a 300 kyr high resolution aridity record of the north african continent new oxygen isotope data and a high resolution carbonate record of a core from the northwest african margin are presented in combination with geochemical zr rb ratio al ba organic carbon and biogenic opal fluxes and sedimentological median grain size parameters to show variations in african continental aridity wind strength and upwelling productivity the carbonate record is diluted by the supply of aeolian dust from the arid saharan region of north africa and is seen to vary with a characteristic sawtooth pattern indicating rapid increases in dust flux followed by gradual declines spectral analysis of the carbonate profile and comparison with specmap stacked oxygen isotope and etp solar radiation profiles shows that the precessional 23 kyr insolation induced african climate system is decoupled from global ice volume climate changes operating on a 100 kyr frequency detailed studies of glacial terminations i ii and iii confirm the presence of rapid short timescale climatic variations in aridity

the late pleistocene palaeoclimatic record of north atlantic deep sea sediments revealed by mineral magnetic measurements eight cores of north atlantic deep sea sediment are correlated using simple rapid and non destructive measurements of magnetic susceptibility and isothermal remanence this stratigraphy is demonstrably related to late pleistocene palaeoclimatic variations by comparison with the oxygen isotope and microfossil records of these cores fluctuations in the concentration dependent magnetic properties of the cores largely reflect their lithological composition consisting of climatically modulated cycles of marl glacial horizons and nannofossil chalk interglacial horizons high magnetic concentration characterises glacial horizons which correspond to periods when carbonate productivity was severely restricted and ice rafted detrital inputs were prolific coincident with the migration south of the north atlantic polar front to within 3 of latitude north of the coring site in contrast interglacial horizons are characterised by low magnetic concentration and high carbonate content of the sediment consequent on the retreat of the polar front and the re establishment of coccolith floras in its wake during these periods ratios formed between individual magnetic parameters are independent of magnetic concentration and are thus free of any climatic influences wrought by carbonate oscillations in this study however such ratios exhibit a definite response to palaeoclimatic variations attributable to differences in the composition and grain size of the magnetic mineral assemblage of glacial vis a vis interglacial horizons of the cores these differences in mineral magnetic composition are substantially confirmed by mossbauer effect studies of selected samples representing peak glacial and interglacial horizons of one core such glacial interglacial contrasts in the concentration mineralogy and grain size of the magnetic assemblage most probably result from variations in the source and flux density of detritral inputs induced by changes in climate x ray diffraction studies of the same core indicate that variations in the mineralogy of the detrital fraction of the sediment are consistent with those of the magnetic assemblage together these data point to the conclusion that a subsidiary low latitude possibly aeolian detrital flux supplements high latitude ice rafted input in glacial horizons of the cores the low latitude flux however is also identifiable in interglacial horizons independent evidence suggests that this low latitude aeolian flux may be derived from the sahel region of north africa and transported to the coring site by harmattan winds associated with saharan dust outbreaks

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

abrupt environmental oscillations during the early weichselian recorded at lago grande di monticchio southern italy abstract this study presents multi proxy data from a new core from lago grande di monticchio italy extending back to about 100 000 calendar years bp the time scale of this record is independent from deep sea and ice core chronologies and has been established from a combination of varve counts and high resolution sedimentation rate calculations based on microscopic sediment investigation this paper focuses on environmental variability between 100 000 and 65 000 calendar years bp several abrupt cold periods have been recognised and correlated to other terrestrial as well as to ice core and deep sea records the longest of the monticchio cold phases corresponds to marine isotopic stage 5b and lasted from ca 87 000 to 84 000 calendar years bp two shorter events about 1000 years long occurred during the transition from interstadial to full glacial conditions between 79 000 and 75 000 calendar years bp the increased frequency of cold events during this time interval probably indicates a higher degree of climatic instability in periods of major changes dating discrepancies between monticchio grip and deep sea chronologies range between a few hundred to a few thousand years however these differences in dating are not constant but vary significantly for different sections of the records nevertheless the good match of environmental fluctuations at monticchio with atmospheric variability at the greenland summit as well as variations in the oceanic circulation pattern suggests a close link of the mediterranean to the atlantic climate regime

hydrological relationship between the north atlantic ocean and the mediterranean sea during the past 15 75 kyr the mediterranean sea hydrology at the time of the heinrich formation in the north atlantic ocean was analyzed by comparing sea surface temperatures ssts and oxygen isotope composition of seawater w changes during the past 75 kyr in two marine cores these were compared to the palynological variations derived in the mediterranean sea core during the last glacial the two oceanic sst records show similar and synchronous patterns with several long term cooling periods ending by abrupt sst increases at the time of the heinrich events cold ssts and low salinity prevailed in the mediterranean sea the freshwater budget was similar to the modern one permitting the presence of a mixed forest on the mediterranean borderlands the post heinrich periods are marked by a freshwater budget decrease limiting oak and fir tree growth in the mediterranean region increase of precipitation or reduction of evaporation is observed before the heinrich episode and is associated with a well developed mixed mediterranean forest

late quaternary western mediterranean pollen records and african winds abstract late quaternary vegetation changes of regional and global significance in the mediterranean region are generally interpreted as being controlled by changes in the circulation patterns of north atlantic air masses however the possibility cannot be excluded that they may also be related to winds blowing from africa long pollen records from southwest europe show that cedrus pollen of northwest african provenance is found during the glacial periods and occasionally during abrupt deforestation events in the forest dominated periods of the interglacials a pollen concentration record from central italy shows that during the holocene the presence of cedrus pollen coincides with two abrupt deforestation events around 8 1 and 4 2 cal kyr bp these observations raise the question of a possible influence of eolian activity on arboreal vegetation during phases of climatic stress towards aridity and suggest the use of modern pollen monitoring as a strategy for revealing tendencies towards aridification in southwestern europe

