on the origin of the warm inflow to the nordic seas abstract warm and saline waters enter the nordic seas from the south as part of the warm to cold water transformation of the thermohaline circulation of the northern north atlantic one explanation for the origin of the nordic seas inflow is a shallow source hypothesis under which the inflow waters are a modification of upper ocean subtropical waters warm waters from the subtropical gyre are carried to the eastern north atlantic by the north atlantic current and branch northwards joined by poleward upper thermocline flow along the upper continental slope to provide the nordic seas inflow along this pathway the upper water column is progressively cooled and freshened by winter convection the subpolar mode water transformation process and this sets the inflow characteristics a deep source hypothesis provides an alternative explanation for the characteristics of the nordic seas inflow and the pathway delivering the waters to the inflow under this hypothesis inflow waters originate from the core of the mediterranean overflow waters in the gulf of cadiz carried northward at mid depth by the eastern boundary undercurrent in the subtropics continuing into the subpolar gyre along the eastern boundary and rising from depths near 1200m in the rockall trough to less than 600m to cross the wyville thomson ridge into the faroe shetland channel and thence to the nordic seas the deep source hypothesis focus is on lower thermocline source waters beneath the sill depth for the nordic seas inflow in contrast to the shallow source hypothesis focus of transformation of upper thermocline waters above the sill depth on the basis of regional water mass distributions geostrophic shear and direct current measurements we reject the deep source hypothesis in favor of the shallow source hypothesis rather than a flow of deep mediterranean overflow water along the eastern boundary rising from depth to feed the nordic seas the inflow is supplied directly by transformed north atlantic current waters from the same depth range as the inflow mediterranean overflow water is a constituent of the inflow but only through its contribution to defining the temperature salinity relationship of the interior of the subtropical gyre from which the north atlantic current draws its water rather than by direct northward advection of mediterranean outflow water via the eastern boundary undercurrent crossing from the subtropics into the subpolar domain instead the eastern boundary undercurrent wholly expels its transport of mediterranean overflow water into the eastern edge of the subtropical gyre creating the mid depth westward extending subtropical salinity plume for the lower thermocline isopycnal range of the core of the mediterranean overflow water measurements show that at the wyville thomson ridge the flow is southward and descending rather than northward and rising representing cold spillover from the faroese channels entraining warm upper ocean waters as the spillover plume descends and warms into the northern rockall trough no evidence is found in rockall trough northward of 54 n porcupine bank for direct advection of mediterranean overflow waters via an eastern boundary undercurrent extension and the very dilute mediterranean overflow waters in the trough reflect the interaction of the wyville thomson ridge plume descending into the trough from the north and lower thermocline waters delivered to the trough from the south

paleoceanographic and climatic implications of a new mediterranean outflow branch in the southern gulf of cadiz abstract the presence of contourite drifts in the southern gulf of cadiz goc along the moroccan margin raises questions about the re circulation of mediterranean outflow water mow in the goc and the origin of the currents depositing them here we compare two cores representative of iberian and moroccan contourite drifts covering the last 22 kyr although the whole sequence is contouritic in character it reflects the interaction of distinctive silty contourite facies high flow velocity periods imbedded in muddy contourite facies low flow velocity periods evidence from benthic foraminifera 13c sortable silt grain size oceanographic ctd profiles and numerical simulations indicate the mediterranean water mass as the source of the southern contourite deposits our data therefore suggests an additional branch of upper mow veering southwards off the straits of gibraltar along the moroccan margin during mis marine isotope stage 2 upper mow was a sluggish current while in the holocene upper mow dominated as a fast semi steady flow throughout the deglaciation silty contourites associated with higher flow speeds were deposited in the northern and southern goc during cold events such as heinrich stadial 1 hs1 and the younger dryas forced by global millennial scale climate variability millennial variability also appears to drive the deposition of silty contourites in the holocene we estimated an average duration of 1 ka for the process of depositing a fast contourite unit the case of silty contourite i6 within hs1 allows us to illustrate with extremely high resolution a rapid sequential change in circulation with gradual slow down of dense mediterranean water while surface was freshening hs1 provoking injection of high salinity intermediate waters via contour currents into the goc and hence the north atlantic the subsequent brief collapse of dense water formation in the mediterranean sea triggered a major increase in sea surface temperatures 10 c ka in the goc developing into the next interstadial bolling allerod the impact of mediterranean intermediate waters is manifested here by triggering a substantial rearrangement of intermediate and deep circulation in the north atlantic which would have further impacted the atlantic meridional overturning circulation amoc

environmental control on mediterranean salinity and δ18o a box model is presented to simulate changes in mediterranean long term average salinity and 18o over the past 20 000 years simulations are validated by comparison with observations sensitivity tests illustrate robustness with respect to the main assumptions and uncertainties the results show that relative humidity over the mediterranean remained relatively constant around 70 apparently narrowly constrained to the lower end of the range observed globally over sea surfaces by the basin s land locked character isotopic depletion in run off relative to the present is identified as the main potential cause of depletions in the mediterranean 18o record also slight increases in relative humidity of the order of 5 might have caused very pronounced isotopic depletions such as that in sapropel s5 of the penultimate interglacial maximum the model shows distinctly non proportional responses of 18o and salinity to environmental change which argues against the use of isotope residuals in mediterranean paleosalinity reconstructions

joint inversion of 2d resistivity and seismic travel time data to image saltwater intrusion over karstic areas the simultaneous inversion of multiple geophysical data types has been proven to be a powerful tool to both improve subsurface imaging and help in the interpretation process the main goal of this paper was to develop joint inversion strategies to provide improved resistivity and seismic velocity images for delineating saline water zones in karstic geological formations the cross gradient constraint approach was adopted to jointly invert resistivity and seismic first arrival data the basic idea of this approach is to quantitatively estimate the structural similarity between resistivity and seismic velocity models using the cross product of their gradients and to achieve a unified geological model which satisfies both data sets initially synthetic data were employed to help develop a joint inversion strategy to be used over such complex geological structures the proposed strategy uses a weighting factor for the cross gradient constraints and separate damping factors for the resistivity and seismic data this strategy was applied successfully on field data from the karstic region of stilos crete greece

