monsoon related variations in zaire congo sediment load and influence of fluvial silicate supply on marine productivity in the east equatorial atlantic during the last 200 000 years two sediment cores from the zaire fan and the angola margin have been investigated for their composition of terrigenous and biogenic constituents respectively for the late quaternary kaolinite feldspar ratios and variations of terrigenous element ratios of zr ti k rb and al reveal that the composition of zaire river sediment load has fluctuated in tune with precessional variations of boreal summer insolation in particular the correspondence of high kaolinite feldspar and al k ratios with low latitude insolation maxima strongly corroborates the assumption that west african monsoonal precipitation and chemical weathering was enhanced during periods of increased central african heating the most striking feauture observed is that opal accumulation has been 2 to 10 times higher in zaire fan sediments than outside in continental margin sediments off angola although biogenic ba and corg fluctuations from both areas indicate that changes of total paleoproductivity were of the same magnitude in the zaire river plume and off angola from this we infer that the contribution of biogenic opal production to total paleoproductivity has been significantly higher within the zaire river plume than in the oceanic upwelling regime farther to the south off angola over the last 200 000 years the pattern of opal accumulation rates with respect to that of marine organic carbon implies that enhanced opal production off the zaire river to a great extent was the result of additional fluvial supply of dissolved silica during humid climates characterized by more intense chemical weathering on the continent while total paleoproductivity created by oceanic upwelling was high in periods of increased zonal trade wind intensity at precessional insolation minima and during cold more arid glacial climate conditions we presume that paleoproductivity off the zaire was controlled by the following two sources of nutrients 1 marine nutrients including nitrate and phosphate as well as the uptake of ba on particulate corg caused by upwelling and 2 silica mainly delivered by the zaire river dissolved silicate hence our results underline the importance of dissolved silicate in large rivers for marine silicate cycling in the tropical to subtropical atlantic at a millenial timescale

alkenone and coccolith records of the mid pleistocene in the south east atlantic implications for the u37k index and south african climate abstract successful application of the alkenone palaeothermometer the u 37 k index relies upon the assumption that fossil alkenone synthesisers responded to growth temperature changes in a similar manner to the modern producers chiefly the coccolithophores emiliania huxleyi and gephyrocapsa oceanica we compare coccolith and u 37 k data from odp site 1087 in the south east atlantic between 1500 and 500 ka and show that evolutionary events and changes in species dominance within the coccolithophore populations had little impact on the u 37 k record the relative abundances of the c37 and c38 alkenones also closely resembled those found in modern populations and suggest a similar temperature sensitivity of u 37 k during the early and mid pleistocene to that found at present these results support the application of the u 37 k index to reconstruct sea surface temperatures ssts throughout the quaternary the u 37 k record at odp site 1087 contains an sst signal that documents the emergence of the 100 kyr cycles that characterise the late quaternary ice volume records this is preceded by significant cooling at odp site 1087 marked by a negative shift in ssts and a positive shift in the planktonic 18o some 250 kyr earlier at ca 1150 1000 ka this results in a permanent fall in average ssts of around 1 5 c the predicted increase in aridity onshore as a result of this cooling can be identified in a number of published records from southern africa and may have played a role in some important evolutionary events of the mid pleistocene

ni speciation in a new caledonian lateritic regolith a quantitative x ray absorption spectroscopy investigation abstract changes in ni speciation in a 64 m vertical profile of a new caledonian saprolitic lateritic regolith developed over ultramafic rocks under tropical weathering conditions were investigated by exafs spectroscopy quantitative analysis of the exafs spectra by linear combination least squares fitting lc lsf using a large set of model compound spectra showed that ni hosted in primary silicate minerals olivine and serpentine in the bedrock is incorporated in secondary phyllosilicates serpentine and fe oxides goethite in the saprolite unit and mainly in goethite in the laterite unit a significant concentration of ni up to 30 of total ni is also hosted by mn oxides in the transition laterite i e the lowest part of the laterite unit which contains large amounts of mn oxides however the amount of ni associated with mn oxides does not exceed 20 of the total ni in the overlying laterite unit this sequence of ni species from bedrock to laterite yields information about the behavior of ni during tropical weathering of ultramafic rocks the different ni distributions in phyllosilicates in the bedrock randomly distributed and in the saprolite unit clustered indicate two generations of ni bearing phyllosilicates the first which formed at higher temperature is related to serpentinization of oceanic crust whereas the second one which formed at lower temperature is associated with post obduction weathering of ultramafic rocks in addition the observed decrease in the proportion of ni hosted by mn oxides from the transition laterite to the upper lateritic horizons indicates dissolution of mn oxides during the last stages of differentiation of the lateritic regolith i e lateritization finally the ubiquitous occurrence of ni bearing goethite emphasizes the major role of this phase in ni speciation at the different weathering stages and suggests that goethite represents the major host for ni in the final tropical weathering stages of new caledonian ultramafic rocks

vegetation change in equatorial west africa time slices for the last 150 ka abstract drawing on marine and terrestrial palynological data vegetation maps of equatorial west africa are presented for eleven time slices over the last 150 000 years long marine records are used as a basis for the regional picture and provide a chronology for the last glacial cycle much shorter terrestrial records help fill in the picture for the most recent periods and facilitate interpretation of regional patterns for the longer timescale temporal and spatial variation is revealed in relation to global patterns of climate change rain forest was widespread during oxygen isotope stages 1 and 5 but strongly reduced during stages 3 and 4 and especially during stages 2 and 6 when open grass rich vegetation prevailed glacial rain forest refuges are found in the southwest of the guinean mountains and along the eastern coast of the gulf of guinea miombo woodland of the zambezian vegetation zone expanded during stage 5 especially during the first half podocarpus forest had its largest expansion during substages 5d 115 to 105 ka and 5b 95 to 85 ka the last occurrence of podocarpus in the guinean mountains is during stage 5a the distribution of mangrove swamps was extremely reduced during glacial times during stage 6 savanna and open dry forest covered large areas along the northern coast of the gulf of guinea the southern saharan desert reached far to the south and the namib desert far to the north the area of rain forest was restricted mangrove swamps were strongly reduced and the area of podocarpus forest fluctuated during stage 5 large changes in the area of afromontane forest rain forest dry open forest and savanna occurred rain forest was widespread and mangroves were extensive along the coast during the last interglacial substage 5e podocarpus forest area strongly extended during substages 5d and 5b in substages 5c and 5a rain forest reclaimed areas it had lost in the previous substages 5d and 5b respectively mangrove swamps were less widespread in the later substages of stage 5 than during substage 5e during stage 4 the rain forest area was again strongly reduced and recovered only slightly during the following stage 3 also the mangrove swamp area was reduced except along the ivory coast and along the northwestern coast of the gulf of guinea podocarpus forest only occurred in angola and may be in congo during stage 4 again forest was much reduced during stage 2 and open vegetation types covered large parts of equatorial west africa mangrove swamps must have been rare at the beginning of the holocene mangrove swamps had recovered and reached their largest extension also the rain forests area increased in the early holocene and guinean and congolian rain forests were probably not separated by a savanna corridor now existing in togo and benin

