element concentrations in core geob7920 is less than 2 stochastic simulations indicate that this level of precision can be attained with 40 randomly selected calibration specimens improved control over input errors and development of robust goodness of fit statistics allows xrf core scanning to be developed into a rigorous quantitative measurement technology the log ratio calibration equation derived in this study may be adapted to inter laboratory and inter instrument calibration as well

influences of high and low latitude processes on african terrestrial climate pleistocene eolian records from equatorial atlantic ocean drilling program site 663 high and low latitude forcing of terrestrial african paleoclimate variability is demonstrated using 900 ka eolian and biogenic component records from ocean drilling program site 663 in the eastern equatorial atlantic terrigenous eolian dust and phytolith savannah grass cuticle accumulation rate records vary predominantly at 100 and 41 kyr periodicities and spectral phase estimates implicate high latitude forcing the abundance of freshwater diatoms melosira transported from dry african lake beds varies coherently at 23 19 kyr orbital periodicities and at a phasing which implicates low latitude precessional monsoon forcing modeling studies demonstrate that african climate is sensitive to both high and low latitude boundary conditions african monsoon intensity is modulated by direct insolation variations due to orbital precession whereas remote high latitude forcing can be related to cool north atlantic sea surface temperatures ssts which promote african aridity and enhance dust transporting wind speeds the site 663 terrigenous and phytolith records covary with north atlantic sst variability at 41 n site 607 we suggest that pleistocene african climate has responded to both high latitude north atlantic sst variability as well as low latitude precessional monsoon forcing the high latitude influence dominates the sedimentary record prior to circa 2 4 ma terrigenous variations occurred primarily at precessional periodicities 23 19 kyr indicating that african climate was largely controlled by low latitude insolation variations prior to the onset of high amplitude glacial interglacial climate change

isopollen maps for 18 000 years b p of the atlantic offshore of northwest africa evidence for paleowind circulation distribution patterns of the most important pollen types from southern european and northwest african source areas for the 18 000 years b p time slice are reconstructed from pollen records of 14 well dated deep sea cores located between 37 and 9 n and compared with the modern pollen distribution in this area it is concluded that the belt with maximum african easterly jet transport did not shift latitudinally during the last glacial interglacial transition but remained at about 20 n furthermore it is substantiated that the trade winds did not shift latitudinally during the last glacial interglacial transition this evidence is not compatible with an atmospheric circulation model that assumes a zone of surface westerlies in the northern part of northwest africa trade winds during glacial episodes did however intensify especially from about 36 to 24 n

distribution of major elements in atlantic surface sediments 36 n 49 s imprint of terrigenous input and continental weathering 1 numerous studies use major element concentrations measured on continental margin sediments to reconstruct terrestrial climate variations the choice and interpretation of climate proxies however differ from site to site here we map the concentrations of major elements ca fe al si ti k in atlantic surface sediments 36 n 49 s to assess the factors influencing the geochemistry of atlantic hemipelagic sediments and the potential of elemental ratios to reconstruct different terrestrial climate regimes high concentrations of terrigenous elements and low ca concentrations along the african and south american margins reflect the dominance of terrigenous input in these regions single element concentrations and elemental ratios including ca e g fe ca are too sensitive to dilution effects enhanced biological productivity carbonate dissolution to allow reliable reconstructions of terrestrial climate other elemental ratios reflect the composition of terrigenous material and mirror the climatic conditions within the continental catchment areas the atlantic distribution of ti al supports its use as a proxy for eolian versus fluvial input in regions of dust deposition that are not affected by the input of mafic rock material the spatial distributions of al si and fe k reflect the relative input of intensively weathered material from humid regions versus slightly weathered particles from drier areas high biogenic opal input however influences the al si ratio fe k is sensitive to the input of mafic material and the topography of andean river drainage basins both ratios are suitable to reconstruct african and south american climatic zones characterized by different intensities of chemical weathering in well understood environmental settings