facies distribution and textural variation in faro drift contourites velocity fluctuation and drift growth abstract detailed study of seismic profiles piston cores and bottom photographs from the faro drift on the southern margin of portugal has led to a better understanding of drift development and its relationship to bottom current circulation data on the contourite facies characteristics and the surface microphysiography have been published elsewhere here we concentrate on sediment distribution and geometry longitudinal trends in facies types mean grain size sedimentary structures and composition can be interpreted in terms of relative intensity of currents over different parts of the drift these are generally more intense in the marginal channels and at the upstream or eastern end of the drift three different scales of vertical variation of facies can be identified at the large scale 300 500 m of sediment has accumulated over 4 6 ma in a regular vertical succession due to the northward progradation of the drift at the medium scale the upper 20 30 m of sediment shows alternating phases of active lateral progradation and uniform vertical accumulation that may correlate with episodes of more and less current activity related to high and low sea level stands respectively over the past 0 3 ma at the small scale the topmost 2 3 m of sediment deposited in approximately 0 03 ma shows three zones of coarser grained sediments separated by finer grained contourites this sequence can also be interpreted in terms of long term fluctuation in bottom current activity although the signal is clearly complex this kind of analysis of sedimentary drifts can lead to more accurate reconstruction of paleocirculation patterns

high precision dating of the kalkarindji large igneous province australia and synchrony with the early middle cambrian stage 4 5 extinction the voluminous kalkarindji flood basalts erupted in australia during the cambrian and covered 2 x 10 6 km 2 new u pb and ar 40 ar 39 age data from intrusive rocks and lava flows yielded statistically indistinguishable ages at ca 511 ma suggesting a relatively brief emplacement for this province a zircon age of 510 7 0 6 ma shows that this province is temporally indistinguishable at the few hundred thousand year level from the early middle cambrian stage 4 5 boundary age of 510 1 ma which marks the first severe extinction of the phanerozoic and an extended marine anoxia period sulfur concentration measurements ranging from 50 to 1900 mu g g and fractal analysis of extensive explosive volcanic breccias suggest that blasts and phreatomagmatic explosions have contributed to injection of large amounts of sulfur into the stratosphere in addition magma intrusions in oil gas and sulfate deposits may have generated significant emission of ch4 and so2 which along with volcanic gases would have combined to cause an oscillation of the climate and led to the cambrian extinction less

cenomanian turonian carbon isotope events recorded in terrestrial organic matter from northern japan carbon isotopic fluctuations recorded in terrestrial organic matter from the upper cretaceous cenomanian turonian succession of hokkaido japan show a remarkably similar pattern to isotopic fluctuation in carbonate carbon reported from southern england and the italian apennines chronological correlation for the cenomanian turonian section of japan is based on planktonic foraminiferal biostratigraphy with some additional data from macrofossils allowing a detailed comparison of isotope stratigraphies for japan and europe three distinct features of the isotope profile namely a positive spike near the cenomanian turonian boundary a shoulder in the lower middle turonian and a level segment in the middle upper turonian are observed in japan these features are biostratigraphically comparable and correlative with isotope profiles reported from europe the single factor influencing isotopic composition of both terrestrial organic carbon and marine carbonate carbon is isotopic change in the global co2 reservoir of the ocean atmosphere system if these three carbon isotope features are synchronous they may be inferred as having been caused by global phenomena and as providing global high resolution chemo stratigraphic markers carbon isotope stratigraphy could be an important bridge between terrestrial inland sequences and marine sequences

mercury evidence from the sino korean block for emeishan volcanism during the capitanian mass extinction a prominent large negative 13 c org excursion and a coeval notable spike in mercury hg total organic carbon ratio are observed in the middle upper permian gohan formation in central korea located in the eastern sino korean block skb which may represent the capitanian mass extinction event the skb was separated from the south china block by the eastern palaeo tethys ocean this finding from the skb supports the widespread hg loading to the environment emitted from the emeishan volcanic eruptions in sw china this study demonstrates that the hg cycle was globally perturbed in association with global carbon cycle perturbation that occurred during the capitanian extinction

pliocene and quaternary depositional model of the algarve margin contourite drifts gulf of cadiz sw iberia seismic architecture tectonic control and paleoceanographic insights abstract the contourite drifts off southwest iberia that formed as a result of the interaction of the mediterranean outflow water mow with the continental middle slope were studied in the algarve margin using multichannel reflection seismic lines oil wells piston cores and a bathymetric compilation of four datasets the seismostratigraphic interpretation of a dense array of oil industry seismic and stratigraphic correlation allowed the identification of five seismic units of early pliocene through holocene in the faro and albufeira drifts and four correlative seismic units in the lagos and sagres drifts and three in the portimao drift a three phased evolutionary model for the contourite formation is proposed firstly a precursory phase of pliocene age made up of sheeted drifts represents an initial phase of deposition under bottom current activity that is correlated with the first stages of an enhanced mow at about 3 5 ma secondly the building up phase of early pleistocene age is related to a strengthening of the mow close to the onset of the northern hemisphere glaciations at about 2 6 ma during which were deposited low mounded drifts thirdly the growing phase from middle pleistocene through holocene suggests the presence of a stronger mow since the beginning of the middle pleistocene transition at about 1 3 1 0 ma accounting for the deposition of mounded drifts and formation of the alvares cabral moat seismostratigraphic interpretation and isochron maps allowed for the establishment of the main oceanographic climatic morphologic and tectonic factors that controlled the drifts deposition i the pliocene and quaternary mow circulation forced by climate changes ii the sea bottom topography inherited from the late miocene mainly shaped by the portimao lagos and bartolomeu dias canyons system iii the interaction between along slope and down slope processes since the pliocene and iv pliocene quaternary fault activity and diapirism