a 30 000 yr record of land ocean interaction in the eastern gulf of guinea abstract a 30 000 yr dinocyst and pollen record from the eastern equatorial atlantic off cameroon has been investigated in order to identify land ocean linkages during the last deglacial transition a strong correlation between the abundance of brigantedinium spp and the ca fe ratio during the last glacial period suggests enhanced marine productivity in association with cool seawater temperatures and nutrient input linked to coastal upwelling and or a proximal river mouth dry conditions are recorded on the adjacent continent with a significant representation of open vegetation indicators and the afromontane taxon podocarpus after 17 cal ka bp these indicators register a sharp decline as a result of a climatic transition from the dry cooler conditions of the last glacial period to the wetter warmer conditions of the deglaciation simultaneously dinocysts show a significant shift from dominant heterotrophs to an increasing abundance of autotrophs reflecting warmer conditions significant changes are observed during the younger dryas with a return to drier conditions and higher salinities the start of the holocene is marked by very low salinity conditions reflecting optimal monsoonal conditions over west equatorial africa the end of the african humid period is observed between 6 and 5 cal ka bp followed by significant fluctuations in both terrestrial and oceanic proxies

ice age terrestrial carbon changes revisited n shackleton 1977 first proposed that changes in the marine 13 c record 13 c could be used to infer ice age changes in carbon storage on land the previously published best estimate from the marine record is equivalent to about 490 gt 0 32 13 c however adams et al 1990 utilized a pollen database to estimate a 1350 gt change in carbon storage which would cause a 13 c of about 0 90 the nearly trillion ton difference in estimates amounts to almost half of the total carbon stored on land to address the nature of this discrepancy i have reexamined the terrestrial carbon record based on a new pollen database compiled by r webb and the cooperative holocene mapping project cohmap group i estimate about 750 1050 gt glacial interglacial change in terrestrial carbon storage with the range reflecting uncertainties in carbon storage values for different biomes additional uncertainties apply to rainforest and wetland extent and presence of c4 plants which have a significantly different isotopic signature than c3 plants although some scenarios overlap a new estimate of carbon storage based on the oceanic 13 c record revised to 0 40 and 610 gt most estimates seem to fall outside the envelope of uncertainty in the marine record several possible explanations for this gap involve 1 a missing sink may be involved in land sea carbon exchange e g continental slopes 2 the geochemistry of the exchange process is not understood 3 carbon storage by biome may have changed under ice age boundary conditions or 4 the standard interpretation of whole ocean changes in the marine 13 c record requires reevaluation this latter conclusion receives some support from comparison of the 13 c records for 18 o stages 2 and 6 for the stage 6 glacial the 13 c changes are 50 60 larger than for the stage 2 glacial yet implications of increased aridity are not supported by longterm trends in atmospheric dust loading to summarize the above analysis implies that despite the uncertainties remaining in estimates of terrestrial carbon storage changes a case can be made that our understanding of the transfer process is incomplete and that the eventual explanation may require clarification of factors affecting the marine 13 c record

high resolution last deglaciation record from the congo fan reveals significance of mangrove pollen and biomarkers as indicators of shelf transgression abstract high abundances of mangrove pollen have been associated with transgressive cycles on tropical margins but the detailed relations between systems tracts and the taphonomy of the pollen are unclear we report here the occurrence and high abundance of rhizophora pollen in association with taraxerol a rhizophora sourced biomarker from a high resolution congo fan core covering the last deglaciation an age model based on 14c dates enables the temporal changes in taraxerol content and the percentage frequencies and flux pollen grains pg cm 2 103 yr 1 of mangrove pollen to be compared quantitatively with the lateral rate of transgression across the flooding surface derived from glacio hydro isostatic model output and the bathymetry of the margin rhizophora pollen concentrations and taraxerol content of the sediment are very strongly positively correlated with the lateral rate of transgression and indicate independently of any sequence stratigraphic context that mangrove pollen spikes are associated with the transgressive systems tract rather than the highstand systems tract or maximum flooding surface lower resolution longer term records from this margin indicate an association between taraxerol concentrations and transgressive rather than regressive phases the flux of these materials to the congo fan is interpreted as a function of the erosion of flooded mangrove swamp on the shelf and less importantly changing extent of mangrove habitat during sea level rise congo river palaeoflood events also result in reworking of mangrove pollen and supply to the fan but this mechanism is subdominant rhizophora pollen has been underestimated in many palynological studies undertaken on cores from the african margin because of inappropriate sieve mesh size used during laboratory preparation

