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

impact of restriction of the atlantic mediterranean gateway on the mediterranean outflow water and eastern atlantic circulation during the messinian 1 messinian foraminiferal stable oxygen and carbon isotopes of the montemayor 1 core guadalquivir basin sw spain have been investigated this record is exceptional to study the mediterranean outflow water mow impact on the atlantic meridional overturning circulation amoc and global climate during the messinian because the core is near the guadalhorce corridor the last betic gateway to be closed during the early messinian our results allow dating accurately its closure at 6 18 ma constant benthic 18o values high difference between benthic and planktonic 18o and low sedimentation rates before 6 18 ma indicate the presence of a two layer water column with bottom winnowing due to an enhanced mediterranean outflow current the enhanced contribution of dense mow to the north atlantic ocean likely fostered the formation of north atlantic deep water nadw after 6 18 ma benthic 18o values parallel that of the global glacioeustatic curve the difference between benthic and planktonic 18o is low and sedimentation rates considerably increased this indicates a good vertical mixing of the water column interruption of the mow and a dominant glacioeustatic control on the isotopic signatures according to the role of mow in the modern atlantic thermohaline circulation the reduction of the mow after the closure of the guadalhorce corridor might have resulted in a decreased nadw formation rate between 6 0 and 5 5 ma weakening the amoc and promoting northern hemisphere cooling after the gibraltar strait opening the restoration of the mow and related salt export from the mediterranean could have promoted an enhanced nadw formation

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

the chemistry of quartz in granitic pegmatites of southern norway petrogenetic and economic implications trace element concentrations in quartz from 188 granitic pegmatites in the froland and evje iveland pegmatite fields southern norway have been determined to establish exploration targets for high purity quartz and to gain a better understanding of the genesis of pegmatites hosting these deposits both pegmatite fields were formed during the sveconorwegian grenvillian orogeny 1145 900 ma at the western margin of the fennoscandian shield in situ raster analyses within single quartz crystals were undertaken by laser ablation inductively coupled plasma mass spectrometry la icp ms spot size 75 m to assess levels of lattice bound impurities rather than mineral and fluid inclusions that are relatively easily removed during high purity quartz processing quartz in the froland pegmatites has relatively pure and homogeneous compositions containing 46 24 gg 1 al 8 3 gg 1 ti 1 4 0 8 gg 1 ge and 11 7 gg 1 li the ti in quartz geothermobarometer gives an average pegmatite crystallization temperature of 537 39 c temperature estimates are highest along the northwestern margin of the pegmatite field 550 c whereas the most differentiated pegmatites occur toward the northeast the area of greatest economic potential for high purity quartz lies just north of the central part of the field where individual pegmatites contain 1 million metric tons mt quartz with low average trace element contents of 67 11 gg 1 from mineral chemical criteria and a range of other geologic factors we propose that pegmatite melts in the froland field were generated by fluid present crustal melting at about 1060 ma in zones of localized high strain deformation during progressive thrusting along the porsgrunn kristiansand fault zone quartz in the evje iveland pegmatites has more variable compositions with 69 57 gg 1 al 19 11 gg 1 ti 2 3 1 8 gg 1 ge and 7 5 gg 1 li from its ti content it crystallized at temperatures of 613 70 c the regional spatial distribution of ti in quartz temperatures appears irregular mainly due to the scattered distributions of chemical evolved pegmatites with amazonite cleavelandite replacement zones which show crystallization temperatures down to 442 c quartz from the evje iveland pegmatites is unlikely to be of current economic interest due to its moderate to high trace element contents heterogeneous chemistry and low volume the evje iveland pegmatites show no apparent genetic link to a granite intrusion instead they probably formed as a result of partial melting at the depth of their amphibolite country rocks at around 910 ma this is related to a regional low pressure high temperature metamorphic event at about 930 to 920 ma