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

links between salinity variation in the caribbean and north atlantic thermohaline circulation variations in the strength of the north atlantic ocean thermohaline circulation have been linked to rapid climate changes1 during the last glacial cycle through oscillations in north atlantic deep water formation and northward oceanic heat flux2 3 4 the strength of the thermohaline circulation depends on the supply of warm salty water to the north atlantic which after losing heat to the atmosphere produces the dense water masses that sink to great depths and circulate back south2 here we analyse two caribbean sea sediment cores combining mg ca palaeothermometry with measurements of oxygen isotopes in foraminiferal calcite in order to reconstruct tropical atlantic surface salinity5 6 during the last glacial cycle we find that caribbean salinity oscillated between saltier conditions during the cold oxygen isotope stages 2 4 and 6 and lower salinities during the warm stages 3 and 5 covarying with the strength of north atlantic deep water formation7 at the initiation of the bolling allerod warm interval caribbean surface salinity decreased abruptly suggesting that the advection of salty tropical waters into the north atlantic amplified thermohaline circulation and contributed to high latitude warming

primary productivity variability on the atlantic iberian margin over the last 70 000 years evidence from coccolithophores and fossil organic compounds 1 this study analyzes coccolithophore abundance fluctuations e g emiliania huxleyi gephyrocapsa specimens and florisphaera profunda in core md01 2444 sediment strata retrieved at the iberian margin northeastern atlantic ocean coccolithophores are calcareous nannofossils a major component of the oceanic phytoplankton which provide information about past ecological and climatological variability results are supported by data on fossil organic compounds sea surface temperatures alkenones and n hexacosan 1 ol index and geochemical analyses benthic 13ccc and planktonic 18occ isotopes three scenarios are taken into account for this location at centennial scale resolution over the last 70 000 years the holocene and the stadial and interstadial modes the different alternatives are described by means of elements such as nutrients upwelling phenomena temperatures at surface and subsurface level or the arrival of surface turbid fresh and cold waters due to icebergs low sea level increased aridity and dust during the holocene moderate primary productivity was observed mainly concentrated in e huxleyi specimens surface temperatures were at maxima while the water column was highly ventilated by northern sourced polar deep waters and warmer subsurface nutrient poor subtropical waters over most of the last glacial stadials surface productivity weakened higher f profunda and reworked specimen percentages and lower diunsaturated and triunsaturated c37 alkenones the arrival of cold arctic surface waters traced by tetraunsaturated c37 peaks and large e huxleyi together with powerful ventilated southern sourced polar deep waters disturbed in all likelihood the delicate vertical equilibrium while preventing significant upwelling mixing finally during the last glacial interstadials lower f profunda percentages nonreworked material and higher diunsaturated and triunsaturated c37 alkenones a combined signal is observed warm surface temperatures were concurrent with generally low oxygenation of the deep sea floor moderate arrival of northern sourced deep waters and subsurface cold nutrient rich recently upwelled waters probably of polar origin these particular conditions may have promoted vertical mixing while enhancing surface primary productivity mainly of gephyrocapsa specimens

evidence from the northeastern atlantic basin for variability in the rate of the meridional overturning circulation through the last deglaciation a first study from the subtropical western atlantic using 231pa 230th ratios as a kinematic proxy for deep water circulation provided compelling evidence for a strong link between climate and the rate of meridional overturning circulation moc over the last deglaciation however these results warrant confirmation from additional locations and water depths because the interpretation of the sedimentary 231pa 230th ratio in terms of circulation vigor can be biased by variations in particle flux and composition we have measured 231pa 230th in a core from the iberian margin in the northeastern atlantic basin and have compared these new results to the data from the western atlantic basin we find that the reduction in the circulation during h1 and yd and the subsequent increases first recognized in the sediment deposited on bermuda rise are also evident in the eastern basin in a totally different sedimentary regime confirming that sedimentary 231pa 230th ratios record basin wide changes in deep water circulation however some differences between the eastern and western records are also recognized providing preliminary evidence to differentiate between renewal rates in the two north atlantic basins and between shallower and deeper overturning our results suggest the possible existence of two sources of glacial north atlantic intermediate deep water gnaiw one in the south labrador sea and another west of rockall plateau both sources contributed to the meridional overturning but the two had different sensitivity to meltwater from the laurentide and the fennoscandian ice sheets during the deglaciation these results indicate that additional information on the geometry and strength of the ventilation of the deep atlantic can be obtained by contrasting the evolution of sediment 231pa 230th in different sections of the atlantic ocean

late glacial to recent paleoenvironmental changes in the gulf of cadiz and formation of sandy contourite layers planktonic foraminifera and coccoliths were analyzed from six gravity cores obtained on a deep terrace located on the upper continental slope of the gulf of cadiz between 400 and 700 m water depth the lithology of these cores consists mainly of muds with some interbedded sandy or silty foraminifer rich layers that have been reported as contourites originated by the action of the mediterranean outflowing waters mow sweeping the sea bottom today after the last glacial characterized by muddy sedimentation sandy contourites start to deposit in the gulf of cadiz during the bolling allerod 14 11 14c kyr bp climatic optimum this trend was broken during the younger dryas 11 10 14c kyr bp and started again after the end of the younger dryas this pattern is recorded in most of the cores by a single sandy contourite layer formed during the first deglaciation stage bolling allerod time and a sandy contourite interval that initiates immediately after the end of the younger dryas during the second stage of the deglaciation and continues during the holocene the stratigraphy and climatic reconstruction was based on the evolution of the calcareous plankton assemblages during the last climatic transition from the last glacial to the recent holocene the sharp reduction of sinistral n pachyderma along with the reduction of g quinqueloba mark the base of bolling allerod time this is also related to a prominent peak of the subtropical species g sacculifer and g ruber the younger dryas is identified by a reduction in abundance of the subtropical species that again increase just after this period the second step of deglaciation is marked by a sharp decrease in the relative abundance of dextrally coiled n pachyderma in previous papers the sequence of sandy contourites has been related to sea level rise greater gibraltar sill depth and enhanced energy of the mow in this work we suggest that the individual sand layer episodes are condensed layers originating during times of rapid warming and relative sea level rise within the last deglaciation during these times the coastline migrated more rapidly landward and the terrigenous input decreased as it began to be trapped on land and on the shelf resulting in a major drop in sedimentation rate on the upper continental slope in times of low sedimentation rate the particles would have a longer residence time within the upper mixed layer of the near surface sediment and therefore the energy of currents would act longer producing a more efficient winnowing of the sediment at the same time more generations of benthic organisms would rework the mixed layer favoring this winnowing