mid pleistocene environmental change in tropical africa began as early as 1 05 ma palynological records from the congo fan reveal environmental change in equatorial africa occurring 1 05 ma ago 100 k y before the mid pleistocene climatic shift at 0 9 ma prior to 1 05 ma a glacial interglacial rhythm is not obvious in the african vegetation variation afterwards podocarpus spread in the mountains of central africa mainly during glacials and congo river discharge decreased the sequence of vegetation variation associated with the mid pleistocene glacials and interglacials differed from that observed during the late pleistocene between 0 9 and 0 6 ma interglacials were characterized by warm dry conditions and glacials were characterized by cool humid conditions while during the past 0 2 ma glacials were cold and dry and interglacials warm and humid our data indicate that before the northern hemisphere ice caps dramatically increased in size 0 9 0 6 ma low latitude climate forcing and response in the tropics played an important role in the initiation of 100 k y ice age cycles during the mid to late pleistocene however the climate conditions in the tropics were increasingly influenced by the glacialinterglacial variations of continental ice sheets

glacial interglacial changes in southern africa compound specific δ13c land plant biomarker and pollen records from southeast atlantic continental margin sediments this is part 2 of a study examining southwest african continental margin sediments from nine sites on a north south transect from the congo fan 4 s to the cape basin 30 s representing two glacial mis 2 and 6a and two interglacial stages mis 1 and 5e contents distribution patterns and molecular stable carbon isotope signatures of long chain n alkanes c27 c33 and n alkanols c22 c32 as indicators of land plant vegetation of different biosynthetic types were correlated with concentrations and distributions of pollen taxa in sediments of the same time horizons selected single pollen type data reveal details of vegetation changes but the overall picture is best illustrated by summing pollen known to predominantly derive from c4 plants or c4 plus cam plants the c4 plant signals in the biomarkers are recorded in the 13c data and in the abundances of c31 and c33n alkanes and the c32n alkanol calculated clusters of wind trajectories for austral summer and winter situations for the holocene and the last glacial maximum afford information on the source areas for the lipids and pollen and their transport pathways to the ocean this multidisciplinary approach provides clear evidence of latitudinal differences in leaf wax lipid and pollen composition with the holocene sedimentary data paralleling the current major phytogeographic zonations the northern sites congo fan area and northern angola basin get most of their terrestrial material from the congo basin and the angolan highlands dominated by c3 plants airborne particulates derived from the western and central south african hinterland dominated by deserts semideserts and savannah regions are rich in organic matter from c4 plants as can be expected from the present and glacial positions of the phytogeographic zones the carbon isotopic signatures of n alkanes and n alkanols both become isotopically more enriched in 13c from north to south in the northern part of the transect the relative importance of c4 plant indicators is higher during the glacials than in the interglacials indicating a northward extension of arid zones favoring grass vegetation in the south where grass rich vegetation merges into semidesert and desert the difference in c4 plant indicators is small

a north to south transect of holocene southeast atlantic continental margin sediments relationship between aerosol transport and compound specific δ13c land plant biomarker and pollen records 1 we examined near surface late holocene deep sea sediments at nine sites on a north south transect from the congo fan 4 s to the cape basin 30 s along the southwest african continental margin contents distribution patterns and molecular stable carbon isotope signatures of long chain n alkanes c27 c33 and n alkanols c22 c32 are indicators of land plant vegetation of different biosynthetic types which can be correlated with concentrations and distributions of pollen taxa in the same sediments calculated clusters of wind trajectories and satellite aerosol index imagery afford information on the source areas for the lipids and pollen on land and their transport pathways to the ocean sites this multidisciplinary approach on an almost continental scale provides clear evidence of latitudinal differences in lipid and pollen composition paralleling the major phytogeographic zonations on the adjacent continent dust and smoke aerosols are mainly derived from the western and central south african hinterland dominated by deserts semi deserts and savannah regions rich in c4 and cam plants the northern sites congo fan area and northern angola basin which get most of their terrestrial material from the congo basin and the angolan highlands may also receive some material from the chad region very little aerosol from the african continent is transported to the most southerly sites in the cape basin as can be expected from the present position of the phytogeographic zones the carbon isotopic signatures of the n alkanes and n alkanols both become isotopically more enriched in 13c from north to south the results of the study suggest that this combination of pollen data and compound specific isotope geochemical proxies can be effectively applied in the reconstruction of past continental phytogeographic developments

forcing of tropical atlantic sea surface temperatures during the mid pleistocene transition 1 we compare a new mid pleistocene sea surface temperature sst record from the eastern tropical atlantic to changes in continental ice volume orbital insolation atlantic deepwater ventilation and southern ocean front positions to resolve forcing mechanisms of tropical atlantic sst during the mid pleistocene transition mpt at the onset of the mpt a strong tropical cooling occurred the change from a obliquity to a eccentricity dominated cyclicity in the tropical sst took place at about 650 kyr bp in orbital cycles tropical sst changes significantly preceded continental ice volume changes but were in phase with movements of southern ocean fronts after the onset of large amplitude 100 kyr variations additional late glacial warming in the eastern tropical atlantic was caused by enhanced return flow of warm waters from the western atlantic driven by strong trade winds pronounced 80 kyr variations in tropical sst occurred during the mpt in phase with and likely directly forced by transitional continental ice volume variations during the mpt a prominent anomalous long term tropical warming occurred likely generated by extremely northward displaced southern ocean fronts while the overall pattern of global climate variability during the mpt was determined by changes in mean state and frequency of continental ice volume variations tropical atlantic sst variations were primarily driven by early changes in subantarctic sea ice extent and coupled southern ocean frontal positions

the impact of african aridity on the isotopic signature of atlantic deep waters across the middle pleistocene transition abstract a high resolution analysis of benthic foraminifera as well as of aeolian terrigenous proxies extracted from a 37 m long marine core located off the mauritanian margin spanning the last 1 2 ma documents the possible link between major continental environmental changes with a shift in the isotopic signature of deep waters around 1 0 0 9 ma within the so called mid pleistocene transition mpt time period the increase in the oxygen isotopic composition of deep waters as seen through the benthic foraminifera 18o values is consistent with the growth of larger ice sheets known to have occurred during this transition deep water mass 13c changes also estimated from benthic foraminifera show a strong depletion for the same time interval this drastic change in 13c values is concomitant with a worldwide 0 3 decrease observed in the major deep oceanic waters for the mpt time period the phase relationship between aeolian terrigeneous signal increase and this 13c decrease in our record as well as in other paleorecords supports the hypothesis of a global aridification amongst others processes to explain the deep water masses isotopic signature changes during the mpt in any case the isotopic shifts imply major changes in the end member 18o and 13c values of deep waters