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

climate modelling sensitivity experiments for the messinian salinity crisis abstract the repeated isolation of the atlantic ocean during the messinian led to at least the partial desiccation of the mediterranean sea and to the deposition of massive evaporites messinian salinity crisis overall proxy data do not indicate dramatic climatic changes in the mediterranean region for the time of the messinian salinity crisis but a constant climate seems to be unrealistic at first sight to analyse the climate response to environmental changes in the mediterranean region during the messinian salinity crisis we perform climate modelling sensitivity experiments as a reference base we use a tortonian simulation tort and simulate three messinian sensitivity scenarios 1 the mediterranean sea surface 1500 m lower than the normal sea level msc lowsea 2 the mediterranean basin completely desiccated the resulting land surface 1500 m lower and covered by grassland vegetation msc lowgrass and 3 the mediterranean sea simply replaced by grassland vegetation msc grass all sensitivity experiments represent extreme scenarios for analysis of general patterns of messinian climate change in msc lowsea mean annual temperatures in the mediterranean basin increase by 2 c and surrounding regions get cooler by up to 3 c as compared to tort the lowering of the mediterranean sea level increases the annual precipitation in the south western part of europe and in north western africa up to 1000 mm a in msc lowgrass as compared to tort the mediterranean basin strongly heats up by 7 c while temperatures in the surrounding areas do not change more than 2 c the precipitation in the mediterranean basin significantly decreases up to 600 mm a precipitation in the areas surrounding the mediterranean basin does not change substantially in msc lowgrass but rainfall in w africa increases up to 600 mm a in msc grass as compared to tort temperatures in the mediterranean region increase by 4 c this is twice as high as the temperature increase which resulted from lowering the mediterranean sea surface in msc lowsea annual rainfall over the mediterranean basin in msc grass is 400 mm a lower than the rainfall in tort proxy based climate reconstructions for the time of the messinian salinity crisis indicate no dramatic climatic changes around the mediterranean in contrast to this for eastern n africa and eastern europe climate changes are indicated the msc lowsea and msc lowgrass sensitivity experiments show that the strong environmental changes in the mediterranean realm during the msc did not necessarily cause strong climatic changes at the margins of the mediterranean basin therefore the present modelling studies are in agreement with climate proxy data from the mediterranean region additionally our results principally agree with the climate changes inferred from the fossil record of central and eastern europe for eastern n africa our modelling studies contradict proxy data based on our results weak climatic changes indicated by the fossil record at the mediterranean coastlines are realistic

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

correlation of late miocene to early pliocene sequences between the mediterranean and north atlantic ocean drilling program odp site 982 in the north atlantic contains a complete latest miocene to early pliocene section that was tuned to the astronomical timescale by correlating the record of gamma ray attenuation gra bulk density to summer insolation at 65 n and the benthic 18o signal to orbital obliquity for the interval from 4 6 to 7 5 ma the astronomical tuning of the site 982 record permits a direct bed to bed correlation to the cyclostratigraphy of messinian sections in the mediterranean krijgsman et al 1999a 2001 the benthic 18o signal at site 982 records a latest miocene glacial period that lasted from 6 26 to 5 50 ma and consisted of 18 glacial to interglacial oscillations that were controlled by the 41 kyr cycle of obliquity although the intensification of glaciation at 6 26 ma may have contributed to the restriction of the mediterranean it preceded the depositional onset of the lower evaporite unit at 5 96 ma by some 300 kyr the transition from stage tg12 to tg11 at 5 5 ma marks the end of the latest miocene glacial period and precedes the miocene pliocene boundary by 170 kyr although benthic 18o values are relatively low and 18o of bulk carbonate reaches a minimum at the miocene pliocene boundary at 5 33 ma there is no single event that would indicate deglaciation and sea level rise as the cause of the reflooding of the mediterranean we conclude that glacioeustatic changes alone were not responsible for either the start or end of evaporite deposition during the messinian suggesting that tectonic or local climate changes in the mediterranean region were the dominant cause s

assessing orbitally forced interglacial climate variability during the mid pliocene warm period abstract the traditional view of the pliocene is one of an epoch with higher than present global mean annual temperatures 2 to 3 c and stable climate conditions published data model comparisons for the mid pliocene warm period mpwp 3 3 to 3 million years ago have identified specific regions of concordance and discord between climate model outputs and marine terrestrial proxy data due to the time averaged nature of global palaeoenvironmental syntheses it has been hypothesised that climate variability during interglacial events within the mpwp could contribute to site specific data model disagreement the hadley centre coupled climate model version 3 hadcm3 is used to assess the nature of climate variability around two interglacial events within the mpwp that have different characteristics of orbital forcing marine isotope stages km5c and k1 model results indicate that 20 kyr on either side of the mis km5c orbital forcing produced a less than 1 c change in global mean annual temperatures regionally mean annual surface air temperature sat variability can reach 2 to 3 c seasonal variations exceed those predicted for the annual mean and can locally exceed 5 c simulations 20 kyr on either side of mis k1 show considerably increased variability in relation to km5c we demonstrate that orbitally forced changes in surface air temperature during interglacial events within the mpwp can be substantial and could therefore contribute to data model discord this is especially likely if proxies preserve growing season rather than mean annual temperatures model results indicate that peak mis km5c and k1 interglacial temperatures were not globally synchronous highlighting leads and lags in temperature in different regions this highlights the potential pitfalls in aligning peaks in proxy derived temperatures across geographically diverse data sites and indicates that a single climate model simulation for an interglacial event is inadequate to capture peak temperature change in all regions we conclude that the premise of sustained global warmth and stable pliocene climate conditions is incomplete we also contend that the likely nature of pliocene interglacial climate variability is more akin to interglacial events within the quaternary where the character of interglacials is known to be diverse in the future the utility of pliocene data model comparisons is dependent upon 1 establishing precise chronology of the proxy data 2 providing climate models with fully proxy consistent boundary conditions and 3 in utilising ensembles of climate simulations that can adequately capture orbital variability around any studied interval