deglacial sea level record from tahiti corals and the timing of global meltwater discharge the timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets1 and their effects on the earth s surface2 3 moreover the disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans which probably disturbed the ocean s thermohaline circulation and hence global climate4 7 sea level increases bear witness to the melting of continental ice sheets but only two such records from barbados8 9 and new guinea10 11 corals have been accurately dated but these corals overlie active subduction zones where tectonic movements are large and often discontinuous especially in new guinea so the apparent sea level records may be contaminated by a complex tectonic component here we date fossil corals from tahiti which is far from plate boundaries and thus is likely to be tectonically relatively stable and remote from the locations of large former ice sheets the resulting record indicates a large sea level jump shortly before 13 800 calendar years bp which corresponds to meltwater pulse 1a in the barbados coral records8 9 the timing of this event is more accurately constrained in the tahiti record revealing that the meltwater pulse coincides with a short and intense climate cooling event12 15 that followed the initiation of the bolling allerod warm period12 16 but preceded the younger dryas cold event by about 1 000 years

position of the polar front along the western iberian margin during key cold episodes of the last 45 ka 1 this paper documents the migration of the polar front pf over the iberian margin during some of the cold climatic extremes of the last 45 ka it is based on a compilation of robust and coherent paleohydrological proxies obtained from eleven cores distributed between 36 and 42 n planktonic 18o globigerina bulloides ice rafted detritus concentrations and the relative abundance of the polar foraminifera neogloboquadrina pachyderma sinistral were used to track the pf position these three data sets compared from core to core show a consistent evolution of the sea surface paleohydrology along the iberian margin over the last 45 ka we focused on five time slices representative of cold periods under distinct paleoenvironmental forcings the 8 2 ka event and the younger dryas two recent cold events occurring within high values of summer insolation heinrich events 1 and 4 reflecting major episodes of massive iceberg discharges into the north atlantic and the last glacial maximum typifying the highest ice volume accumulated in the northern hemisphere for each event we generated schematic maps mirroring past sea surface hydrological conditions the maps revealed that the polar front presence along the iberian margin was restricted to heinrich events the sea surface conditions during the last glacial maximum were close to those at present day except for the northern sites which briefly experienced subarctic conditions

radiation and extinction patterns in permian floras from north china as indicators for environmental and climate change abstract permian continental sequences from north china contain previously unrecognized episodes of plant radiation and elevated extinction the earliest extinction in the lower shihhotse formation roadian guadalupian records a 45 floral species loss and is tentatively correlated with global extinctions amongst dinocephalian reptiles two younger extinctions are dated by correlating the illawara reversal and palaeomagnetic polarity sequences from shanxi province against global palaeomagnetic history missing data from the shanxi sequence are evaluated using a novel approach estimating likely maximum and minimum sequence changes that provide age estimates for post illawara events in north china the second extinction in the middle upper shihhotse formation is more significant and is dated to the mid capitanian with a loss of 56 of plant species coinciding with two phases of volcanism of the emeishan large igneous province in south china previously linked to the mid capitanian marine mass extinction the youngest extinction in the upper upper shihhotse formation late capitanian to mid wuchapingian is catastrophic and represents the end of range in the sequence changes in sedimentary facies suggest it to be related to global climatic warming and drying other viable causal mechanisms for the extinction episodes include plate motion and collision global climate change volcanism and biological competition

qualitative and quantitative approaches in palaeohydrography a case study from core top parameters in the gulf of cadiz palaeoceanography relies on the assumption that parameters measureable in sediment cores correlate reliably to hydrographic parameters areas of dynamic watermass mixing which generally have steep hydrographic gradients therefore provide both a tempting target large spatial and temporal differences in temperature and salinity and a significant challenge high flow velocities and high noise for palaeoceanographers here we investigate the ability of parameters measured on core tops to be used as the basis for simulating regional hydrography within one globally important area of watermass mixing the gulf of cadiz using grainsize sediment composition benthic foraminiferal assemblage and benthic foraminiferal stable isotope analysis it is possible to build an effective framework for qualitative constraint of the position of the modern mediterranean outflow water mw plume we propose that the gulf of cadiz slope can be sub divided into 8 hydrographic zones reflecting these parameters proximal mw core mw1 steep slopes core mw1 gentle slopes distal mw1 distal mw2 lower limit of mw plume north atlantic deep water and ambient atlantic water we anticipate that compilation of time slice data will reveal hydrographic sub divisions of the slope for the past in a similar manner improving our understanding of past changes in the size and position of the mw plume but more work needs to be done before a secure protocol for quantitative reconstruction can be created stable isotope analysis alone is insufficient for the task with 13c behaving in a non conservative manner and 18ocalcite acting in an ambiguous way due to the competing influences of 18owater and temperature it is likely that if a single parameter that unambiguously determines the difference between mediterranean water and atlantic water can be identified combination with 18ocalcite will allow extension of our qualitative analysis into a quantitative means of palaeohydrographic reconstruction for this region similar complexity to that found in this study would be expected in any mixing region and in particular on the majority of sediment drifts we recommend that core top surveys similar to this study are performed on these sediment drift systems before any form of quantitative palaeohydrology is attempted

directly measured mid depth circulation in the northeastern north atlantic ocean the circulation of water masses in the northeastern north atlantic ocean has a strong influence on global climate owing to the northward transport of warm subtropical water to high latitudes but the ocean circulation at depths below the reach of satellite observations is difficult to measure and only recently have comprehensive direct observations of whole ocean basins been possible here we present quantitative maps of the absolute velocities at two levels in the northeastern north atlantic as obtained from acoustically tracked floats we find that most of the mean flow transported northward by the gulf stream system at the thermocline level about 600 m depth remains within the subpolar region and only relatively little enters the rockall trough or the nordic seas contrary to previous work our data indicate that warm saline water from the mediterranean sea reaches the high latitudes through a combination of narrow slope currents and mixing processes at both depths under investigation currents cross the mid atlantic ridge preferentially over deep gaps in the ridge demonstrating that sea floor topography can constrain even upper ocean circulation patterns