links between the onset of modern walker circulation and the mid pleistocene climate transition sea surface temperatures ssts reconstructed from ocean drilling program sites 806 and 849 in the western and eastern equatorial pacific provide a history of the strength of the walker circulation between 1 5 and 0 5 ma a progressive cooling in the eastern equatorial pacific is paralleled by intensification of the equatorial zonal sst gradient that began 1 17 ma prior to the expansion of global ice volume associated with the mid pleistocene climate transition the ssts in the eastern equatorial pacific and the zonal gradient reached modern values by 0 9 ma we propose that this onset and intensification of the modern walker circulation reduced heat flux but increased moisture transport to high latitudes leading to the development of more extensive ice sheets and the shift toward the 100 ka world

underlying causes for long term global ocean δ13c fluctuations over the last 1 20 myr pleistocene stable carbon isotope 13c records from surface and deep dwelling foraminifera in all major ocean basins show two distinct long term carbon isotope fluctuations since 1 00 ma the first started around 1 00 ma and was characterised by a 0 35 decrease in 13c values until 0 90 ma followed by an increase of 0 60 lasting until 0 50 ma the subsequent fluctuation started with a 0 40 decrease between 0 50 and 0 25 ma followed by an increase of 0 30 between 0 25 and 0 10 ma here we evaluate existing evidence and various hypotheses for these global pleistocene 13c fluctuations and present an interpretation where the fluctuations most likely resulted from concomitant changes in the burial fluxes of organic and inorganic carbon due to ventilation changes and or changes in the production and export ratio our model indicates that to satisfy the long term stability of the pleistocene lysocline the ratio between the amounts of change in the organic and inorganic carbon burial fluxes would have to be close to a 1 1 ratio as deviations from this ratio would lead to sizable variations in the depth of the lysocline it is then apparent that the mid pleistocene climate transition which apart from the glacial cycles represents the most fundamental change in the pleistocene climate was likely not associated with a fundamental change in atmospheric pco2 while recognising that high frequency glacial interglacial cycles are associated with relatively large 100 ppmv changes in pco2 our model scenario with burial changes close to a 1 1 ratio produces a maximum long term variability of only 20 ppmv over the fluctuation between 1 00 and 0 50 ma

neutral winds in the lower thermosphere from dynamics explorer 2 doppler line profile measurements of the oi 557 7 nm green line emission made by the fabry perot interferometer on dynamics explorer 2 have provided altitude profiles of the meridional component of the lower thermospheric neutral wind the wind inversion technique of nardi 1991 has been used to extract the neutral wind profiles from the line of sight measurements individual 557 7 nm doppler line profiles and inverted volume emission rate and neutral wind profiles are presented neutral wind measurements from the 120 km altitude level obtained on multiple orbital passes over the summer hemisphere polar region have been merged to produce a synthesized averaged vector wind field in geomagnetic coordinates the wind pattern exhibits a region of anticyclonic vorticity in the daytime sector of the magnetic polar cap averaged winds of 300 m sec in the equatorial direction are observed in the early morning sector the satellite winds are in reasonable agreement with the predictions of the ncar and ucl thermosphere general circulation models with significant regional discrepancies evident in both magnitude and direction

on the timing and forcing mechanisms of late pleistocene glacial terminations insights from a new high resolution benthic stable oxygen isotope record of the eastern mediterranean abstract benthic oxygen isotope records of deep marine sedimentary archives have yielded a wealth of information regarding ice sheet dynamics and climate change during the pleistocene however since they often lack independent age control these records are generally bound by a fixed phase relationship between orbital forcing and the climate response e g ice volume changes we present the first long 1 2 ma benthic oxygen isotope record from the eastern mediterranean based on odp sites 967 and 968 which clearly reflects the behavior of global climate on a glacial interglacial scale throughout the late pleistocene time period the age model for our record is based on tuning the elemental ratio of titanium versus aluminum ti al against insolation the ti al record is dominated by the precession related changes in northern african climate i e monsoonal forcing and hence largely independent of glacial interglacial variability we found the largest offset between our chronology and that of the widely applied open ocean stacked record lr04 lisiecki and raymo 2005 for t vii 624 ka which occurred 9 kyr earlier according to our estimates though in agreement with the aicc2012 d ice chronology of epica dome c bazin et al 2013 spectral cross correlation analysis between our benthic 18 o record and 65 n summer insolation reveals significant amounts of power in the obliquity and precession range with an average lag of 5 5 0 8 kyr for obliquity and 6 0 1 0 kyr for precession in addition our results show that the obliquity related time lag was smaller 3 0 3 3 kyr prior to 900 ka than after 5 7 1 1 kyr suggesting that on average the glacial response time to obliquity forcing increased during the mid pleistocene transition much later than assumed by lisiecki and raymo 2005 finally we found that almost all glacial terminations have a consistent phase relationship of 45 45 with respect to the precession and obliquity driven increases in 65 n summer insolation consistent with the general consensus that both obliquity and precession are important for deglaciation during the late pleistocene exceptions are glacial terminations t iiib t 36 and potentially t 32 and t vii t 24 and t 34 which show this consistent phase relationship only with precession only with obliquity our findings point towards an early 1200 ka onset of the mid pleistocene transition vice versa the timing of t vii which can only be explained as a response to obliquity forcing indicates that the transition lasted until at least after mis 15