palaeoclimatic cyclicity in central mediterranean pliocene sediments the mineralogical signal abstract a high resolution x ray mineralogical study of four pliocene sediment sections from the central mediterranean punta piccola sicily monte singa and vrica calabria odp hole 964 a ionian sea shows cyclic opposite abundance variations of two groups of clay minerals the first is dominated by palygorskite and kaolinite whose abundance maxima can be interpreted as resulting from periods of aridity on the african continent allowing their transport as wind blown dust the second is dominated by smectite whose abundance maxima can be interpreted as indicative of periods of abundant rainfall on the mediterranean borderlands these variations in abundance show a 22 ky cyclicity implying a control by the precession of the earth s orbit sapropels and sapropelic layers always occur in the smectite rich beds and therefore appear to have been deposited during the wet periods

rapid environmental changes in southern europe during the last glacial period oxygen isotope records from greenland ice cores1 2 indicate numerous rapid climate fluctuations during the last glacial period north atlantic marine sediment cores show comparable variability in sea surface temperature and the deposition of ice rafted debris3 4 5 in contrast very few continental records of this time period provide the temporal resolution and environmental sensitivity necessary to reveal the extent and effects of these environmental fluctuations on the continents here we present high resolution geochemical physical and pollen data from lake sediments in italy and from a mediterranean sediment core linked by a common tephrochronology our lacustrine sequence extends to the past 102 000 years many of its features correlate well with the greenland ice core records demonstrating that the closely coupled ocean atmosphere system of the northern hemisphere during the last glacial4 extended its influence at least as far as the central mediterranean region numerous vegetation changes were rapid frequently occurring in less than 200 years showing that the terrestrial biosphere participated fully in last glacial climate variability earlier than 65 000 years ago our record shows more climate fluctuations than are apparent in the greenland ice cores together the multi proxy data from the continental and marine records reveal differences in the seasonal character of climate during successive interstadials and provide a step towards determining the underlying mechanisms of the centennial millennial scale variability

abrupt cold spells in the northwest mediterranean hitherto unknown abundance peaks of left coiling l c neogloboquadrina pachyderma from a gulf of lions piston core indicate that abrupt cold spells associated with atlantic heinrich events affected the mediterranean n pachyderma l c is typical of sub polar waters in the open ocean the southern edge of its glacial north atlantic bioprovince reached south portugal only trace abundances of n pachyderma l c are known from quaternary mediterranean sediments suggesting that no significant invasions occured via the strait of gibraltar the gulf of lions abundance peaks therefore seem to reflect area specific thriving of a normally rare but indigenous taxon in the western mediterranean through local favorable habitat development the general planktonic foraminiferal record suggests that the basic hydrographic regime in the gulf of lions with wintertime deep convective overturn was relatively stable over the past 60 kyr under these conditions high abundances of n pachyderma l c would essentially imply temperature reductions of the order of 5 8 relative to the present

longitudinal spreading of granular flow in trapezoidal channels abstract debris flows have a long runout distance and can result in devastating consequences the mobility of debris flows are influenced by their rheological behavior and the topography of their flow path trapezoidal cross sectional channels can more accurately model channelized topography and yield more accurate mobility analyses however the flow mechanisms influencing mobility in trapezoidal channels are not well understood a 5 m long uniform trapezoidal flume with adjustable sidewall angles is used to investigate the mobility of dry granular surge flows experimental tests are conducted for sidewall angles of 30 45 and 90 numerical back analysis using the discrete element method dem is subsequently conducted to interpret the flume experiments furthermore a new dimensionless group 1 is presented to characterize the flow mechanism of longitudinal spreading experimental and numerical results both reveal that increasing sidewall angles reduce flow mobility steep sidewalls increase flow depths which promotes longitudinal spreading longitudinal spreading is responsible for attenuating the flow mass and reducing mobility the dimensionless group 1 shows to be an appropriate indicator for characterizing the longitudinal spreading mechanism of a flow mass the consideration of longitudinal spreading and channel sidewall angle is demonstrated to be necessary for a comprehensive mobility assessment

weichselian palynological records from southern europe correlation and chronology abstract the high resolution independently dated palynostratigraphic record from lago grande di monticchio spanning the last 101 530 calendar years provides a basis for re evaluating the correlations between palaeoenvironmental events in europe during the last glacial as well as a means to determine their chronology the interstadial events recorded from various localities throughout europe are combined into a single scheme of correlations and a chronological framework is suggested this provides a basis for assessing the evolution of the vegetation and environmental patterns across europe during the last glacial revealing a general tendency for the latitudinal climatic gradient to have been steeper than it has been during the holocene the vegetation has also generally been subject to greater moisture deficiency either because of prevailing climatic conditions or as a reflection of the lower atmospheric concentration of co 2 the scheme of correlations is shown to be capable of being extended beyond europe not only to marine and ice core records from the north atlantic region but also to a palynological record from north west north america

interbasin deep water exchange in the western mediterranean owing to its nearly enclosed nature the tyrrhenian sea at first sight is expected to have a small impact on the distribution and characteristics of water masses in the other basins of the western mediterranean the first evidence that the tyrrhenian sea might in fact play an important role in the deep and intermediate water circulation of the entire western mediterranean was put forward by hopkins 1988 there an outflow of water from the tyrrhenian sea into the algero provencal basin was postulated in the depth range 700 1000 m to compensate for an observed inflow of deeper water into the tyrrhenian sea however this outflow the tyrrhenian deep water tdw was undetectable since it would have hydrographic characteristics that could also be produced within the algero provencal basin a new data set of hydrographic tracer lowered acoustic doppler current profiler ladcp and deep float observations presented here allows us now to identify and track the tdw in the algero provencal basin and to demonstrate the presence and huge extent of this water mass throughout the western mediterranean it extends from 600 m to 1600 1900 m depth and thus occupies much of the deep water regime the outflow from the tyrrhenian is estimated to be of the order of 0 4 sv sv 10 6 m 3 s 1 based on the tracer balances this transport has the same order of magnitude as the deep water formation rate in the gulf of lions the tyrrhenian sea effectively removes convectively generated deep water western mediterranean deep water wmdw from the algero provencal basin mixes it with levantine intermediate water liw above and reinjects the product into the algero provencal basin at a level between the wmdw and liw thus smoothing the temperature and salinity gradients between these water masses the tracer characteristics of the tdw and the lowered adcp and deep float observations document the expected but weak cyclonic circulation and larger flows in a vigorous eddy regime in the basin interior