lack of a weathering signal with increased cenozoic erosion the late cenozoic has been marked by large and rapid fluctuations in temperature this cooling has been attributed to accelerated erosion with concomitant increased chemical weathering rates and co2 drawdown from the atmosphere at the same time much of the supporting evidence appears to be affected by a sampling bias implying that global erosion and weathering remained largely constant over the past millions of years we suggest that sedimentary archives of geomorphic activity such as grain size and the ratio of terrestrial to oceanic sedimentation which show accelerated erosion are not subject to these biases furthermore the active tectonic settings where these erosion increases were likely to have taken place are exactly those locations where chemical weathering signals are least likely to faithfully follow physical erosion rates a lack of evidence for an increase in chemical weathering does not necessarily preclude an increase in physical erosion in this contribution we suggest an alternative interpretation in which erosion rates have increased in the late cenozoic but without significantly increased silicate weathering which can explain the meagre response of chemical weathering proxies

high amplitude variations in north atlantic sea surface temperature during the early pliocene warm period 1 we provide the first continuous orbital resolution sea surface temperature sst record from the high latitude north atlantic a region critical to understanding the origin of the plio pleistocene ice ages and proximal to regions that became frequently glaciated after 2 7 ma we analyzed sediments from ocean drilling program site 982 over the last 4 ma for their alkenone unsaturation index and compared this surface water signal to a benthic 18o record obtained from the same section we find that while ocean surface temperatures were significantly warmer 6 c than modern temperatures during the early pliocene they were also as variable as those during the late pleistocene a surprising result in light of the subdued variance of oxygen isotopic time series during the interval of 3 5 ma we propose two possible explanations for the high orbital scale sst variability observed either that a strong high latitude feedback mechanism not involving large continental ice sheets alternately cooled and warmed a broad region of the northern high latitudes or that by virtue of its location near the northern margin of the north atlantic drift the site was unusually sensitive to obliquity driven climate shifts on supraorbital time scales a strong sustained cooling of north atlantic ssts 4 5 c occurred from 3 5 to 2 5 ma and was followed by an interval of more modest cooling an additional 1 5 c from 2 5 ma to the present evolutionary orbital scale phase relationships between north atlantic sst and benthic 18o show that sst began to lead 18o significantly coincident with the onset of strong cooling at site 982 3 5 ma we speculate that these changes were related to the growth and subsequent persistence of a greenland ice sheet of approximately modern size through interglacial states

coherent high and low latitude climate variability during the holocene warm period a faunal record of sea surface temperature sst variations off west africa documents a series of abrupt millennial scale cooling events which punctuated the holocene warm period these events evidently resulted from increased southward advection of cooler temperate or subpolar waters to this subtropical location or from enhanced regional upwelling the most recent of these events was the little ice age which occurred between 1300 to 1850 a d when subtropical ssts were reduced by 3 to 4 c these events were synchronous with holocene changes in subpolar north atlantic ssts documenting a strong in phase link between millennial scale variations in high and low latitude climate during the holocene

the deglacial history of the western tropical atlantic as inferred from high resolution stable isotope records off northeastern brazil abstract the western south atlantic boundary currents represent a sensitive system within the global thermohaline circulation thc we investigated the impact of deglacial thc changes on the western tropical atlantic studied in six high resolution sediment cores from the upper continental slope of brazil the stratigraphy of the cores is mainly based on 14c ams dating of monospecific foraminiferal samples changes in the upper layer tropical ocean during the deglaciation are inferred from stable oxygen isotope measurements on planktic and benthic foraminifera variations in the 18o residuals are assumed to be mainly temperature related during the oldest and younger dryas cooling periods two major deglacial thc disturbances are reported from north atlantic sediment cores concomitant to the repeated thc slowdown we observe an upper layer warming in the tropical ocean a reduced northward heat export from the tropical areas during these periods weak north brazil current is additionally reflected by low meridional gradients in the stable oxygen records this generally agrees with results from coupled ocean atmosphere models