early onset and tropical forcing of 100 000 year pleistocene glacial cycles between 1 5 and 0 6 myr ago the period of the earth s glacial cycles changed from 41 kyr the period of the earth s obliquity cycles to 100 kyr the period of the earth s orbital eccentricity1 2 which has a much smaller effect on global insolation the timing of this transition and its causes pose one of the most perplexing problems in palaeoclimate research3 here we use complex demodulation to examine the phase evolution of precession and semiprecession cycles the latter of which are phase coupled to both precession and eccentricity in the tropical and extra tropical atlantic ocean we find that about 1 5 myr ago tropical semiprecession cycles with periods of about 11 5 kyr started to propagate to higher latitudes coincident with a growing amplitude envelope of the 100 kyr cycles evidence from numerical models suggests that cycles of about 10 kyr in length may be required to explain the high amplitude of the 100 kyr cycles4 combining our results with consideration of a modern analogue we conclude that increased heat flow across the equator or from the tropics to higher latitudes around 1 5 myr ago strengthened the semiprecession cycle in the northern hemisphere and triggered the transition to sustained 100 kyr glacial cycles

obscuring of long eccentricity cyclicity in pleistocene oceanic carbon isotope records abstract long eccentricity 400 kyr cycles in carbon isotope records from the pacific and atlantic oceans and the mediterranean sea of the past 5 0 ma are compared all records show maximum 13c values 13cmax at eccentricity minima during the pliocene but this relationship obscured in the pleistocene after 1 6 ma in particular for the open ocean deep water 13c records since a clear anti phase relationship was set up between oceanic 18o and 13c in the 100 kyr band from this time we attribute the obscured 400 kyr signal to a major change in the oceanic carbon reservoir probably associated with restructure of the southern ocean a similar change occurred in the miocene at 13 9 ma when the 400 kyr cyclicity in 13c records flattened out together with a drastic cooling and antarctic ice sheet expansion a remarkable exception is the mediterranean surface water 13c record which remained paced by the long term eccentricity cycle throughout the pliocene and pleistocene suggesting a low latitude climatic origin of the 400 kyr signal that is independent of glacial interglacial forcing since the earth is currently passing through an eccentricity minimum it is crucial to understand the nature of the 13cmax events

early middle pleistocene transitions linking terrestrial and marine realms abstract marked by a progressive increase in the amplitude of climate oscillations an evolving waveform and a shift towards a quasi 100 ky frequency the early middle pleistocene transition empt previously known as the mid pleistocene transition or mid pleistocene revolution 1 4 0 4 ma represents a fundamental transformation in the earth s climate state the empt began with a substantial change in climate dynamics and ended with the mid brunhes event signaling the establishment of a new steady state the reasons for the empt while uncertain appear to involve a non linear response of the earth climate system the physical and biotic responses to this transition amplified by the growth of northern hemisphere ice sheets have been profound two important chronostratigraphic markers characterize the empt the jaramillo subchron 1 070 0 988 ma and the matuyama brunhes chron boundary 773 ka the latter has been chosen as the primary guide for the lower middle pleistocene subseries boundary as it lies at the approximate midpoint of the empt and aids in global recognition both in marine and terrestrial deposits the jaramillo subchron has received less attention but the late early pleistocene is important in europe because it saw the progressive transition from the villafranchian to galerian mammal faunas and expansion of hominins into western and northern europe the jaramillo subchron is represented by marine isotope stages mis 31 to 28 with mis 30 already showing the asymmetrical sawtooth pattern characteristic of the middle pleistocene indeed while variation in the 40 ky band obliquity remains strong throughout the empt low frequency variability begins at around 1250 1200 ky which coincides with a progressive increase in global ice volume against a backdrop of increasingly severe glacial cycles notably during mis 36 34 24 22 the so called 0 9 ma event 16 and 12 pronounced phases of warming are also documented globally including the super interglacial mis 31 the early phase of the empt is characterized by important glaciations beginning with mis 36 and continuing to mis 24 22 a major intensification of the east asian monsoon system intensification of loess deposition in northern europe development of open landscapes in western siberia increased fluvial incision higher amplitude sea level change and spread of large mammals across northern eurasia and a strong reduction in the north atlantic thermohaline circulation in europe the loss of thermophilous plant taxa during the empt and indeed throughout the quaternary is a reminder of the progressive cooling that took place here and elsewhere

variations in the western pacific warm pool across the mid pleistocene evidence from oxygen isotopes and coccoliths in the west philippine sea abstract we present planktonic foraminifera oxygen isotope and florisphaera profunda abundance data from the international marine global change study program images core md06 3050 which was collected in the west philippine sea on the margin of the western pacific warm pool wpwp our records reveal marked changes in the upper water structure in the kuroshio source region as early as 1 5 ma continuing through the mid pleistocene climate transition mpt these changes are evidenced by reconstructions of the thermocline based on planktonic foraminiferal oxygen isotope differences and the nutricline based on the relative abundance of the coccolithophore species florisphaera profunda in the kuroshio source region the evolution of the thermocline nutricline featured three prominent phases 1 phase i 1 5 1 1 ma which was characterized by low amplitude variations in a shallow thermocline 2 phase ii 1 1 0 8 ma which was characterized by high amplitude variations in a relatively shallow thermocline nutricline and 3 phase iii 0 8 0 5 ma which was characterized by low amplitude variations in a deep thermocline nutricline combined with the zonal sea surface temperature gradient in the tropical pacific the evolution of the upper water structure can be linked to tropical climatic changes across the mpt including the intensification of atmospheric circulation and a gradual cessation of the long term el nino like state the upper water structure of the wpwp was asymmetric before 0 8 ma with a shallow thermocline nutricline along the northern margin and a deep thermocline nutricline in the center of the wpwp and south china sea scs the modern wpwp was established by approximately 0 8 ma and the upper water structure has changed synchronously as a whole since that time a comparison of the 18 o values derived from globigerinoides ruber tests from the md06 3050 core with those from other cores in the western pacific suggests that the lower glacial interglacial g ruber 18 o values in md06 3050 before 0 8 ma could be related to the enhancement of the wpwp and to changes in atmospheric circulation patterns