evidence for a change in the periodicity of tropical climate cycles at 2 4 myr from whole core magnetic susceptibility measurements the earth s orbit about the sun is influenced by gravitational interactions with the moon and other planets the resulting orbital perturbations give rise to cyclical variations in orbital eccentricity obliquity and precession with periods of 100 41 19 and 23 kyr respectively1 these variations are climatically important because they affect the seasonal and latitudinal distribution of solar radiation magnetic susceptibility measurements in deep sea sediment cores can be used as a sensitive indicator of temporal variations in the concentration of terrigenous material supplied to the sea bed here we use this approach to study the evolution of cycles of terrigenous sedimentation at ocean drilling program sites in the arabian sea and the eastern tropical atlantic we show from spectral analyses of the two susceptibility time series spanning the past 3 2 3 5 myr that the records are driven strongly by orbital forcing before 2 4 myr before present bp both records are strongly influenced by the 23 and 19 kyr periodicities but after 2 4 myr they are both significantly influenced by the 41 kyr periodicity this shift coincides with the beginning of major northern hemisphere glaciation which indicates for the indian ocean site that the supply of terrigenous sediment carried by monsoonal winds has responded to the rapid increase in ice cover at this time we cannot however exclude possible effects of changes in bottom water circulation on the susceptibility record of the atlantic site

the last 100 000 years in the western mediterranean sea surface water and frontal dynamics as revealed by coccolithophores a quantitative analysis was carried out on coccolith assemblages from two pleistocene cores k1 and k10 from the western mediterranean the distribution of selected coccolithophore species provides new paleoclimatic and paleoceano graphic data a continuous sequence from the top of isotope stage 5 to the holocene was recorded the reversal in dominance between gephyrocapsa muellerae and emiliania huxleyi was dated in both cores at ca 73 ka at about 47 ka e huxleyi shows a regular increase whereas g muellerae progressively decreases in abundance during interglacial periods high concentrations of coccoliths are observed whereas in glacial times coccoliths are more diluted and the percentage of reworked forms increases as a consequence of the higher terrigenous input after taking careful account of the dilution factor we conclude that the production of coccolithophores was higher during warm periods maxima in coccolith concentrations coincide with highstand episodes probably as a result of the intensification of the atlantic flux into the mediterranean across the gibraltar strait this intensification could have produced an increase in nutrient content in the surface mediterranean waters during cold periods the western mediterranean front underwent a reduction in activity probably due to an increase in the saline and or thermal gradients between the superficial waters and intermediate waters in the liguro provencal basin

synchroneity between marine and terrestrial responses to millennial scale climatic variability during the last glacial period in the mediterranean region land sea climatic proxies have been obtained from the last glacial section of images core md95 2043 western mediterranean sea vegetation and alkenone derived sst curves indicate rapid 150 years and synchronous terrestrial and marine climatic changes paralleling the dansgaard oeschger d o climatic variability over greenland this frequency of climate change can be related to shifts between the two modes of operation of the north atlantic oscillation nao transfer functions applied to the pollen data indicate that there was an amplification of the climatic signal during heinrich events hes in comparison with other d o stadials the development and persistence of both scandinavian and atlantic mobile polar highs over southwestern europe may explain the extreme cooling 10 c and dryness 400 mm during heinrich events 5 and 4 in the mediterranean region comparison of the results of core md95 2043 with similar climatic data from images core md95 2042 located off portugal indicates that thermal and precipitation gradients occurred between the mediterranean and the atlantic sides of iberia within hes hes 4 and 5 are associated with more humid conditions in the atlantic by 200 mm than in the mediterranean site as is the case at the present time this comparison also illustrates the different behaviour of these areas during the d o stadials in contrast with the mediterranean site the atlantic site shows similar precipitation and temperature drops for all the d o stadials including those related to the hes here we propose the operation of different mobile polar highs mph as the driving mechanism for this difference in behaviour between the atlantic and mediterranean sides of iberia hes are related to a stronger influence of the scandinavian mph forcing a severe aridification and cooling of the full iberian peninsula the atlantic mph may have been dominant during the other stadials which would preferentially affect southwestern iberia

global ice volume fluctuations north atlantic ice rafting events and deep ocean circulation changes between 130 and 70 ka multiproxy data from north atlantic deep sea sediment core neap18k provide a detailed record of climate through oxygen isotope stage ois 5 seven distinct large scale episodes of ice rafting c25 c19 were identified between 126 and 70 ka global ice volume reconstructions based on high resolution benthic 18 o records indicate that major ice rafting events were not confined to ice volume maxima at ois 5d and 5b but also occurred during periods of ice sheet growth and disintegration however iceberg discharges were restricted to times when sea levels were 40 65 m below present values ice rafting episode c25 the first large scale cooling of mid atlantic surface waters after the last interglacial occurred during the gradual buildup of continental ice sheets at the ois 5e 5d transition major ice sheet collapses allied to ice rafting events c24 and c21 were associated with rapid sea level increases of 20 and 40 m respectively suborbital climatic fluctuations in the neap18k sedimentary record denoted by prominent 7 5 4 5 and 3 k y cyclicities appear to correlate with both greenland atmospheric temperatures and changes in thermohaline circulation patterns inferred from benthic 13 c values and hence provide clear evidence of a highly interconnected north atlantic climatic regime during ois 5