pliocene environmental change in west africa and the onset of strong ne trade winds odp sites 659 and 658 abstract pliocene vegetation dynamics and climate variability in west africa have been investigated through pollen and xrf scanning records obtained from sediment cores of odp site 659 18 n 21 w the comparison between total pollen accumulation rates and ti ca ratios which is strongly correlated with the dust input at the site showed elevated aeolian transport of pollen during dusty periods comparison of the pollen records of odp site 659 and the nearby site 658 resulted in a robust reconstruction of west african vegetation change since the late pliocene between 3 6 and 3 0 ma the savannah in west africa differed in composition from its modern counterpart and was richer in asteraceae in particular of the tribus cichorieae between 3 24 and 3 20 ma a stable wet period is inferred from the fe k ratios which could stand for a narrower and better specified mid pliocene mid piacenzian warm time slice the northward extension of woodland and savannah albeit fluctuating was generally greater in the pliocene ne trade wind vigour increased intermittently around 2 7 and 2 6 ma and more or less permanently since 2 5 ma as inferred from increased pollen concentrations of trade wind indicators ephedra artemisia pinus our findings link the ne trade wind development with the intensification of the northern hemisphere glaciations inhg prior to the inhg little or no systematic relation could be found between sea surface temperatures of the north atlantic with aridity and dust in west africa

the seasonal evolution of the atmospheric circulation over west africa and equatorial africa abstract this paper examines the mean annual cycle of rainfall and general circulation features over west africa and central africa for 1958 97 rainfall is examined using a 1400 station archive compiled by the first author other circulation features are examined using the ncep ncar reanalysis dataset important features of the reanalysis zonal wind field are shown to compare well with the seasonal evolution described by the radiosonde observations in addition to the well known african easterly jet aej of the northern hemisphere the seasonal evolution of its southern hemisphere counterpart is also described thermal wind calculations show that although the southern jet is weaker its existence is also due to a local reversal of the surface temperature gradient in the upper troposphere a strong semiannual cycle is shown in the 200 mb easterlies and a feature like the tropical easterly jet tej is evident south of the equator in january and february the paper describes the movement of the rainbelt

modern and last glacial maximum eolian sedimentation patterns in the atlantic ocean interpreted from sediment iron oxide content eolian dust derived from the desert regions of north africa is blown far into the tropical atlantic ocean by persistent easterly and northeasterly winds in this paper we demonstrate that the iron oxides hematite and goethite are a worthwhile addition to proxy monitors of eolian sedimentation in the tropical atlantic iron oxides are identified by diffuse reflectance spectrophotometry a technique capable of identifying these minerals in concentrations as low as 0 01 by weight we analyze samples from both the modern and last glacial maximum lgm synoptic levels from 178 sample locations yielding a total of 356 samples distributed throughout the atlantic ocean to determine the relative contribution of the iron oxides we factor analyzed the modern and lgm levels as a single data set the iron oxide factor explains about 25 of the variance in the combined core top and lgm data set mapped factor scores for the lgm and modern ocean indicate high iron oxide values are present in just two regions one off eastern north america and the other off northwest africa in the region off eastern north america iron oxide occurs primarily during the lgm as the previously noted brick red lutite a unique sediment type derived from the erosion of permo carboniferous red beds in atlantic canada a larger lobe shaped area of iron oxide rich sediment is present off northwest africa in both the modern and lgm levels the modern iron oxide lobe is coincident with the distribution of eolian dust as determined by observations from ships satellites and analysis of air samples during the lgm iron oxides exhibit a similar distribution except the southern margin of the region shifts equatorward and iron oxide concentration increases