new insights into upper mow variability over the last 150kyr from iodp 339 site u1386 in the gulf of cadiz the upper mediterranean outflow water mow paleo oceanographic history in the gulf of cadiz is poorly constrained due to the lack of high resolution records that pre date the last glaciation existing proxy records concentrate on mow variability along the middle slope of the gulf of cadiz here we present a continuous high resolution benthic foraminifera 18o record from the upper mow core at iodp expedition 339 site u1386 in the gulf of cadiz of the past 150 000 years based on 18o grain size and zr al variability comparison of our results with existing mediterranean sea md01 2472 md95 2043 open ocean lr04 and gulf of cadiz md99 2339 records we have gathered new insights into the evolution of the upper mow core on glacial interglacial timescales the influence of the upper mow at site u1386 was strongest during mis 5 and mis 1 similar 18o variability can be seen in the levantine intermediate water liw originating from the levantine basin of the eastern mediterranean sea we found clear indication for a vertical shift of the mow from the upper to the middle slope of the gulf of cadiz during sea level lowstands coinciding with mis 4 and mis 2 but also during mis 3 additionally our results indicate an increased upper mow flow correlated with heinrich events 7 to 10 and the younger dryas and also inversely relate to precession forced monsoonal freshwater inputs into the eastern mediterranean in the context of sapropel formation we could not find conclusive evidence of the proposed mow shutdown in our data

sensitivity of mediterranean thermohaline circulation to gateway depth a model investigation 1 the neogene sedimentary record of the mediterranean sea holds evidence for changes in water properties and circulation these paleoceanographic changes have been attributed to changes in the flow through the ocean gateway between the mediterranean sea and the atlantic ocean we use an oceanic general circulation model to achieve quantitative physics based understanding of the effect of changes in the depth of the gateway such as may result from tectonic activity or variation in sea level to isolate these effects we use idealized basin geometry and impose simplified atmospheric forcing a reference experiment with present day sill depth demonstrates that the model simulates reasonably well the main features of the present day mediterranean thermohaline circulation as inferred from observations and previous numerical studies subsequently a series of sensitivity simulations is performed with different sill depths the model results show that mediterranean temperature salinity and thermohaline circulation depend strongly on sill depth as the sill depth decreases the upper overturning cell is quasi linearly reduced in strength while contrary to what one would expect the deep cell intensifies and does so in a nonlinear way we find that a shoaling of the sill depth induces a blocking effect on the outflow waters which creates a strong recirculation in the deep layers strengthening the deep cell nevertheless deep water formation is reduced and as a consequence the ventilation of the deep layers diminishes we identify three different circulation modes of the mediterranean thermohaline circulation depending on the sill depth shallow sill moderate sill and deep sill modes coupled with strong weak and negligible blocking effects respectively our results are consistent with the pre messinian paleoceanographic record of the mediterranean sea and may be useful to understanding the behavior of other land locked basins both extant and from the geological past

messinian productivity changes in the northeastern atlantic and their relationship to the closure of the atlantic mediterranean gateway implications for neogene palaeoclimate and palaeoceanography the stable isotope composition of planktic and benthic foraminifera and the distribution of selected benthic foraminiferal species from a messinian record of the lower guadalquivir basin northeastern atlantic ocean show that regional productivity changes were linked to glacioeustatic fluctuations glacial periods were characterized by poorly ventilated bottom waters as a result of weak atlantic meridional overturning circulation amoc and by phases of high productivity related to intensified upwelling in contrast well ventilated bottom waters owing to strong amoc the presence of degraded organic matter in the upper slope and high input of degraded terrestrial organic matter derived from fluvial discharge to the outer shelf were recorded during interglacial periods before closure of the adjacent guadalhorce corridor at 6 18 ma which was the final active betic atlantic mediterranean gateway the study area was alternately influenced by well ventilated mediterranean outflow water mow and poorly ventilated atlantic upwelled water auw following closure of the corridor cessation of the mow reduced the amoc and promoted glacial conditions in the northern hemisphere resulting in the establishment of local upwelling cells

contourite characterization and its discrimination from other deep water deposits in the gulf of cadiz contourite depositional system this project was funded through the joint industry project supported by bp eni exxonmobil total wintershall dea and tgs within the framework of the drifters research group at royal holloway university of london rhul in conjunction with the projects ctm 2012 39599 c03 cgl2015 66835 p ctm2016 75129c3 1 r cgl2016 80445 r aei feder ue and b rnm 072 ugr18 this research used data and samples collected by iodp expedition 339 aboard the joides resolution data was acquired at the xrf core scanner lab at marum center for marine environmental sciences university of bremen germany our thanks to dr javier dorador rhul uk for the high resolution core imaging treatment to dr david roque icman csic spain for his help in the hydrographic panels from fig 2 and to dr angel puga bernabeu university of granada spain for revision that helped to improve the original version of the manuscript before submission this study significantly benefited from discussions with all who attended the iodp exp 339 mow meeting in heidelberg germany in january 2019 we would like to thank associate editor dr adam mcarthur and the three reviewers dr rachel brackenridge dr giancarlo davoli and dr adriano viana for their positive and constructive comments that helped us improve the manuscript

late paleozoic macrofloral assemblages from weibei coalfield with reference to vegetational change through the late paleozoic ice age in the north china block abstract based on investigations of seven stratigraphic sections in the weibei coalfield a typical coal basin in the north china block the succession of late paleozoic plant macrofossil assemblages from the benxi or penchi in old spelling taiyuan shanxi lower shihhotse and upper shihhotse formations were redefined these zones are the paripteris spp linopteris spp conchophyllum richthofenii assemblage benxi fm neuropteris pseudovata lepidodendron posthumii assemblage taiyuan and lower shanxi fms emplectopteridium alatum emplectopteris triangularis cathaysiopteris whitei assemblage upper shanxi and lower shihhotse fms gigantonoclea lagrelii fascipteris hallei lobatannularia heianensis assemblage upper shihhotse fm as a result of this biostratigraphic reanalysis it has become clear that biostratigraphic boundaries do not exactly correlate to lithostratigraphic boundaries as has been thought the biostratigraphy of the terrestrial deposits in the north china block were correlated to the iugs global chronostratigraphy the more precise chronostratigraphic constraints that were obtained as a result of this study make it possible to more precisely correlate the vegetational successions to the concurrent waxing and waning of the late paleozoic ice sheets