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

late miocene stable isotope stratigraphy of se atlantic odp site 1085 relation to messinian events abstract high resolution benthic oxygen isotope and xrf fe and ca records from site 1085 drilled in the mid cape basin odp leg 175 are used to investigate global climate changes during the late miocene in relation to messinian geological events the cyclic fluctuations of the time series at site 1085 enable us to establish a reliable chronology for the time interval 7 3 4 7 ma spectral analysis of the 18o record indicates that the 41 kyr period of orbital obliquity dominates the late miocene record a global climate record was extracted from the oxygen isotopic composition of benthic foraminifera both long and short term variabilities in the climate record are discussed in terms of sea level and deep water temperature changes the time interval 7 3 6 25 ma characterized by low amplitude 18o variations is followed by a period marked by maximum in the 18o values 6 25 5 57 ma at about 5 56 ma a rapid decrease in 18o values is documented that may reflect a warming of deep water temperature associated with a global warming period comparison between the timing of the oceanic isotope events and the chronology of the mediterranean salinity crisis suggest that global eustatic processes were not essential in the mediterranean salinity crisis history from our data we infer that the global warmth documented in the early mid pliocene probably started during the late miocene at 5 55 ma at the same time the onset of evaporite deposition in the central basin of the mediterranean sea took place sharp changes in the sedimentation rates mainly driven by terrigenous input at this site are observed during the messinian stage

a modeling perspective on spatial and temporal variations in messinian evaporite deposits abstract during the messinian salinity crisis msc evaporite dominated sequences formed in marginal and deep basins of the mediterranean sea in the marginal basins the onset of the msc is synchronous and a single depositional framework fits all sequences in contrast msc sequences of the western and eastern deep basins appear to comprise a different number of units and differ greatly in thickness even though there exist numerous scenarios for deposition in the marginal and deep basins the link between the two settings is difficult and scenarios are rarely quantitatively supported we employ a simple box model for the messinian mediterranean to examine the causes of 1 spatial variation in thickness and 2 differences in the time of onset of deposition model results are compared with actual observations on the msc sequences the results show that a large connection between the western and eastern basin is necessary for and some degree of water column stratification is conducive to synchronous onset of the msc in the marginal basins moreover halite deposits in the deep basins are likely to be coeval and have formed in 60 ka after a further restriction of the atlantic mediterranean connection during the msc but without a significant sea level drop a difference in the net salt gain per unit volume caused the different halite deposition rates in the two basins a scenario with only a simple restriction of the atlantic mediterranean connection during the late miocene without significant changes in the mediterranean sea level the fresh water budget or the size of the strait of sicily is able to explain the synchronous onset of the msc the synchronous marginal evaporite formation and the differences in the deep basinal sequences

a reconstruction of late miocene mediterranean circulation patterns using benthic foraminifera abstract extensive research on the late miocene mediterranean has solved a number of questions concerning the development of the area but questions remain on for instance the mediterranean water circulation patterns knowledge of preferably quantitative oxygen contents of water masses could be of help to reconstruct paleo circulation and understand how this contributed to the development of the mediterranean messinian salinity crisis msc bottom water oxygenation is usually estimated qualitatively or semi quantitatively at best from abundances of infaunal benthic foraminifera from stable carbon isotope data or redox sensitive elements we present data from six mediterranean land sections and one section located at the atlantic side of the rifian corridor as an atlantic reference location we introduce a semi quantitative reconstruction of oxygen levels at the sediment water interface employing a simple index that operates on a scale from 1 low oxygen to 5 normal to high oxygen using this method we present a tentative reconstruction of the mediterranean water circulation in the period preceding the continuous development towards the msc which started at 7 17 ma we found that during the late miocene an anti estuarine circulation was likely quite comparable to the modern pattern deep water formation appears to have existed in the central northeastern part of the basin around 7 2 ma constriction of the rif corridor morocco led to restricted exchange of mediterranean and atlantic water masses a reduction of the deep circulation and decreasing bottom water ventilation deep water formation weakened and the mediterranean hydrography changed thoroughly eventually contributing to the development of the msc