cortex a shipboard xrf scanner for element analyses in split sediment cores abstract the cortex corescanner texel is a non destructive xrf system for the logging of split sediment cores it is a seaworthy instrument that remains active during heavy weather conditions the scanner produces reliable counts for k to sr highly correlated with concentrations measured with atomic absorption spectrometry aas the option to scan al si and elements heavier than sr is in preparation a core section of 1 m can be scanned at 2 cm intervals within an hour a maximum resolution of 1 mm can be achieved at present each region and sedimentary environment requires separate calibration in the nearby future the generator settings will be standardized which may result in the development of a standard calibration procedure because of the high resolution of its semi quantitative records the cortex is a useful tool for detailed time series analysis inter core correlation and shipboard analysis

the mid pleistocene transition in the subtropical southwest pacific 1 reconstructions of subtropical southwest pacific climate variability over the pleistocene were derived from coupled planktic foraminiferal 18o mg ca measurements taken from a southern coral sea sediment core a clear shift from 40 kyr to 100 kyr modes of reconstructed glacial interglacial sea surface temperature sst variability is seen over the mid pleistocene transition and these fluctuations are shown to have remained coherent with the orbital obliquity cycle across the transition the likely origin of this strong obliquity signal in subtropical southwest pacific sst is shown to be the southern high latitudes and comparison with existing sst reconstructions from the equatorial pacific is consistent with the communication of the signal occurring principally by greenhouse gas forcing in contrast to the sst reconstruction regional hydrological cycle variability based on the calculated local component of 18osw change does not show significant coherence with obliquity after 1000 ka the decoupling of the sst and hydrological cycle responses over the mid pleistocene transition allows constraints to be placed on the evolution and extent of orbitally paced fluctuations within the coupled low latitude ocean atmosphere system

palynological evidence for a southward shift of the north atlantic current at 2 6 ma during the intensification of late cenozoic northern hemisphere glaciation the position of the north atlantic current nac during the intensification of northern hemisphere glaciation inhg has been evaluated using dinoflagellate cyst assemblages and foraminiferal geochemistry from a 260 kyr interval straddling the base of the quaternary system from two sites eastern north atlantic deep sea drilling project site 610 in the path of the present nac and central north atlantic integrated ocean drilling program site u1313 in the subtropical gyre stable isotope and foraminiferal mg ca analyses confirm cooling near the marine isotope stage mis g7 g6 transition 2 74 ma however a continued dominance of the dinoflagellate cyst operculodinium centrocarpum sensu wall and dale 1966 indicates an active nac in the eastern north atlantic for a further 140 kyr at mis 104 2 60 ma a profound dinoflagellate cyst assemblage turnover indicates nac shutdown in the eastern north atlantic implying elevated atmospheric pressure over the arctic and a resulting shift in the westerlies that would have driven the nac these findings challenge recent suggestions that there was no significant southward shift of the nac or the arctic front during inhg and reveal a fundamental climatic reorganization near the base of the quaternary

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

early pliocene increase in thermohaline overturning a precondition for the development of the modern equatorial pacific cold tongue unraveling the processes responsible for earth s climate transition from an el nino like state during the warm early pliocene into a modern like la nina dominated state currently challenges the scientific community recently the pliocene climate switch has been linked to oceanic thermocline shoaling at 3 million years ago along with earth s final transition into a bipolar icehouse world here we present pliocene proxy data and climate model results which suggest an earlier timing of the pliocene climate switch and a different chain of forcing mechanisms we show that the increase in north atlantic meridional overturning circulation between 4 8 and 4 0 million years ago initiated by the progressive closure of the central american seaway triggered overall shoaling of the tropical thermocline this preconditioned the turnaround from a warm eastern equatorial pacific to the modern equatorial cold tongue state about 1 million years earlier than previously assumed since 3 6 3 5 million years ago the intensification of northern hemisphere glaciation resulted in a strengthening of the trade winds thereby amplifying upwelling and biogenic productivity at low latitudes