sedimentary mechanisms and underlying tectonic structures of the northwestern mediterranean margin as revealed by comprehensive bathymetric and seismic surveys abstract the tectonic structures lithological contrasts and sedimentary processes of the northwestern mediterranean margin are revealed by a comprehensive survey including recently acquired seabeam and seismic profiling data mass wasting by gravity flow processes occurs over this entire area gravity slides are concentrated on the thick plio quaternary formations located in the interchannel areas they can lead to surprisingly steep walls and contribute to the widening of the canyons the contrasts between these superficial formations and the underlying neogene formations are morphologically well expressed the slide products sometimes directly observed as voluminous erratic blocks can seal the deep sea channels and cause their migrations areal extent of these slides can be very large especially with respect to the small size of the basin however the turbidity currents are the main gravity flow processes leading to the construction during the quaternary glacial epochs of the rhone deep sea fan and other sedimentary ridges they are responsible for the formation of particular bedforms such as circular depressions into the valley floors or sediment waves on the interchannel areas the wide extent of the gravity flow processes can be explained by the particular geological setting of this margin which is a mountainous borderland with steep slopes and rapid deposition of undercompacted sediments the general instability is favored by recent tectonic movements linked with the alpine setting and especially in the deepest areas by the lubricating effects of the underlying messinian salt layer under the loading effect of the sedimentary cover this salt layer crops out around the rhone deep sea fan as a peripheral belt of diapirs having shapes controlled by deep tectonic structures

the late oligocene cevizlidere cu au mo deposit tunceli province eastern turkey the cevizlidere deposit located in the tunceli province of eastern anatolia is the largest porphyry cu au mo system in turkey the deposit is spatially related to a composite stock which was emplaced into paleozoic limestones and paleogene andesitic rocks to the southeast of the munzur mountains near the southwestern margin of the ovacik pull apart basin the host plutonic rocks at cevizlidere are porphyritic medium k calc alkaline diorites and granodiorites 40ar 39ar incremental step heating analysis of two igneous biotite separates obtained from syn mineral diorite porphyry yielded late oligocene cooling ages of 25 49 0 10 and 25 10 0 14 ma whereas hydrothermal biotite yielded an age of 24 73 0 08 ma re os ages obtained from two molybdenite separates 24 90 0 10 and 24 78 0 10 ma indicate that porphyry style alteration and mineralization developed shortly after magma emplacement the whole rock geochemical composition of the cevizlidere porphyry intrusions is consistent with derivation from partial melting of the metasomatized supra subduction zone mantle however based on regional tectonic reconstructions oligocene magmatic activity in this area appears to be related to a major kinematic reorganization that took place at around 25 ma during the switch from subduction to collisional tectonics in eastern anatolia this kinematic switch may be attributed to break off of the southern neo tethys oceanic slab prior to the arabia eurasia continent continent collision 12 10 ma following widespread middle eocene 50 43 ma arc back arc magmatism in this respect the subduction related tectonic setting of the late oligocene cevizlidere porphyry deposit is similar to that of the middle eocene copler epithermal au deposit the late timing of cevizlidere with respect to the southern neo tethys subduction may be comparable to some early to late miocene porphyry epithermal systems that lie within the contiguous urumieh dokhtar belt in central iran the later timing in iran reflects the diachronous nature of the eurasia afro arabia collision

late quaternary sedimentation patterns of the ebro turbidite systems northwestern mediterranean two styles of deep sea deposition abstract seven sediment types are identified from the analysis of 60 piston cores in the ebro turbidite systems 1200 1800 m deep between the ebro shelf and the valencia trough in the northwestern mediterranean sea these sediments are grouped into five facies associations channel floor of erosive depositional channel levee complex levee of erosive depositional channel levee complex depositional channel levee complex interchannel and apron facies unconfined slides debris flows channeled turbidity currents and differential hemipelagic settling are the main depositional processes which develop these facies deposition in the ebro turbidite systems occurred primarily during the pleistocene when turbidity currents funneled coarsegrained sediments through canyon channel systems during the holocene most sediment was trapped in deltaic and nearshore environments and turbidite deposition was replaced by hemipelagic settling in the hemipelagic sequence thus created grain size terrigenous components and chlorite kaolinite and illite kaolinite ratios decrease upwards while planktonic and calcite quartz ratios increase two styles of growth patterns are present during periods of low sea level most common are base of slope channel levee complexes each of which is developed alongside an older complex the complexes were formed by sediment supplied from different canyons as the systems migrated from north to south with time in addition in the central sector base of slope aprons have been formed in gullied slope terrains by unconfined slides and less commonly by unconfined turbidity currents the major differences between the ebro and other base of slope systems are a the incomplete development of channel levee complexes as compared to typical deep sea fans b the coexisting growth of aprons and c multiple canyon sources low slope stability resulting in many sediment supply point sources is one of the primary factors which encourages development of base of slope aprons

variations in terrigenous dilution in western mediterranean sea pelagic sediments in response to climate change during the last glacial cycle hemipelagic intervals in four giant calypso piston cores from the balearic abyssal plain western mediterranean sea were studied in order to determine fluctuations in the supply of terrigenous sediments to the basin during the last 130 000 years and possible climatic modulation of terrigenous sediment and particle flux carbonate records from hemipelagic intervals in these cores display distinct atlantic type cycles where glacial periods show on average 20 lower calcium carbonate contents than interglacial period equivalents the decrease in calcium carbonate seen during glacials may be the result of increased dilution by terrigenous aeolian and fluvial particles derived from aeolian and or fluvial sources higher glacial aeolian particle fluxes to the western mediterranean sea may have been caused by changes in the prevailing atmospheric conditions resulting in drier and colder climatic conditions in the source areas and more frequent and intense outbreaks of dust transport the colder and drier climatic conditions in combination with a lowered sea level would allow rivers to dump their sediment load closer to the shelf edge promoting enhanced fluvial input into the basin besides significant calcium carbonate variations that correlate with glacial interglacial cycles several short term abrupt changes in the calcium carbonate content are recorded which appear coincident with enhanced magnetic susceptibility values especially the events within marine isotope stage mis 3 the timing of these short term events may be linked with cooling events in the north atlantic particularly heinrich events and cold events within mis 5 these short term trends may possibly be explained by increased terrigenous particle transport due to drier and colder climate in the mediterranean borderlands our results further show that about 90 of the sedimentary sequence of the balearic abyssal plain consists of turbidites generally these appear not to have caused significant erosion and an almost complete continuous time stratigraphy is present in the intercalated hemipelagic intervals