middle to late miocene oxygen isotope stratigraphy of odp site 1085 se atlantic new constrains on miocene climate variability and sea level fluctuations abstract the middle miocene 18o increase represents a fundamental change in earth s climate system due to a major expansion and permanent establishment of the east antarctic ice sheet accompanied by some effect of deepwater cooling the long term cooling trend in the middle to late miocene was superimposed by several punctuated periods of glaciations mi events characterized by oxygen isotopic shifts that have been related to the waxing and waning of the antarctic ice sheet and bottom water cooling here we present a high resolution benthic stable oxygen isotope record from odp site 1085 located at the southwestern african continental margin that provides a detailed chronology for the middle to late miocene 13 9 7 3 ma climate transition in the eastern south atlantic a composite fe intensity record obtained by xrf core scanning odp sites 1085 and 1087 was used to construct an astronomically calibrated chronology based on orbital tuning the oxygen isotope data exhibit four distinct 18o excursions which have astronomical ages of 13 8 13 2 11 7 and 10 4 ma and correspond to the mi3 mi4 mi5 and mi6 events a global climate record was extracted from the oxygen isotopic composition both long and short term variabilities in the climate record are discussed in terms of sea level and deep water temperature changes the oxygen isotope data support a causal link between sequence boundaries traced from the shelf and glacioeustatic changes due to ice sheet growth spectral analysis of the benthic 18o record shows strong power in the 400 kyr and 100 kyr bands documenting a paleoceanographic response to eccentricity modulated variations in precession a spectral peak around 180 kyr might be related to the asymmetry of the obliquity cycle indicating that the response of the dominantly unipolar antarctic ice sheet to obliquity induced variations probably controlled the middle to late miocene climate system maxima in the 18o record interpreted as glacial periods correspond to minima in 100 kyr eccentricity cycle and minima in the 174 kyr obliquity modulation strong middle to late miocene glacial events are associated with 400 kyr eccentricity minima and obliquity modulation minima thus fluctuations in the amplitude of obliquity and eccentricity seem to be the driving force for the middle to late miocene climate variability

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

mediterranean climate and oceanography and the periodic development of anoxic events sapropels mediterranean sapropels are layers with elevated organic carbon concentrations that contrast with surrounding sediments which are organic poor sapropels occur quasi periodically in sedimentary sequences of the last 13 5 million years and exist both in the eastern and western mediterranean sub basins they have been the subject of extensive study based on records from both short conventional and long ocean drilling program sediment cores and from a wide variety of uplifted marine sediment sequences on the basin margins and islands previous syntheses in the 1990s and 2000s have discussed how the formation of sapropels is commonly ascribed to deep sea anoxia enhanced export productivity or a combination of these effects however a wealth of new evidence and insights has emerged during the past 1 2 decades based on traditional and novel proxy data as well as modelling which has revealed intriguing new aspects and nuances to the reconstructed conditions hence it is timely to present a new synthesis of current understanding of the processes behind the formation of sapropels which have over the past decade also become a matter of commercial interest in sub salt hydrocarbon exploration in this review we present a context of modern mediterranean climate and oceanography followed by an integrated assessment of the growing understanding of climatological and ocean circulation changes that were associated with sapropel deposition we find that sapropels predominantly formed during astronomically timed episodes when climatic and oceanographic conditions and ecological responses broadly preconditioned the basin for sapropel deposition there is strong correspondence with times of monsoon intensification fuelling runoff from north africa into the mediterranean sea while preconditioning due to sea level rise and regional precipitation and runoff may have contributed as well within these broad episodes of surface buoyancy gain and resultant decline in deep water ventilation specific deposition under dysoxic anoxic or even euxinic conditions occurred within a clearly dynamic system that was characterised by complex spatial and depth dependent patterns gradients with distinct temporal variability on at least decadal to centennial millennial timescales in the final section we evaluate the implications of different modes of deep water removal from silled basins to investigate why sapropels are more frequently and often more intensely developed in the eastern mediterranean than in the western mediterranean