intensification of the walker and hadley atmospheric circulations during the pliocene pleistocene climate transition when comparing new sea surface temperature sst records between the western and eastern equatorial pacific spanning the last 3 2 ma we found that the zonal temperature gradient over the entire tropical pacific irreversibly increased by 3 to 4 degrees c from 2 2 to 2 0 ma here we suggest a pronounced increase in atmospheric circulation from a weak to a strong zonal walker circulation wc during the early pleistocene evidence from other oceanic areas also suggests a strengthening in the meridional hadley circulation hc during the same time period therefore we also suggest that the invigoration of both atmospheric circulation patterns was intimately coupled during the plio pleistocene transition and likely linked to a shrinkage in the zonal extension of the tropical to subtropical warm sphere associated with a prominent increase in the pole to equator temperature gradient our conclusion refutes assumptions that the intensification of atmospheric circulation in the tropics and subtropics significantly contributed to the initiation of continental ice sheet formation at high latitudes since the onset of extensive northern hemisphere glaciation nhg occurred similar to 2 75 ma ago in the late pliocene instead the development of a stronger atmospheric circulation similar to 2 2 2 0 ma ago could have significantly contributed to the plio pleistocene climate cooling c 2010 elsevier b v all rights reserved

tropical ocean temperatures over the past 3 5 million years determining the timing and amplitude of tropical sea surface temperature sst change is an important part of solving the puzzle of the plio pleistocene ice ages alkenone based tropical sst records from the major ocean basins show coherent glacial interglacial temperature changes of 1 to 3 c that align with but slightly lead global changes in ice volume and deep ocean temperature over the past 3 5 million years tropical temperatures became tightly coupled with benthic 18o and orbital forcing after 2 7 million years we interpret the similarity of tropical sst changes in dynamically dissimilar regions to reflect top down forcing through the atmosphere the inception of a strong carbon dioxide greenhouse gas feedback and amplification of orbital forcing at 2 7 million years ago connected the fate of northern hemisphere ice sheets with global ocean temperatures since that time

sahel megadroughts triggered by glacial slowdowns of atlantic meridional overturning 1 the influence of the large scale ocean circulation on sahel rainfall is elusive because of the shortness of the observational record we reconstructed the history of eolian and fluvial sedimentation on the continental slope off senegal during the past 57 000 years our data show that abrupt onsets of arid conditions in the west african sahel were linked to cold north atlantic sea surface temperatures during times of reduced meridional overturning circulation associated with heinrich stadials climate modeling suggests that this drying is induced by a southward shift of the west african monsoon trough in conjunction with an intensification and southward expansion of the midtropospheric african easterly jet

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

astronomically modulated neogene sediment records from the south china sea 1 general global cooling over the neogene has been modulated by changes in earth s orbital parameters investigations of deep sea sediment sequences show that various orbital cycles can dominate climate records for different latitudes or for different time intervals however a comprehensive understanding of astronomical imprints over the entire neogene has been elusive because of the general absence of long continuous records extending beyond the pliocene we present benthic foraminiferal 18o and 13c records over the past 23 ma at ocean drilling program site 1148 in the northern south china sea and construct an astronomically tuned timescale tj08 for these records based on natural gamma radiation and color reflectance data at this site our results show that a 41 ka cycle has dominated sediment records at this location over the neogene displaying a linear response to orbital forcing a 100 ka cycle has also been significant however it is correlated nonlinearly with earth s orbital variations at the 100 ka band the sediment records also display a prominent 405 ka cycle although this cycle was coherent with orbital forcing during the oligocene and the early miocene it was not coherent with earth s orbital variations at the 405 ka band over the whole neogene amplification of northern hemisphere and southern hemisphere glaciation since the middle miocene may be responsible for this change in sedimentary response our benthic foraminifera 18o and 13c records further exhibit amplitude variations with longer periods of 600 1000 1200 and 2400 ka apparently these cycles are nonlinear responses to insolation forcing