low sea level stand emplacement of megaturbidites in the western and eastern mediterranean sea piston cores from the balearic and herodotus abyssal plains in the mediterranean sea show that the late pleistocene to holocene sedimentary sequence is dominated by turbidite muds on each plain one turbidite bed is conspicuous by its thickness and this bed can be correlated basinwide on the basis of geochemical compositional analysis and its apparent correspondence with a distinct acoustically transparent layer on high resolution seismic records these megabeds on the two plains represent megaturbidites of very large volume 300 600 km3 each and are shown by ams radiocarbon dating to have been emplaced during the last low stand of sea level at the height of the last glacial maximum the megabed on the balearic abyssal plain is derived from the southern european margin and is the main sedimentation event over the last 120 ka it emplaced as much material as was deposited by smaller flows during the previous 25 ka sedimentation rate curves for the balearic abyssal plain show that falling sea level correlates with increased terrigenous deposition and that gross sedimentation rates in the basin increased as sea level fell from 120 18 ka due to more frequent emplacement of distal turbidites the herodotus abyssal plain megabed is derived from the libyan egyptian continental shelf west of the nile delta and was the dominant sedimentation event in this basin during the past 60 kyr high resolution seismic profiles from the ionian and sirte abyssal plains in the central mediterranean also suggest possible low sea level emplacement of megabeds in these regions available evidence suggests widespread emplacement of megaturbidites throughout the mediterranean at the last glacial maximum although the triggering mechanisms for these events remain speculative catastrophic destabilisation of the margin after a long period of accumulation with an increased rate of sediment supply is suggested

sea surface temperature during the quaternary at odp sites 976 and 975 western mediterranean abstract based on the relative abundances of the planktonic foraminifera species found in quaternary samples from odp sites 976 alboran sea and 975 menorca rise and using a modern analog technique winter and summer sea surface temperatures were estimated frequency distributions of temperatures are asymmetrical more so at odp site 976 where there is a greater abundance of samples from the warm part of the temperature range during the quaternary there is a general tendency for temperatures to fall with an overall diminution of 1 c for the winters and of more than 2 c for the summers overall mean temperatures and those of the biostratigraphic intervals identified are higher at odp site 975 than at 976 when differences are statistically significant the q1 interval i e the oldest in the quaternary is colder than the upl i e terminal pliocene and the q2 interval the q3 interval is also colder than the q2 interval and the q4 interval i e the most recent interval differences between intervals general trends and the asymmetries of frequency distributions cannot be explained as linear responses to insolation the stratigraphic series from odp site 976 was dated by correlating the relative maxima and minima of the summer temperature series with those of insolation during the month of july at 65 n it was found that 26 2 of the variance of the time series of temperatures was concentrated in the harmonics related to precession and obliquity while 19 was located in those related to eccentricity there are indications of the need to add lags and leads to the age of temperature spikes with respect to insolation but such delays and leads cannot be quantified precisely

magnetic susceptibility variations in upper pleistocene deep sea sediments of the ne atlantic implications for ice rafting and paleocirculation at the last glacial maximum magnetic susceptibility ms variations are used to intercorrelate 17 upper pleistocene sediment cores taken from the ne atlantic between 40 degrees and 60 degrees n the ms based correlation depends on regionally consistent patterns of variation in the deposition of ice rafted detritus ird in response to pleistocene glaciations and especially to high frequency ice rafting episodes referred to in recent studies as heinrich events the sedimentological and rock magnetic basis for the apparent relationship between the ms signal and ird content of ne atlantic sediments is examined by 1 comparing the ms profiles of selected cores with their records of coarse fraction 150 mu m lithic fragment abundance and neogloboquadrina pachyderma sin percentages and 2 normalizing ms by expressing it both on a carbonate free basis and as a quotient with anhysteretic remanent magnetization a parameter sensitive to magnetic mineral grain size variations these comparisons show that variations in bulk sediment ms are only partly driven by simple carbonate dilution productivity and dissolution effects changes in both the concentration and grain size of magnetic minerals within the lithogenic noncarbonate fraction also impose a significant influence on bulk ms values in particular horizons rich in ird are associated with significant increases in the relative proportion of coarse grained multidomain ferrimagnetic particles in the sediment this is because ice rafting in contrast to most other mechanisms capable of transporting detrital magnetic minerals to pelagic environments has a high potential for delivering large ferrimagnetic grains as components of sand sized polycrystalline lithic fragments this fundamental linkage between the ird content and ms signal of ne atlantic sediments is used to reconstruct the patterns of variation in ird deposition and by inference surface currents of the last glacial maximum lgm similar to 18 19 ka relative to the present day ne atlantic using the time slice mapping approach developed by the climap project group our lgm holocene ms ratio map based on sample pairs from over 80 deep sea cores confirms that there was a weak cyclonic gyre north of the polar front in the lgm north atlantic the gyre comprised a sluggish warm current in the ne atlantic flowing north between latitudes 47 degrees and 62 degrees n partly fed by subtropical waters from south of the polar front and carrying large numbers of icebergs derived from several sources most of which melted between latitudes 45 degrees and 52 degrees n the warm current probably continued its flow into the iceland basin where it fed into a south flowing current which transported melting icebergs from iceland and scandinavia along the western flank of the reykjanes ridge