late cretaceous to early quaternary organic sedimentation in the eastern equatorial atlantic abstract reconstructing the long term evolution of organic sedimentation in the eastern equatorial atlantic odp leg 159 provides information about the history of the climate ocean system sediment accumulation and deposition of hydrocarbon prone rocks the recovery of a continuous 1200 m long sequence at odp site 959 covering sediments from albian to the present day about 120 ma makes this position a key location to study these aspects in a tropical oceanic setting new high resolution carbon and pyrolysis records identify three main periods of enhanced organic carbon accumulation in the eastern tropical atlantic i e the late cretaceous the eocene oligocene and the pliocene pleistocene formation of upper cretaceous black shales off west africa was closely related to the tectono sedimentary evolution of the semi isolated deep ivorian basin north of the cote d ivoire ghana transform margin their deposition was confined to certain intervals of the last two cretaceous anoxic events the early turonian oae2 and the coniacian santonian oae3 organic geochemical characteristics of laminated coniacian santonian shales reveal peak organic carbon concentrations of up to 17 and kerogen type i ii organic matter which qualify them as excellent hydrocarbon source rocks similar to those reported from other marginal and deep sea basins a middle to late eocene high productivity period occurred off equatorial west africa porcellanites deposited during that interval show enhanced total organic carbon toc accumulation and a good hydrocarbon potential associated with oil prone kerogen deposition of these toc rich beds was likely related to a reversal in the deep water circulation in the adjacent sierra leone basin accordingly outflow of old deep waters of southern ocean origin from the sierra leone basin into the northern gulf of guinea favored upwelling of nutrient enriched waters and simultaneously enhanced the preservation potential of sedimentary organic matter along the west african continental margin a pronounced cyclicity in the carbon record of oligocene lower miocene diatomite chalk interbeds indicates orbital forcing of paleoceanographic conditions in the eastern equatorial atlantic since the oligocene miocene transition a similar control may date back to the early oligocene but has to be confirmed by further studies latest miocene early pliocene organic carbon deposition was closely linked to the evolution of the african trade winds continental upwelling in the eastern equatorial atlantic ocean chemistry and eustatic sea level fluctuations reduction in carbonate carbon preservation associated with enhanced carbon dissolution is recorded in the uppermost miocene 5 82 5 2 ma section and suggests that the latest miocene carbon record of site 959 documents the influence of corrosive deep waters which formed in response to the messinian salinity crisis furthermore sea level related displacement of higher productive areas towards the west african shelf edge is indicated at 5 65 5 6 5 55 5 2 4 8 ma in view of humid conditions in tropical africa and a strong west african monsoonal system around the miocene pliocene transition the onset of pronounced toc cycles at about 5 6 ma marks the first establishment of upwelling cycles in the northern gulf of guinea an amplification in organic carbon deposition at 3 3 ma and 2 45 ma links organic sedimentation in the tropical eastern equatorial atlantic to the main steps of northern hemisphere glaciation and testifies to the late pliocene transition from humid to arid conditions in central and western african climate aridification of central africa around 2 8 ma is not clearly recorded at site 959 however decreased and highly fluctuating carbonate carbon concentrations are observed from 2 85 ma on that may relate to enhanced terrigenous eolian dilution from africa

on the duration of the paleocene eocene thermal maximum petm 1 the paleocene eocene thermal maximum petm is one of the best known examples of a transient climate perturbation associated with a brief but intense interval of global warming and a massive perturbation of the global carbon cycle from injection of isotopically light carbon into the ocean atmosphere system one key to quantifying the mass of carbon released identifying the source s and understanding the ultimate fate of this carbon is to develop high resolution age models two independent strategies have been employed cycle stratigraphy and analysis of extraterrestrial helium heet both of which were first tested on ocean drilling program odp site 690 these two methods are in agreement for the onset of the petm and initial recovery or the clay layer main body but seem to differ in the final recovery phase of the event above the clay layer where the carbonate contents rise and carbon isotope values return toward background values here we present a state of the art age model for the petm derived from a new orbital chronology developed with cycle stratigraphic records from sites drilled during odp leg 208 walvis ridge southeastern atlantic integrated with published records from site 690 weddell sea southern ocean odp leg 113 during leg 208 five paleocene eocene p e boundary sections sites 1262 to 1267 were recovered in multiple holes over a depth transect of more than 2200 m at the walvis ridge yielding the first stratigraphically complete p e deep sea sequence with moderate to relatively high sedimentation rates 1 to 3 cm ka where a is years a detailed chronology was developed with nondestructive x ray fluorescence xrf core scanning records on the scale of precession cycles with a total duration of the petm now estimated to be 170 ka the revised cycle stratigraphic record confirms original estimates for the duration of the onset and initial recovery but suggests a new duration for the final recovery that is intermediate to the previous estimates by cycle stratigraphy and heet

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

cave development in the swabian alb south west germany a numerical perspective summary the formation of phreatic cave conduits in the carbonate aquifer of the swabian alb south west germany is discussed by means of numerical simulations three active cave conduit systems the blautopf cave the aachtopf cave and the wimsener cave have been partially explored by divers and exhibit a continuous conduit flow path with phreatic loops down to 50 m below the average water table these three systems drain catchments between 50 and 280 km2 and largely follow the dip of the jurassic limestone beds we use the numerical model karst karst aquifer simulation tool to explore the possibility of structural control of the conduit evolution we show that both the dip of the bedding and the frequency of major bedding partings is likely to result in numerical drainage paths which are similar to the observed cave systems