evolution of a deep water ferromanganese nodule in the south china sea in response to pacific deep water circulation and continental weathering during the plio pleistocene abstract the south china sea scs is connected to the west pacific through a deep channel in the luzon strait thus the scs deep water is sensitive to the evolution of pacific ocean circulation which significantly influences the global climate system geochemical data pb isotope and redox sensitive elements data and magnetic data were determined for a fe mn nodule obtained from jiaolong seamount in the central scs these records reflect interactions between changes in ice sheets deep pacific circulation and weathering inputs to the deep scs during the pliocene and quaternary our results show that the scs deep water environment can be divided into three major stages stages 1 3 stage 1 4 8 1 4 ma was characterized by a well oxygenated pacific deep water pdw and lower dust inputs then moderate stable deep water ventilation and greater inputs of asian dust occurred during stage 2 1 4 0 9 ma during stage 3

the summer wind field between 80 and 93 km observed by the mst radar at poker flat alaska 65 n abstract results of an analysis of the summertime wind field between 80 93 km over poker flat alaska are presented the data were obtained using the large but as yet incomplete mst radar at poker flat and cover the periods 17 june 13 july 1979 and 22 june 22 july 1980 zonal and meridional mean wind profiles and tidal components during these periods are examined and are compared with other observations at comparable latitudes as well as with current theoretical profiles while our results agree reasonably closely with other observations and theory some discrepancies exist and are discussed in addition to the expected 8 12 and 24 h components of atmospheric motions we find strong evidence for a 16 h component particularly during the 1979 data period in addition we show examples of the average power spectrum of wind fluctuations from 3 min to 8 days these spectra not only show the expected tidal peaks but show also that the spectral energy density is continuous between the shortest 8 h t

a long term comparison of middle atmosphere winds measured at saskatoon 52 n 107 w by a medium frequency radar and a fabry perot interferometer since late 1988 a medium frequency radar mfr and an imaging fabry perot interferometer fpi have been operating continuously at saskatoon measuring winds and waves in the upper mesosphere and lower thermosphere when weather and auroral conditions permit the fpi measures doppler winds from the atomic oxygen oi 557 7 nm airglow layer centered at an altitude of about 97 km this study is similar to earlier comparisons between the mfr fpi systems except that it draws on 4 years of simultaneous observations because the mfr and fpi are somewhat mutually exclusive in their data acquisition rate real time comparisons of winds are often poor however with the much larger fpi data set now available rather better long term comparisons between the two systems can be made once again strong similarities in the mf radar and fpi doppler wind fields are observed although there are some differences these differences and the causes are discussed

the onset of major northern hemisphere glaciations and their impact on dinoflagellate cysts and acritarchs from the singa section calabria southern italy and dsdp holes 607 607a north atlantic abstract the climatic deterioration related to the onset of northern hemisphere glaciations circa 2 52 ma b p must have lead to reorganization and relocation of species associations and may have enhanced species turnover the present study investigates how this deterioration affects the dinoflagellate cyst and acritarch assemblages from two locations dsdp site 607 north atlantic and the singa section southern italy the records from these locations cover the interval from 2 8 to 2 2 ma with at least a 5 ka resolution and they have been correlated to the milankovitch periodicities on a cycle to cycle basis by means of integrated high resolution stable isotope calcium carbonate foraminiferal palynological and magnetostratigraphical datasets in the present study this high resolution stratigraphic framework is used for a detailed correlation of events occurring in each of the depositional sequences it also enables further assessment of the palaeoenvironmental preferences of some dinoflagellate cyst forms comparison of the two palynological records reveals a close correspondence in the timing of major assemblage changes and extinction events confirming their milankovitch cycle based correlation a close link between periods of northern hemisphere cooling at oxygen isotope stages 110 104 and 100 96 and increased dinoflagellate cyst turnover appears to be present for both dsdp site 607 and the singa section the turnover events can also be recognized in the records of planktic foraminifera and calcareous nannoplankton comparison of the singa section with site 607 and with other time equivalent marine palynological data sets shows that some oceanic taxa respond similarly over a large area the biostratigraphical implications are discussed notably the last occurrence of invertocysta lacrymosa appears to be a valuable marker for isotope stage 110 in the mediterranean and north atlantic

soil organic matter as an important contributor to late quaternary sediments of the tropical west african continental margin the contribution of soil organic matter som to continental margins is largely ignored in studies on the carbon budget of marine sediments detailed geochemical investigations of late quaternary sediments 245 0 ka from the niger and congo deep sea fans however reveal that corg ntot ratios and isotopic signatures of bulk organic matter 13corg in both fans are essentially determined by the supply of various types of som from the river catchments thus providing a fundamentally different interpretation of established proxies in marine sciences on the niger fan increased corg ntot and 13corg up to 17 were driven by generally nitrogen poor but 13c enriched terrigenous plant debris and som from c4 c3 vegetation entisol domains grass and tree savannah on young sandy soils supplied during arid climate conditions opposite humid climates supported drainage of c3 c4 vegetation alfisol ultisol domains forest and tree savannah on older developed clay bearing soils that resulted in lower corg ntot and 13corg 20 in the niger fan record sediments from the congo fan contain a thermally stable organic fraction that is absent on the niger fan this distinct organic fraction relates to strongly degraded som of old and highly developed kaolinite rich ferallitic soils oxisols that cover large areas of the congo river basin reduced supply of this nitrogen rich and 12c depleted som during arid climates is compensated by an elevated input of marine om from the high productive congo up welling area this climate driven interplay of marine productivity and fluvial som supply explains the significantly smaller variability and generally lower values of corg ntot and 13corg for the congo fan records this study emphasizes that ignoring the presence of som results in a severe underestimation of the terrigenous organic fraction leading to erroneous paleoenvironmental interpretations at least for continental margin records furthermore burial of som in marine sediments needs more systematic investigation combining marine and continental sciences to assess its global relevance for long term sequestration of atmospheric co2