is ocean thermohaline circulation linked to abrupt stadial interstadial transitions abstract are the abrupt stadial interstadial s is climate transitions observed in the greenland ice cores also seen in marine climate records literature which shows that the s is events have a large footprint in ocean surface marine properties encompassing the entire northern hemisphere has been reviewed whether this influence extends to the deep circulation is more equivocal on most recent evidence several of the heinrich ice rafting debris events are clearly associated with elimination of north atlantic source waters from the deep atlantic but most cores studied do not resolve the other s is events except for one new record from the bermuda rise which shows all of the major s is cycles in benthic foraminiferal deep sea corals can tell us how rapid these events are in the deep sea

persistent monsoonal forcing of mediterranean outflow water dynamics during the late pleistocene the mode and vigor of the global oceanic circulation critically depend on the salinity of sub surface water masses advected to the loci of deep water formation within the atlantic meridional overturning circulation amoc an important supplier of high salinity waters is the mediterranean outflow water mow discharging into the north atlantic via the strait of gibraltar despite its importance for the north atlantic salinity budget the long term dynamics of mow production have remained poorly understood here we present high resolution records of bottom current velocity from three drill sites within the gulf of cadiz that document a persistent low latitude forcing of mow flow speed over the past 150 k y we demonstrate that the african monsoon is the predominant driver of orbital scale mow variability via its influence on the freshwater budget of the eastern mediterranean sea consequently mow formation fluctuates in concert with orbital precession overprinted by centennial scale oscillations of high latitude origin we further document that northern hemisphere summer insolation minima stimulate maximal injection of mow derived salt into the north atlantic likely strengthening the intermediate amoc branch the direct coupling of mow dynamics to low latitude climate forcing represents a hitherto neglected process for propagating sub tropical climate signals into the high northern latitudes

analysis of salinization processes in the coastal carbonate aquifer of porto torres nw sardinia italy the porto torres nw sardinia coastal aquifer is hosted in the carbonate rocks of the miocene succession which fills a nnw oriented half graben this aquifer is an important contributor to the fresh water supply of the local area it is increasingly being degraded by salinization processes mainly associated with intense groundwater over exploitation a combined hydrochemical and hydrogeological study has been carried out to identify the origin of the salinity in the groundwater the behavior of the major ions showed that the changes in the chemical composition of the groundwater have been mainly controlled by the encroachment of seawater accompanied by cation exchange reactions since seawater intrusion is a dynamic process an hydrochemical facies evolution diagram hfe d gimenez forcada 2010 approach was taken to establish whether the aquifer was in the seawater intrusion or in the freshening phase the assessment model developed provides regional authorities with a basic tools for sustainable water management in the framework of multi disciplinary research activities aiming to combat and or mitigate desertification and land degradation processes

millennial to centennial scale climate periodicities and forcing mechanisms in the westernmost mediterranean for the past 20 000 yr abstract cyclostratigraphic analysis conducted on a continuous high resolution marine record from the western most mediterranean reveals well identified paleoclimate cycles for the last 20 000 yr the detrital proxies used si al ti al zr al mg al k al rb al are related to different sediment transport mechanisms including eolian dust and fluvial runoff which involve fluctuations in the atmosphere hydrosphere systems these fluctuations are accompanied by changes in marine productivity supported by ba al and bottom water redox conditions cu al v al zn al fe al mn al u th spectral analysis conducted using the lomb scargle periodogram and the achieved significance level implemented with the permutation test allowed us to establish major periodicities at 1300 1515 2000 and 5000 yr and secondary peaks at 650 1087 and 3000 yr some of these cycles also agree with those previously described in the north atlantic ocean and circum mediterranean records the periodicities obtained at 2000 and 5000 yr support a global connection with records distributed at high mid and low latitudes associated with solar activity monsoonal regime and orbital forcing the 1300 and 1515 yr cycles appear to be linked with north atlantic climate variability and the african monsoon system thus the analyzed record provides evidence of climate cycles and plausible forcing mechanisms coupled with ocean atmosphere fluctuations

timing of collision of the north and south china blocks controversy and reconciliation the qinling orogen was formed by the joining of the north and south china blocks but the timing of their integration has been debated for more than a decade the controversies obviously stem from different approaches to reconstruction of the integration history two contrasting lines of evidence yield two different ages for collision of the north and south china blocks middle paleozoic and late triassic the shangdan suture within the qinling was regarded in previous studies as the trace along which the north and south china blocks collided our studies however demonstrate that there are two sutures within the qinling the well documented shangdan suture and the newly discovered mianlue suture we show in this paper that the late proterozoic to early mesozoic evolution of the qinling involved interactions between the north china block the north and south qinling orogens and the south china block the middle paleozoic collision along the shangdan suture as constrained by some evidence accreted only the south qinling orogen to the southern part i e the north qinling of the north china block contemporaneous rifting of the south china block and subsequent drifting separated the south qinling from the south china block during the middle to late paleozoic the separation of the south from the north china blocks is supported by other evidence in particular geomagnetic data evidently it was the late triassic collision of the south china block with the south qinling orogen along the mianlue suture that led to final integration of the north and south china blocks

mapping a bedrock surface under dry alluvium with shallow seismic reflections shallow seismic reflection techniques were used to image the bedrock alluvial interface near a chemical evaporation pond in the texas panhandle allowing optimum placement of water quality monitor wells the seismic data showed bedrock valleys as shallow as 4 m and accurate to within 1 m horizontally and vertically the normal moveout velocity within the near surface alluvium varies from 225 m s to 400 m s all monitor well borings near the evaporation pond penetrated unsaturated alluvial material on most of the data the wavelet reflected from the bedrock alluvium interface has a dominant frequency of around 170 hz low cut filtering at 24 db octave below 220 hz prior to analog to digital conversion enhanced the amplitude of the desired bedrock reflection relative to the amplitude of the unwanted ground roll the final bedrock contour map derived from drilling and seismic reflection data possesses improved resolution and shows a bedrock valley not interpretable from drill data alone