on the duration of magnetochrons c24r and c25n and the timing of early eocene global warming events implications from the ocean drilling program leg 208 walvis ridge depth transect 1 five sections drilled in multiple holes over a depth transect of more than 2200 m at the walvis ridge se atlantic during ocean drilling program odp leg 208 resulted in the first complete early paleogene deep sea record here we present high resolution stratigraphic records spanning a 4 3 million yearlong interval of the late paleocene to early eocene this interval includes the paleocene eocene thermal maximum petm as well as the eocene thermal maximum etm 2 event a detailed chronology was developed with nondestructive x ray fluorescence xrf core scanning records and shipboard color data these records were used to refine the shipboard derived spliced composite depth for each site and with a record from odp site 1051 were then used to establish a continuous time series over this interval extensive spectral analysis reveals that the early paleogene sedimentary cyclicity is dominated by precession modulated by the short 100 kyr and long 405 kyr eccentricity cycles counting of precession related cycles at multiple sites results in revised estimates for the duration of magnetochrons c24r and c25n direct comparison between the amplitude modulation of the precession component derived from xrf data and recent models of earth s orbital eccentricity suggests that the onset of the petm and etm2 are related to a 100 kyr eccentricity maximum both events are approximately a quarter of a period offset from a maximum in the 405 kyr eccentricity cycle with the major difference that the petm is lagging and etm2 is leading a 405 kyr eccentricity maximum absolute age estimates for the petm etm2 and the magnetochron boundaries that are consistent with recalibrated radiometric ages and recent models of earth s orbital eccentricity cannot be precisely determined at present because of too large uncertainties in these methods nevertheless we provide two possible tuning options which demonstrate the potential for the development of a cyclostratigraphic framework based on the stable 405 kyr eccentricity cycle for the entire paleogene

increased seasonality during the intensification of northern hemisphere glaciation at the pliocene pleistocene boundary 2 6 ma abstract near the pliocene pleistocene neogene quaternary boundary during marine isotope stage mis 104 at around 2 6 ma the intensification of northern hemisphere glaciation inhg was marked by a southward shift of the north atlantic current and arctic front and a concurrent drop in sea surface temperature sst in the mid latitudes of the north atlantic here we evaluate two mg ca based sea surface temperature reconstructions for the 2 78 2 52 ma interval using the planktonic foraminifera globigerina bulloides and globigerinoides ruber white sensu stricto as the biotic carriers sstbul and sstrub and a reconstruction based on the alkenone saturation index sstalk the mg ca based sst estimates begin to diverge from one another significantly during mis g3 2 66 ma culminating during mis 104 2 60 ma and remaining distinctly different for the remaining 80 kyr of the studied interval the magnitude of this divergence sstrub bul is caused mainly by a decrease in sstbul with sstrub remaining relatively constant we attribute this difference to a drop in sst during the early spring blooming season of g bulloides that was less pronounced during the late summer blooming season of g ruber using sstrub bul as a seasonality indicator we show that seasonality increased significantly owing to a drop in early spring temperatures from mis 104 onwards and peaked during glacial episodes maximum seasonality occurred during mis 104 in coincidence with a major expansion of the circum atlantic ice sheets particularly the north american ice sheet this expansion appears to have had a critical influence on global climate and especially seasonality

the messinian salinity crisis past and future of a great challenge for marine sciences forty years after the image of the mediterranean transformed into a giant salty lake was first conceived the fascinating history of the messinian salinity crisis msc still arouses great interest across a large and diverse scientific community early outcrop studies which identified severe palaeoenvironmental changes affecting the circum mediterranean at the end of the miocene were followed by investigations of the marine geology during the 1950s to 1970s these were fundamental to understanding the true scale and importance of the messinian event now after a long period of debate over several entrenched but largely untested hypotheses a unifying stratigraphic framework of msc events has been constructed this scenario is derived mainly from onshore data and observations but incorporates different perspectives for the offshore and provides hypotheses that can be tested by drilling the deep mediterranean basins the msc was an ecological crisis induced by a powerful combination of geodynamic and climatic drivers which had a great impact on the subsequent geological history of the mediterranean area and on the salinity of the global oceans these changed the mediterranean s connections with both the atlantic ocean and the freshwater paratethyan basins causing high amplitude fluctuations in the hydrology of the mediterranean the msc developed in three main stages each of them characterized by different palaeoenvironmental conditions during the first stage evaporites precipitated in shallow sub basins the msc peaked in the second stage when evaporite precipitation shifted to the deepest depocentres and the third stage was characterized by large scale environmental fluctuations in a mediterranean transformed into a brackish water lake the very high resolution timescale available for some late miocene intervals in the mediterranean makes it possible to consider environmental variability on extremely short time scales including in some places annual changes despite this fundamental questions remain some of which could be answered through new cores from the deepest mediterranean basins improvements in seismic imaging and drilling techniques over the last few decades make it possible to plan to core the entire basinal messinian succession for the first time the resulting data would allow us to decipher the causes of this extreme environmental change and its global scale consequences

link between oceanic heat transport thermohaline circulation and the intertropical convergence zone in the early pliocene atlantic planktonic foraminiferal oxygen isotope records from the western and eastern tropical pacific and atlantic oceans suggest a southward shift in the intertropical convergence zone toward its modern location between 4 4 and 4 3 ma a concomitant shift in the carbon isotope compositions of atlantic benthic foraminifera provides strong evidence for an increased thermohaline overturn at this time we suggest that the southward shift of the intertropical convergence zone and associated change in trade wind circulation altered equatorial surface hydrography increased the advection of warmer and more saline surface waters into the subtropical and north atlantic and contributed to thermohaline overturn