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

three million years of monsoon variability over the northern sahara we present a 3 million year record of aeolian dust supply into the eastern mediterranean sea based on hematite contents derived from magnetic properties of sediments from ocean drilling program site 967 our record has an average temporal resolution of 400 years geochemical data validate this record of hematite content as a proxy for the supply of aeolian dust from the sahara we deduce that the aeolian hematite in eastern mediterranean sediments derives from the eastern algerian libyan and western egyptian lowlands located north of the central saharan watershed 21 n in corroboration of earlier work we relate dust flux minima to penetration of the african summer monsoon front to the north of the central saharan watershed this would have enhanced soil humidity and vegetation cover in the source regions in agreement with results from green sahara climate models our results indicate that this northward monsoon penetration recurred during insolation maxima throughout the last 3 million years as would be expected this orbital precession scale mechanism is modulated on both short 100 kyr and long 400 kyr eccentricity time scales we also observe a strong expression of the 41 kyr obliquity cycle which we discuss in terms of high and low latitude mechanisms that involve southern hemisphere meridional temperature contrasts and shifts in the latitudes of the tropics respectively we also observe a marked increase in sub milankovitch variability around the mid pleistocene transition 0 95 ma which suggests a link between millennial scale climate variability including monsoon dynamics and the size of northern hemisphere ice sheets

environmental magnetism past present and future environmental magnetism involves the application of rock and mineral magnetic techniques to situations in which the transport deposition or transformation of magnetic grains is influenced by environmental processes in the atmosphere hydrosphere and lithosphere the first explicit description of environmental magnetism as a distinct field was in 1980 since that time environmental magnetism has become a broad field that is finding application in an ever increasing array of scientific disciplines in this review of the present state of environmental magnetic studies we divide the field into three broad but arbitrary categories the first involves the use of mineral magnetic assemblages in the geological record to study physical processes in depositional environments this category includes the correlation of sediment cores using magnetic susceptibility measurements studies of geomagnetic field behavior the analysis of depositional and postdepositional mechanical processes that affect sediments and the examination of magnetic parameters that might represent proxies for paleoclimatic variation the second category encompasses studies of the processes responsible for variations in the magnetic minerals brought into a sedimentary environment these provenance investigations include studies of changes in catchment derived sediment in lakes fluctuations in contributions from terrigenous aeolian and glaciogenic components in deep sea sediments and the origin of atmospheric particulates the final category addresses in situ changes and transformations of magnetic minerals in sedimentary environments including pedogenesis authigenetic diagenetic formation of ferrimagnetic phases dissolution of magnetic minerals due to reductive diagenesis and contributions of biomagnetism to sedimentary magnetism because environmental magnetism can address problems in so many disciplines and because many of these problems may be inaccessible to other techniques it is likely that the scope of environmental magnetism will continue to expand rapidly environmental magnetism is capable of providing important data for studies of global environmental change climatic processes and the impact of humans on the environment all of which are major research initiatives in the international scientific community these factors suggest that environmental magnetism has a bright and diverse future

evidence for enhanced mediterranean thermohaline circulation during rapid climatic coolings molecular biomarkers c37 alkenones n nonacosane and n hexacosanol and toc are used together with benthic 18o and 13c data to document the hydrographic response of the western mediterranean sea to rapid climatic variability these proxies are recorded in core md 95 2043 alboran sea affording the study of the dansgaard oeschger d o and heinrich he variability during the last glacial period the results suggest that rapid changes in the western mediterranean thermohaline circulation occurred in parallel to sea surface temperature oscillations enhanced deep water ventilation occurred during cold intervals he and d o stadials probably driven by a strengthening of north westerly wind over the north western mediterranean sea in contrast decreased intensity of the thermohaline circulation is detected during warm intervals d o interstadials which led to low oxygenated deep water masses and better preservation of the organic matter in the sediment

mediterranean vegetation lake levels and palaeoclimate at the last glacial maximum the apparent conflict between pollen evidence for widespread artemisia steppe1 6 implying semi arid conditions and geomorphological evidence for high lake levels4 7 11 has produced controversy about the ice age palaeoclimate of the mediterranean region here we use a water balance model12 to predict catchment runoff and a biome model13 to predict vegetation type to reconstruct the palaeoenvironment around lake loannina a type locality for the northern mediterranean region we show that both sets of evidence are compatible with a summer dry winter wet regime with seasonal temperature anomalies similar to those predicted by atmospheric model simulations of the last glacial maximum14 18 the drying effect of the cold north atlantic ocean may have been counteracted in winter by increased storm frequency under a southward shifted jet stream as shown by several atmospheric models16 18

relation of subtropical atlantic temperature high latitude ice rafting deep water formation and european climate 130 000 60 000 years ago abstract a new high resolution record of sea surface temperature from the subtropical western north atlantic documents a series of abrupt coolings within marine isotope stage 5 which can be objectively correlated with marine core evidence for increased ice sheet discharge at subpolar latitudes and reduced north atlantic deep water formation these results indicate that ice sheet forcing of deep ocean circulation influenced surface temperatures over much of the north atlantic a proposed correlation to the pollen record of grande pile france indicates that each cold event seen in the pollen sequence has a unique counterpart in the record of subtropical ocean temperature if this correlation is correct it suggests that the warmest part of the european eemian ended suddenly in response to oceanographic changes and that the subsequent post temperate phase of the eemian extended well into the interval of ice sheet growth corresponding to marine isotope substage 5d

variability of the western mediterranean sea surface temperature during the last 25 000 years and its connection with the northern hemisphere climatic changes sea surface temperature sst profiles over the last 25 kyr derived from alkenone measurements are studied in four cores from a w e latitudinal transect encompassing the gulf of cadiz atlantic ocean the alboran sea and the southern tyrrhenian sea western mediterranean the results document the sensitivity of the mediterranean region to the short climatic changes of the north atlantic ocean particularly those involving the latitudinal position of the polar front the amplitude of the sst oscillations increases toward the tyrrhenian sea indicating an amplification effect of the atlantic signal by the climatic regime of the mediterranean region all studied cores show a shorter cooling phase 700 years for the younger dryas yd than that observed in the north atlantic region 1200 years this time diachroneity is related to an intra yd climatic change documented in the european continent minor oscillations in the southward displacement of the north atlantic polar front may also have driven this early warming in the studied area during the holocene a regional diachroneity propagating west to east is observed for the sst maxima 11 5 10 2 kyr b p in the gulf of cadiz 10 9 kyr b p in the alboran sea and 8 9 8 4 kyr b p in the thyrrenian sea a general cooling trend from these sst maxima to present day is observed during this stage which is marked by short cooling oscillations with a periodicity of 730 40 years and its harmonics