a hydraulic box model study of the mediterranean response to postglacial sea level rise 1 this paper quantifies the role of changing sea level in affecting mediterranean stratification using a new model of the strait basin system which allows for explicit time dependence during the last deglaciation fairbank s meltwater peak 1b leads to rapidly rising global sea levels and a freshening of the oceans and hence increasing influx of ever freshening atlantic water into the mediterranean basin owing to long residence times the salinity of the deep and intermediate water reservoirs would have decreased more slowly so that the basin was more stably stratified for a period with possible implications for sapropel formation our model is used to estimate the size of this reservoir effect in comparison to the freshwater influx from the opening of the black sea at the bosphorus it is found that this mechanism affects the stratification to a similar degree as the black sea opening other climatic mechanisms have also affected the freshwater budget of the mediterranean at this time but their sizes are more difficult to quantify

mercury as a proxy for volcanic activity during extreme environmental turnover the cretaceous paleogene transition abstract the usually low geological background concentrations of hg makes this trace element suitable for identifying accumulation pulses in sediments that can be tentatively related to weathering processes and thus to climatic changes intense volcanism has witnessed the cretaceous paleogene transition ktb and was perhaps responsible for dramatic climatic changes and decrease in biodiversity and mass extinction we have used hg concentrations as a proxy for volcanic activity and atmospheric hg and co2 buildup across the ktb at three localities in the salta basin argentina hg contents display several spikes across the ktb with a maximum value of 250 ng g 1 in three drill cores across the ktb in the paraiba basin northeastern brazil hg contents increase from the late maastrichtian to early danian and hg spikes predate the ktb perhaps as a record of volcanic activity before but very close to this transition at stevns klint denmark hg contents reached almost 250 ng g 1 within a 5 cm thick clay layer the fiskeler member fish clay that comprises the ktb some co variation between hg and al2o3 contents has been observed in all of the studied sections across the ktb suggesting that hg is probably adsorbed onto clays thermo desorption experiments in selected samples from the yacoraite formation showed hg 2 as the major species present which is in agreement with a volcanic origin combined hg and c isotope chemostratigraphy may become a powerful tool for the eventual assessment of the role of volcanic activity during extreme climatic and biotic events such as those during the ktb

aridity of the mediterranean sea at the last glacial maximum a reinterpretation of the δ18o record paleoclimate data show conflicting evidence for aridity in the mediterranean basin at the last glacial maximum lgm two recent modeling studies of the lgm mediterranean using water balance biome and ocean general circulation models respectively suggest that evaporation over the basin was reduced at the lgm compared with today in apparent conflict with these results is the strongly enhanced 18o signature of the lgm mediterranean surface waters particularly in the eastern basin which has been ascribed to a much higher salinity in an alternative interpretation presented here a box model of the balance between paleoclimate model evaporation and rainfall and paleoceanographic model advective terms shows that the observed lgm 18o signature can be reproduced without the need for an enhanced salinity with advection playing the dominant role in the 18o budget the box model also shows that the 18o data alone are insufficient to determine the type of exchange between the eastern and western basins the results emphasize that regional paleoceanographic water balances should consider all relevant processes and not just the evaporative flux

geophysical approach to the environmental study of a coastal plain in the study of coastal plains affected by soil and water salination a knowledge of several geological aspects such as structural features depth to basement stratigraphy of sedimentary cover relationships between the phreatic aquifer and underlying aquifers and the latter s structure is basic to gaining an adequate understanding of both the causes and possible evolution of salination in this framework geophysical techniques can play a very important role to improve the available geophysical information about the muravera coastal plain sardinia italy which is affected by severe soil and water salination previously acquired electrical resistivity reflection seismic and gravity data have been reprocessed and a new seismic reflection survey has been conducted moreover in order to give better support to the geological and hydrogeological interpretation of geophysical data three boreholes were drilled reprocessed electrical data indicate the presence of a wide electrically homogeneous low re

contrasting sea surface responses between the western mediterranean sea and eastern subtropical latitudes of the north atlantic during abrupt climatic events of mis 3 abstract dinoflagellate cyst dinocyst analysis was conducted on two cores from the sw iberian margin and central alboran sea from which high quality records of marine isotope stage 3 have been previously derived our aim in this study is to compare the dinocyst signature between 50 and 25 ka bp with existing datasets of foraminiferal and geochemical proxies related to hydrological parameters quantitative reconstructions of sea surface temperatures ssts and salinities sss based on dinocysts are performed for the first time in this area the results are compared to ssts derived from planktonic foraminifera and alkenone measurements and to sss calculated from planktonic 18 o and foraminiferal sst significant oscillations related to dansgaard oeschger cycles are recorded in both cores dinocyst derived hydrological parameters exhibit synchronous fluctuations and similar values to those derived from the other methods in particular when considering quantitative reconstructions for february based on foraminifera and dinocysts our study shows that the influence of subpolar waters was felt during each greenland stadial gs off portugal and that the amplification of the heinrich stadial cooling in the alboran sea was related to the penetration of subpolar waters through the strait of gibraltar during greenland interstadials gi we provide evidence for the occurrence of warm and nutrient rich sea surface waters in the alboran sea probably due to gyre induced upwelling finally the difference between august and february dinocyst sst estimates suggests higher seasonal contrasts during gs compared to gi at the two core sites additionally precession appears to have an imprint on dinocyst derived long term seasonality record however this observation needs to be confirmed by longer records

ten years of marine current measurements in espartel sill strait of gibraltar more than 10 year of acoustic doppler current profiler observations collected at the westernmost sill espartel sill of the strait of gibraltar by a monitoring station have been carefully processed to provide the most updated estimation of the mediterranean outflow a comprehensive quality control of the factors affecting the uncertainty of the measurements has been carried out and great care has been paid to infer the current at the bottom layer where direct observations are lacking the mean outflow in the southern channel of the sill section has been estimated as 0 82 sv 1 sv 1 106 m3 s 1 with an average contribution of the eddy fluxes of 0 04 sv this figure is an overestimation as the mooring measurements assumed valid for the whole section ignore the lateral friction on the other hand it only gives the flow through the southern channel and disregards the fraction flowing through shallower northern part both drawbacks have been addressed by investigating the cross strait structure of the outflow from hindcasts produced by the mitgcm numerical model run in a high resolution domain covering the gulf of cadiz and alboran sea basins an overall rectifying factor of 1 039 was found satisfactory to correct the first estimate so that the final mean outflow computed from this data set is 0 85 sv complemented with an uncertainty of 0 03 sv based on the interannual variability of the series the temporal analysis of the series shows an outflow seasonality of around the 8 of the mean value with maximum outflow in early spring