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

after the deluge mediterranean stagnation and sapropel formation in an east mediterranean marine core the upper sapropel begins soon after the start of a global event a very heavy precipitation which occurred in the equatorial latitudes during the late glacial early holocene this heavy precipitation in africa channelled by the nile river across 35 of latitude produced a low salinity surface layer in the east mediterranean in this confined basin with high bottom salinity the steep salinity gradient stratified the water column the stagnant bottom waters triggered the sapropel formation cretaceous sapropels in the tropical oceans may result from the same chain of events in warm humid climates with contrasting wet and dry seasonal rhythm

a numerical study of the climate response to lowered mediterranean sea level during the messinian salinity crisis abstract roughly six million years ago tectonic movements isolated the mediterranean sea ms from the atlantic ocean an event known as the messinian salinity crisis msc subsequent evaporative drawdown of the ms resulted in a subaerial depression with a depth between 1500 and 2500 m in this study five simulations are run using the national center for atmospheric research ncar community atmosphere model version 3 cam3 configured with the slab ocean model three simulations have been performed to test the climate impacts to desiccation and to changing the ms base level in this study the ms base level is reduced 750 m in the half land simulation hl and 1500 m in the lowered sea ls and lowered land ll simulations the hl and ll simulations differ from the ls in that the surface is converted to land representing the complete desiccation of the ms the substantial ms depression generates planetary scale atmospheric waves responsible for significant climate effects throughout the northern hemisphere a notable deepening of the aleutian low and a significant equatorward shift in the atlantic jet stream are evident in djf vertical ascent at the northern margin of the ms results in a 1 5 2 5 mm day 1 precipitation anomaly in the ls run over the alps consistent with proxy data annual mean area averaged ms evaporation is slightly higher than control conditions except when salinity is a substantial barrier to evaporation our results suggest that a partially filled basin cannot exist in equilibrium and the ms must either be partly connected to the atlantic ocean or completely desiccated base level lowering which alters the water budget must be taken into account when considering the freshwater budget during the msc

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

response of the african monsoon to orbital forcing and ocean feedbacks in the middle holocene simulations with a climate model that asynchronously couples the atmosphere and the ocean showed that the increased amplitude of the seasonal cycle of insolation in the northern hemisphere 6000 years ago could have increased tropical atlantic sea surface temperatures in late summer the simulated increase in sea surface temperature and associated changes in atmospheric circulation enhanced the summer monsoon precipitation of northern africa by more than 25 percent compared with the middle holocene simulation with prescribed modern sea surface temperatures and provided better agreement with paleorecords of enhanced monsoons

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

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

age refinement of the messinian salinity crisis onset in the mediterranean we propose a revised age calibration of the messinian salinity crisis onset in the mediterranean at 5 971 ma based on the recognition of an extra gypsum cycle in the transitional interval of the perales section sorbas basin spain and the revision of the magnetostratigraphy of the monticino section vena del gesso basin italy this age re calibration allows to state more accurately that i the interval encompassing the msc onset is continuous thus ruling out any erosional feature or stratigraphic hiatus related to a major sea level fall affecting the mediterranean ii the first gypsum was deposited during the summer insolation peak at 5 969 ma associated with an eccentricity minimum and roughly coincident with glacial stage tg32 iii the msc onset was preconditioned by the tectonically driven reduction of the hydrological exchanges with the atlantic ocean and finally triggered by glacial conditions in the northern hemisphere and by arid conditions in northern africa

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

muddled or mixed inferring palaeoclimate from size distributions of deep sea clastics abstract one of the outstanding problems of palaeoclimate reconstruction from physico chemical properties of terrigenous deep sea sediments stems from the fact that most basin fills are mixtures of sediment populations derived from different sources and transported to the site of deposition by different mechanisms conventional approaches to palaeoclimate reconstruction from deep sea sediments do not distinguish between provenance and dispersal related variations and therefore often fail to recognise the true significance of variations in sediment properties we formulate a set of requirements that each proposed palaeo environmental indicator should fulfil and focus on the intrinsic coupling between grain size and chemical composition a critical review of past achievements in grain size analysis serves to introduce a conceptual model of spatio temporal grain size variation based on dynamic populations each dynamic population results from a characteristic combination of production and transport mechanisms that corresponds to a distinct subpopulation in the data analysed the mathematical statistical representation of the conceptual model can be obtained by means of the end member modelling algorithm emma applications of the model to several ocean basins are discussed as well as methods to examine the validity of grain size based palaeoclimate reconstructions palaeoclimate reconstructions of a high and low latitude basin illustrate the common degree of complexity of deep sea grain size records