on the timing and mechanism of millennial scale climate variability during the last glacial cycle the demonstration that natural climate variability during the last glacial cycle shifted rapidly between remarkable extremes has dramatically revised the understanding of climate change to further advance our understanding research continues into the timings geographic distribution and nature of the millennial scale climate extremes and into the mechanisms for intra and inter hemispheric transmission of variability through the climate ocean system complementing the traditional definition of the timings of millennial scale climate variability from ice core 18o records we here further narrow down the temporal constraints by determining statistically significant anomalies in the major ion series of the gisp2 ice core this exercise offers an objective definition of the timing of climatic anomalies in northern hemisphere palaeoclimate proxy records of the last 110 000 years that significantly improves the potential for inter calibration of ice core tuned chronostratigraphies we then present a process oriented synthesis of proxy records from the northern hemisphere this leads to a conclusion that the dansgaard oeschger d o style fluctuations in these records are virtually in phase since all fall within a clear atmospheric pattern of concerted relative dominance shifts between polar westerly dominated winter type conditions and tropical monsoon dominated summer type conditions finally we speculate on a monsoon related mechanism that could help explain the anomalously long duration of d o interstadials 12 8 and 1 which coincided with cooling trends in antarctic records

the role of atmospheric deposition in the biogeochemistry of the mediterranean sea abstract estimates of atmospheric inputs to the mediterranean and some coastal areas are reviewed and uncertainities in these estimates considered both the magnitude and the mineralogical composition of atmospheric dust inputs indicate that eolian deposition is an important 50 or even dominant 80 contribution to sediments in the offshore waters of the entire mediterranean basin model data for trace metals and nutrients indicate that the atmosphere delivers more than half the lead and nitrogen one third of total phosphorus and 10 of the zinc entering the entire basin measured data in sub basins such as the north western mediterranean and northern adriatic indicate an even greater proportions of atmospheric versus riverine inputs when dissolved fluxes are compared the form most likely to impinge on surface water biogeochemical cycles the atmosphere is found to be 5 to 50 times more important than rivers for dissolved zinc and 15 to 30 times more important for lead fluxes neglecting co limitation by other nutrients new production supported by atmospheric nitrogen deposition ranges from 2 4 g c m 2 yr 1 whereas atmospheric phosphorus deposition appears to support less than 1 g c m 2 yr 1 in spite of the apparently small contribution of atmospheric deposition to overall production in the basin it has been suggested that certain episodic phytoplankton blooms are triggered by atmospheric deposition of n p or fe future studies are needed to clarify the extent and causal links between these episodic blooms and atmospheric oceanographic forcing functions a scientific program aimed at elucidating the possible biogeochemical effects of saharan outbreaks in the mediterranean through direct sampling of the ocean and atmosphere before and after such events is therefore highly recommended

the general circulation of the mediterranean sea from a 100 year simulation results from a 120 year simulation of the mediterranean sea with a 1 4 19 level eddy permitting cox model with monthly varying wind and buoyancy forcing are presented mean and seasonal currents are examined along with water distributions on isopycnals detailed equilibrated thermohaline water pathways broadly consistent with observed hydrographic data are determined the most important factor permitting a long model run is low vertical mixing which maintains levantine intermediate water liw above the level of the sicily sill so that it can reach the western basin a new feature is tyrrhenian deep water which is formed after 40 years by deep water transfer from the balearic basin south of sardinia a water mass analysis reveals the modification of water properties in t s space through the mixing processes that take place at straits and through the action of mesoscale eddies the surface heat and freshwater fluxes derived a posteriori are in very good agreement with observations showing that basin average fluxes are closely tied to the generation of a realistic thermohaline circulation a complete analysis of surface and strait fluxes demonstrates that equilibrium conditions have been reached a study of the heat budget in the intermediate water layer at 280 m depth reveals that the dominant diabatic terms are at localized convection sites suggesting that at this depth the thermocline is under advective rather than diffusive control the eddy and mean flow heat transports balance to a large degree away from these sites with a negligible role for diffusion

enhanced aridity and atmospheric high pressure stability over the western mediterranean during the north atlantic cold events of the past 50 k y multiproxy paleoenvironmental records pollen and planktonic isotope from ocean drilling program site 976 alboran sea document rapid ocean and climate variations during the last glacial that follow the dansgaard oeschger climate oscillations seen in the greenland ice core records thus suggesting a close link of the mediterranean climate swings with north atlantic climates continental conditions rapidly oscillated through cold arid and warm wet conditions in the course of stadial interstadial climate jumps at the time of heinrich events i e maximum meltwater flux to the north atlantic western mediterranean marine microflora and microfauna show rapid cooling correlated with increasing continental dryness enhanced aridity conceivably points to prolonged wintertime stability of atmospheric high pressure systems over the southwestern mediterranean in conjunction with cooling of the north atlantic