high latitude mesopause neutral winds and geomagnetic activity a cross correlation analysis a cross correlation analysis of horizontal winds at 87 km obtained by the poker flat mesosphere stratosphere troposphere mst radar and college magnetometer horizontal component fluctuations has been performed on 3 years of summertime data no consistent significant peak in the average 4 day estimate cross correlation results is apparent from year to year individual estimates similarly do not show evidence of a peak in cross correlation at a variable time lag during geomagnetically active intervals in addition the 1 day 24 and 12 hour wave amplitudes and phases and average zonal and meridional winds do not vary significantly and consistently with the daily averaged magnetometer horizontal component fluctuations or with the standard deviation thereof the interval following the july 13 1982 polar cap absorption event and geomagnetic storm however shows a different cross correlation estimate behavior and is characterized by significantly more westward zonal winds and enhanced 24 hour zonal wind amplitude

quantifying the role of biosphere atmosphere feedbacks in climate change coupled model simulations for 6000 years bp and comparison with palaeodata for northern eurasia and northern africa the lmd agcm was iteratively coupled to the global biome1 model in order to explore the role of vegetation climate interactions in response to mid holocene 6000 y bp orbital forcing the sea surface temperature and sea ice distribution used were present day and co2 concentration was pre industrial the land surface was initially prescribed with present day vegetation initial climate anomalies differences between agcm results for 6000 y bp and control were used to drive biome1 the simulated vegetation was provided to a further agcm run and so on results after five iterations were compared to the initial results in order to identify vegetation feedbacks these were centred on regions showing strong initial responses the orbitally induced high latitude summer warming and the intensification and extension of northern hemisphere tropical monsoons were both amplified by vegetation feedbacks vegetation feedbacks were smaller than the initial orbital effects for most regions and seasons but in west africa the summer precipitation increase more than doubled in response to changes in vegetation in the last iteration global tundra area was reduced by 25 and the southern limit of the sahara desert was shifted 2 5 n north to 18 n relative to today these results were compared with 6000 y bp observational data recording forest tundra boundary changes in northern eurasia and savana desert boundary changes in northern africa although the inclusion of vegetation feedbacks improved the qualitative agreement between the model results and the data the simulated changes were still insufficient perhaps due to the lack of ocean surface feedbacks

the mid pleistocene climate transition a deep sea carbon isotopic perspective five 13c records from the deep ocean extending back to 1 3 ma were examined in order to constrain changes in mean ocean carbon isotope composition and thermohaline circulation over the 41 to 100 ka climate transition these data show that significant perturbations in mean ocean carbon chemistry were associated with the mid pleistocene climate transition notable features of the last 1 3 myr are 1 a pronounced 0 3 decrease in mean ocean 13c between 0 9 and 1 0 myr followed by a return to pre 1 0 ma values by 400 ka b p which we propose was due to the onetime addition of isotopically depleted terrestrial carbon to the ocean possibly associated with an increase in global aridity and decrease in the size of the biosphere across the 41 to 100 ka transition 2 no change in the atlantic pacific a p 13c gradient over the last 1 3 myr suggesting no change in mean ocean nutrient content accompanied the addition of light carbon and 3 stronger vertical nutrient fractionation in the north atlantic in the middle pleistocene between sites 607 and 552 suggesting weaker north atlantic deep water formation at this time relative to the early and late pleistocene we also find evidence for a more pronounced deep recirculation gyre in the western north atlantic basin in the early brunhes as evidenced by aging of deep northern basin water site 607 relative to deep water in the equatorial atlantic site 664

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

exploring the structure of the mid pleistocene revolution with advanced methods of time series analysis the mid pleistocene climate transition is a complex global change leading to late pleistocene ice ages with increased mean ice volume and dominant 100 ka cycle a thorough understanding of this transition demands quantitative investigations in the time and frequency domains and in the stochastic domain three methods of time series analysis are presented which have been adapted for this purpose they are tested by means of predefined artificial time series and applied to benthic oxygen isotope d18o records which serve as ice volume indicator results are as follows a the time dependent mean shows an increase of 0 35 vs pdb from 942 to 892 ka b evolutionary spectral analysis reveals an abrupt in crease of 100 ka cycle amplitude at approximately 650 ka c probability density function exhibits a bifur cation behavior at approximately 725 ka these find ings point to a multiple transition from a more linear climate system to a strong nonlinear system the signif icant lead of the transition in mean in relation to the 100 ka amplitude change and bifurcation is left open for explanation

frequency spectra and paleoclimatic variability of the high resolution 30 1450 ka funza i pollen record eastern cordillera colombia the evolution of orbital periodicities during the quaternary has been studied in the 30 1450 ka funza i pollen record from cores through the sedimentary basin of bogota eastern cordillera colombia the 1178 pollen samples analysed between 2 90 and 340 00 m generate 5 time series with an average time resolution of ca 1200 years our geochronological framework is based on fission track ages on zircon in combination with correlation of the pollen record with the oxygen isotope record of odp site 677 from the eastern pacific the 5 data sets were analysed in the frequency domain with maximum entropy spectrum analysis mesa and thomson multi taper spectrum analysis tmt using a moving 400 ka window with steps of 20 ka frequencies closely related to the milankovitch theory were detected in all 5 data sets the 100 ka period in the arboreal pollen record is restricted to the last ca 800 ka of the quaternary at a confidence level largely higher than 90 periodicities close to 23 ka occur throughout the record at a high significance level above 90 and are strongest in the subparamo data a statistically significant period centred at ca 40 ka also occurs in the funza i record four frequency bands centred at ca 30 ca 15 ca 13 and ca 10 ka were also detected the 5 principle data sets from the funza i pollen record reveal an evolution of orbital frequencies in the middle and late quaternary which are in general agreement with other marine e g imbrie et al 1984 and continental e g kukla et al 1990 records