relative importance of meridional and zonal sea surface temperature gradients for the onset of the ice ages and pliocene pleistocene climate evolution received 12 june 2009 revised 22 december 2009 accepted 13 january 2010 published 23 june 2010 1 during the early pliocene roughly 4 myr ago the ocean warm water pool extended over most of the tropics subsequently the warm pool gradually contracted toward the equator while midlatitudes and subpolar regions cooled establishing a meridional sea surface temperature sst gradient comparable to the modern about 2 myr ago as estimated on the eastern side of the pacific the zonal sst gradient along the equator virtually nonexistent in the early pliocene reached modern values between 1 and 2 myr ago here we use an atmospheric general circulation model to investigate the relative roles of the changes in the meridional and zonal temperature gradients for the onset of glacial cycles and for pliocene pleistocene climate evolution in general we show that the increase in the meridional sst gradient reduces air temperature and increases snowfall over most of north america both factors favorable to ice sheet inception the impacts of changes in the zonal gradient while also important over north america are somewhat weaker than those caused by meridional temperature variations the establishment of the modern meridional and zonal sst distributions leads to roughly 3 2 c and 0 6 c decreases in global mean temperature respectively changes in the two gradients also have large regional consequences including aridification of africa both gradients and strengthening of the indian monsoon zonal gradient ultimately this study suggests that the growth of northern hemisphere ice sheets is a result of the global cooling of earth s climate since 4 myr rather than its initial cause thus reproducing the correct changes in the sst distribution is critical for a model to simulate the transition from the warm early pliocene to a colder pleistocene climate

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

provenance of present day eolian dust collected off nw africa 1 atmospheric dust samples collected along a transect off the west african coast have been investigated for their physical grain size distribution mineralogical and chemical major elements composition on the basis of these data the samples were grouped into sets of samples that most likely originated from the same source area in addition shipboard collected atmospheric meteorological data modeled 4 day back trajectories for each sampling day and location and total ozone mapping spectrometer aerosol index data for the time period of dust collection february march 1998 were combined and used to reconstruct the sources of the groups of dust samples on the basis of these data we were able to determine the provenance of the various dust samples it appears that the bulk of the wind blown sediments that are deposited in the proximal equatorial atlantic ocean are transported in the lower level 900 hpa ne trade wind layer which is a very dominant feature north of the intertropical convergence zone itcz however south of the surface expression of the itcz down to 5 s where surface winds are southwesterly we still collected sediments that originated from the north and east carried there by the ne trade wind layer as well as by easterly winds from higher altitudes the fact that the size of the wind blown dust depends not only on the wind strength of the transporting agent but also on the distance to the source hampers a direct comparison of the dust s size distributions and measured wind strengths however a comparison between eolian dust and terrigenous sediments collected in three submarine sediment traps off the west coast of nw africa shows that knowledge of the composition of eolian dust is a prerequisite for the interpretation of paleorecords obtained from sediment cores in the equatorial atlantic

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

southern ocean dust climate coupling over the past four million years dust plays a central part in ocean biogeochemical cycles by supplying iron and other essential micronutrients to regions where marine productivity is limited by the availability of iron martinez garcia et al present a marine record of dust and iron supply to the southern ocean during the past four million years the data derived from leaf waxes establish that previous records of dust flux from antarctic ice cores are broadly representative of a larger area importantly the dust and iron supply rose sharply 1 25 million years ago suggesting that increased dust supply may be a major influence on the more severe swings between the glacial and interglacial climate of the late pleistocene dust has the potential to modify global climate by influencing the radiative balance of the atmosphere and by supplying iron and other essential limiting micronutrients to the ocean1 2 indeed dust supply to the southern ocean increases during ice ages and iron fertilization of the subantarctic zone may have contributed up to 40 parts per million by volume p p m v of the decrease 80 100 p p m v in atmospheric carbon dioxide observed during late pleistocene glacial cycles3 4 5 6 7 so far however the magnitude of southern ocean dust deposition in earlier times and its role in the development and evolution of pleistocene glacial cycles have remained unclear here we report a high resolution record of dust and iron supply to the southern ocean over the past four million years derived from the analysis of marine sediments from odp site 1090 located in the atlantic sector of the subantarctic zone the close correspondence of our dust and iron deposition records with antarctic ice core reconstructions of dust flux covering the past 800 000 years refs 8 9 indicates that both of these archives record large scale deposition changes that should apply to most of the southern ocean validating previous interpretations of the ice core data the extension of the record beyond the interval covered by the antarctic ice cores reveals that in contrast to the relatively gradual intensification of glacial cycles over the past three million years southern ocean dust and iron flux rose sharply at the mid pleistocene climatic transition around 1 25 million years ago this finding complements previous observations over late pleistocene glacial cycles5 8 9 providing new evidence of a tight connection between high dust input to the southern ocean and the emergence of the deep glaciations that characterize the past one million years of earth history