palaeoclimate and palaeoenvironmental responses in the western mediterranean over the last 140 ka evidence from mallorca spain climatic change in the western mediterranean basin over the last 140 ka has been investigated from sediment and soil sequences along the coast of the northeastern part of mallorca spain palaeoclimate and palaeoenvironments are reconstructed from sediment and soil structures marine and terrestrial molluscan fauna grain size distributions mineral magnetics sediment and soil chemistry sem and oxygen isotope values dating is by osl and amino acid geochronometry along with marine molluscan faunal assemblages all oxygen isotope stages and substages from ois 6 to 1 are recorded mean annual temperatures m a t of c 19 2 c for the climatic optimum of the last interglacial compare with c 17 3 c for the present and are associated with high sea level extensive woodland and stable soils although wide temperature ranges are detected during this stage with values as low as c 10 3 c through ois 5d to 5a m a t fluctuated from 8 2 c to 17 9 c low sea level open vegetation effective river activity and aeolian sand and dust deposition characterize 5d and 5b while relatively high sea level and soil development on stable landscapes dominate ois 5c and 5a ois 4 is represented by m a t of c 4 9 c with aeolian sand and loess deposition limited river activity and weak soil development loess deposition persisted into ois 3 but at this time the m a t was c 13 c and with higher humidity and vegetation growth during the lgm ois 2 m a t was c 8 1 c and effective river slope and aeolian processes along with associated with limited vegetation cover were responsible for the most extensive changes in the landscape major rates of change occur during periods of climatic deterioration when the high levels of geomorphic energy were imposed on a landscape undergoing a breakdown of vegetation cover

textural and dispersal patterns of thick mud turbidites from the madeira abyssal plain abstract the madeira abyssal plain is the site of a thick sequence of thick pleistocene turbidites that are almost entirely of material less than 63 m in grain size the major turbidites are 1 to 5 m in maximum thickness concentrating on three turbidites cored at 24 locations detailed patterns of thickness and vertical and lateral grain size changes reveal flow paths on the plain in general the bases of the units are of graded silt showing thick and thin planar lamination and occasionally ripple cross lamination a new idealised sequence of changes in size and structures with distance along the flow path is developed closer to source the beds comprise a graded structured silty base overlain by structureless mud which may also be graded down current the silty base becomes thinner with less apparent structure and the upper homogeneous part becomes thicker and more uniform in an overall thickening trend at the distal end uniform beds up to 5 m in thickness are found in one turbidite the modal size structure shows some silt modes which are hydrodynamically sorted and change size vertically and spatially while one particular mode is constant in size due to a particular species of coccolith the turbidites originated from slumps on the northwest african continental margin and from the vicinity of madeira and the canaries some of which exceeded 100 km3 in volume

calculating erosion by deep sea turbidity currents during initiation and flow turbidity currents transport massive amounts of sediment from continental margins to the deep sea individual flows can catastrophically remove and redeposit as turbidites many hundreds of cubic kilometres of material1 2 with the larger events reaching the bottom of the continental slope to form the abyssal plains3 here we show that the age range of sediments in individual turbidites can be used directly to estimate both the thickness of failed sediment in the source region even when its exact location is unknown and the extent to which the turbidity current caused erosion of the sea bed our method involves the comparison of the abundance ratios of microfossil coccolith species in turbidites with those in the ocean margin sediments of the source region analysis of a recently emplaced turbidite on the madeira abyssal plain shows that it contains a mixture of sediments with an age range of about 200 000 years equivalent to the failure of a block of sediment about 15 m deep radiocarbon dating and coccolith ratios show that the turbidite contains only about 12 of recent near surface sediment indicating that this turbidity current caused surprisingly little erosion en route

low sea level emplacement of a very large late pleistocene megaturbidite in the western mediterranean sea large volume turbidites termed megaturbidites or megabeds result from catastrophic slope failures and the associated downslope transport of enormous quantities of sediment from continental margins to the deep sea such large sediment failures can generate tsunamis and in terrains underlain by gas hydrates clathrates may be associated with the release of substantial amounts of the greenhouse gas methane it has been proposed that the megaturbidite events may be triggered by seismic activity or may result from gas hydrate release itself caused by a lowering of hydrostatic pressure on clathrates as a result of low sea level previous conclusions on the significance of sea level change however have been conditional because of the lack of absolute times of turbidite emplacement here we use accelerator mass spectrometry radiocarbon dating in five widely spaced cores to constrain the date of emplacement of a large volume 500 km3 bed in the balearic basin of the western mediterranean this turbidite is exceptional in its magnitude and represents the main sedimentation event in the balearic basin over the past 100 kyr our data provide an estimate of 22 000 calendar years before present for emplacement of the megabed a time when sea level stood at its lowest level during the last glacial maximum the coincidence of these dates is consistent with emplacement due to clathrate destabilization caused by low sea level although other triggering mechanisms such as seismic shock cannot be ruled out

mineralogical composition of african dust delivered by red rains over northeastern spain the african dust deposition mineralogy source regions and influence on rain chemistry were analyzed for a site in the montseny mountains catalonia northeastern spain for the period august 1 1983 through august 1 1994 dust deposition was highly variable two events collected on november 9 11 1984 and march 22 25 1991 accounted for 62 of the total dust input in the 38 red rain events recorded in the period the average annual dust deposition was 5 3 g m 2 se 2 6 three source regions in the african continent were identified with back trajectory analysis 1 western sahara 2 moroccan atlas and 3 central algeria events from the moroccan atlas predominated in terms of number of events amount of rainfall and dust deposition the meteorological situations during red rains were identified western sahara events occurred principally with a depression at high latitudes 50 n forming a trough in the north atlantic moroccan atlas events occurred with a depression in front of portugal and events from central algeria were associated with a depression over spain or north africa by order of abundance median of n 13 the minerals identified in the dust by x ray diffraction were as follows illite quartz smectite palygorskite kaolinite calcite dolomite feldspars differences in mineralogy between source regions were significant for smectite kaolinite quartz and dolomite smectite and kaolinite content was highest in the algerian events while quartz and dolomite content was lowest events from the moroccan atlas had the lowest smectite and kaolinite the red rain soluble chemistry was clearly influenced by the dissolution of calcite high alkalinity calcium concentration and basic ph and by marine components high na cl arid mg 2 concentrations because of the very alkaline character of red rains they had a strong weight on the annual mean ph of rainwater this was reflected by the significant relationship r 0 71 p 0 01 between the percentage of annual precipitation as red rain and annual mean precipitation ph red rains provided 25 45 of the annual dissolved input of the major ions in precipitation and 34 of the calcium required for holm oak quercus ilex l forest growth at the study site