taraxerol and rhizophora pollen as proxies for tracking past mangrove ecosystems angola basin and cape basin southeast atlantic surface sediments and sediment cores show that maxima in the abundance of taraxerol relative to other land derived lipids covary with maxima in the relative abundance of pollen from the mangrove tree genus rhizophora and that in the surface sediments offshore maxima in the relative abundance of taraxerol occur at latitudes with abundant coastal mangrove forests together with the observation that rhizophora mangle and rhizophora racemosa leaves are extraordinarily rich in taraxerol this strongly indicates that taraxerol can be used as a lipid biomarker for mangrove input to the se atlantic the proxy environment relations for taraxerol and rhizophora pollen down core show that increased taraxerol and rhizophora pollen abundances occur during transgressions and periods with a humid climate these environmental changes modify the coastal erosion and sedimentation patterns enhancing the extent of the mangrove ecosystem and or the transport of mangrove organic matter offshore analyses of mid pleistocene sediments show that interruption of the pattern of taraxerol maxima during precession minima occurs almost only during periods of low obliquity this demonstrates the complex environmental response of the interaction between precession related humidity cycles and obliquity related sea level changes on mangrove input

early middle pleistocene transitions an overview and recommendation for the defining boundary the early middle pleistocene transition c 1 2 0 5 ma sometimes known as the mid pleistocene revolution represents a major episode in earth history low amplitude 41 ka obliq uity forced climate cycles of the earlier pleistocene were replaced progressively in the later pleistocene by high amplitude 100 ka cycles these later cycles are indicative of slow ice build up and subsequent rapid melting and imply a transition to a strongly non linear forced climate system changes were accompanied by substantially increased global ice volume at 940 ka these climate transformations particularly the increasing severity and duration of cold stages have had a pro found effect on the biota and the physical landscape especially in the northern hemisphere this review assesses and integrates the marine and terrestrial evidence for change across this transition based on the literature and especially the following 17 chapters in the present volume orbital and non orbital climate forcing palaeoceanography stable isotopes organic geochemistry marine micropalaeontology glacial history loess palaeosol sequences pollen analysis large and small mammal palaeoecology and stratigraphy and human evolution and dispersal are all considered and a series of discrete events is identified from marine isotope stage mis 36 c 1 2 ma to mis 13 c 540 460 ma of these the cold mis 22 c 880 870 ka is perhaps the most profound however we here endorse earlier views that on practical grounds the matuyama brunhes palaeomagnetic chron boundary mid point at 773 ka with an estimated duration of 7 ka would serve as the best overall guide for establishing the early middle pleistocene subseries boundary

major pleistocene stages in a carbon perspective the south china sea record and its global comparison 1 carbon isotope sequences at ocean drilling program site 1143 south china sea reveal a long term cyclicity of 500 kyr that is superimposed on the glacial cycles and is present in long 13c sequences from all oceans the quaternary 13c record is punctuated by four 13c maximum events 13cmax i which began in marine isotope stage mis 3 around 50 60 kyr ago 13cmax ii mis 13 0 47 0 53 ma 13cmax iii mis 27 29 0 97 1 04 ma and 13cmax vi mis 53 57 1 55 1 65 ma as the same cyclicity is also found in carbonate curves the 13cmax events must denote major reorganization in the carbon reservoir of the global ocean they also are associated with major changes in glacial cyclicity such as the mid brunhes event following 13cmax ii and the mid pleistocene revolution following 13cmax iii which in turn were associated with expansion of the ice sheets from a carbon perspective therefore the quaternary period has passed through three major stages and each appears to represent a further step in ice cap development

organic matter in river influenced continental margin sediments the land ocean and climate linkage at the late quaternary congo fan odp site 1075 1 late quaternary sections 1 2 ma of odp site 1075 from the congo deep sea fan are investigated to reconstruct variations of terrigenous organic matter supply to the eastern equatorial atlantic to characterize the organic matter om with regard to marine and terrigenous amounts we used elemental analysis c n s stable carbon isotopes bulk 13corg rock eval pyrolysis and terrigenous biomarkers lignin phenols from cuo oxidation the records of total organic carbon toc contents corg ntot ratios bulk om degradation rates corg corg and the ratios of hydrocarbons hc from low mature versus hc from high mature om lm hm reveal pronounced cyclic changes in om abundance preservation and reactivity that are closely related to the precessional controlled record of insolation and thus to variations in upwelling intensity and fluvial run off primary productivity off the congo is stimulated by both enhanced nutrient supply in response to trade induced upwelling during arid african climates insolation minima and fluvial nutrient delivery during humid stages following insolation maxima especially due to the contribution of dissolved silica that is taken up preferably by diatoms however results stemming from a multiparameter approach reveal that the fluvial supply of degraded om and black carbon bc associated with fine grained sediments from soil erosion is a decisive factor for the preservation of marine om and in addition significantly influences the geochemical signature of bulk and terrigenous om riverine and eolian supply of c4 plant matter as well as enhanced concentrations of bc during arid and arid to humid transitional climate stages may lead to a severe underestimation of terrigenous organic carbon if its amount is calculated from bulk isotopic ratios using binary end member models during the humid stages it is the massive supply of 13c enriched soil om with low corg ntot ratios that may suggest a mainly marine composition of bulk om in fact terrigenous om governs bulk om geochemical signatures in the sediments of the congo deep sea fan a result that is contradictory to earlier studies especially to the conventional interpretation of the bulk 13corg signal

a coupled climate ice sheet model applied to the quaternary ice ages a coupled climate ice sheet model is used in an attempt to simulate the northern hemispheric ice sheet volume variations implied by deep sea core records over the last several 105 years the climate model consists of a global one level diffusive energy balance equation with seasonal variation and land ocean contrast using a severely truncated series of associated legendre functions the ice sheet model uses a standard vertically averaged flow law and predicts ice thickness in a north south cross section bedrock deformation under the ice is included as linear flow confined to a thin asthenospheric channel the climate model is tuned to the modern climate and tested against results from atmospheric general circulation models for 18 000 and 10 000 yr b p it is suggested that the lack of sea ice variations causes the biggest departures from the gcm results the sensitivities to the orbital perturbations of the coupled model and of the ice sheet model alone with a prescribed snow budget distribution are examined some qualitative differences are found in the latitudinal forms of these sensitivities despite these differences however the two types of models produce similar ice age simulations over the last 700 thousand years in response to the orbital perturbations in particular fairly realistic simulations with strong 100 kyr cycles similar to those obtained by adding an ice calving mechanism to the ice sheet model in pollard 1982a are again produced in the coupled model