glacial mediterranean sea surface temperatures based on planktonic foraminiferal assemblages we present a new reconstruction of mediterranean sea surface temperatures sst during the last glacial maximum lgm a calibration data set based on census counts of 23 species of planktonic foraminifera in 129 north atlantic and 145 mediterranean core top samples was used to develop summer winter and annual average sst reconstructions using artificial neural networks anns and the revised analogue method ram prediction errors determined by cross validation of the calibration data set ranged between 0 5 and 1 1 c with both techniques being most successful in predicting winter ssts glacial reconstructions are based on a new expanded data set of 273 samples in 37 cores with consistent minimum level of age control the new lgm reconstructions suggest that the east west temperature gradient during the glacial summer was 9 c whereas during the glacial winter the gradient was 6 c both some 4 c higher than that existing today in contrast to earlier studies our results tend to suggest much cooler sst estimates throughout the glacial mediterranean particularly in the eastern basin where previous sst reconstructions indicated a decrease of only 1 c our new sst reconstructions will provide the modelling community with a detailed and updated portrayal of the mediterranean sea during the lgm setting new targets on which glacial simulations can be tested

mediterranean undercurrent sandy contourites gulf of cadiz spain abstract the pliocene quaternary pattern of contourite deposits on the eastern gulf of cadiz continental slope results from an interaction between linear diapiric ridges that are perpendicular to slope contours and the mediterranean undercurrent that has flowed northwestward parallel to the slope contours and down valleys between the ridges since the late miocene opening of the strait of gibraltar coincident with the northwestward decrease in undercurrent speeds from the strait there is the following northwestward gradation of sediment facies associations 1 upper slope facies 2 sand dune facies on the upstream mid slope terrace 3 large mud wave facies on the lower slope 4 sediment drift facies banked against the diapiric ridges and 5 valley facies between the ridges the southeastern sediment drift facies closest to gibraltar contains medium fine sand beds interbedded with mud the adjacent valley floor facies is composed of gravelly shelly coarse to medium sand lags and large sand dunes on the valley margins compared to this the northwestern drift contains coarse silt interbeds and the adjacent valley floors exhibit small to medium sand dunes of fine sand further northwestward sediment drift grades to biogenous silt near the faro drift at the portuguese border because of the complex pattern of contour parallel and valley perpendicular flow paths of the mediterranean undercurrent the larger scale bedforms and coarser grained sediment of valley facies trend perpendicular to the smaller scale bedforms and finer grained contourite deposits of adjacent sediment drift facies the bottom current deposits of valleys and the contourites of the cadiz slope intervalley areas are distinct from turbidite systems the valley sequences are not aggradational like turbidite channel levee complexes but typically exhibit bedrock walls against ridges extensive scour and fill into adjacent contourites transverse bedform fields and bioclastic lag deposits both valley and contourite deposits exhibit reverse graded bedding and sharp upper bed contacts in coarse grained layers low deposition rates and a regional pattern of bedform zones textural variation and compositional gradation the surface sandy contourite layer of 0 2 1 2 m thickness that covers the gulf of cadiz slope has formed during the present holocene high sea level because high sea level results in maximum water depth over the gibraltar sill and full development of the mediterranean undercurrent the late pleistocene age of the mud underlying the surface sand sheet correlates with the age of the last sea level lowstand and apparent weak mediterranean undercurrent development thus the cyclic deposition of sand or mud layers and contourite or drape sequences appear to be related to late pliocene and quaternary sea level changes and mediterranean water circulation patterns since its pliocene origin the contourite sequence has had low deposition rates of

carbon isotope record of the early jurassic toarcian oceanic anoxic event from fossil wood and marine carbonate lusitanian basin portugal thetoarcianoceanicanoxicevent oae intheearlyjurassic 183maago wascharacterizedbywidespreadnear synchronous deposition of organic rich shales in marine settings as well as perturbations to several isotopic systems characteristically two positive carbon isotope excursions in a range of materials are separated by an abrupt negative shift carbon isotope profiles from toarcian fossil wood collected in england and denmark have previously been shown to exhibit this large drop 7 i n 13 c values interpreted as due to an injection of isotopically light co2 into the ocean atmosphere system however the global nature of this excursion has been challengedonthebasisofcarbon isotopedatafromnektonicmarinemolluscs belemnites whichexhibitheavierthanexpectedcarbonisotope values here we present new data principally from fossil wood and bulk carbonate collected at centimetre scale from a hemipelagic section at peniche coastal portugal this section is low in organic carbon average toc 0 5 and the samples should not have suffered significant diagenetic contamination by organic carbon of marine origin the carbon isotope profile based on wood shows two positive excursions separated by a large and abrupt negative excursion which parallels exactly the profile based on bulk carbonate samples from the same section albeit with approximately twice the amplitude 8 in wood versus 3 5 in carbonate these data indicate thatthe negative carbon isotope excursion affected the atmosphereand by implication the global ocean as well the difference in amplitude between terrestrial organic and marine carbonate curves can be explained by greater water availability in the terrestrial environment during the negative excursion for which there is independent evidence from marine osmiumisotope records and plausibly changes in atmospheric co2 content for which independent evidence is also available the peniche succession is also notable for the occurrence of re deposited sediments their lowest occurrence coincides with the base of the negative excursionandtheirhighestoccurrencecoincideswithitstop thus slopeinstabilityandsedimentsupplycouldhavebeenstronglylinked to the global environmental perturbation an association that may misleadingly simulate the effects of sea level fall

southern ocean origin for the resumption of atlantic thermohaline circulation during deglaciation during the two most recent deglaciations the southern hemisphere warmed before greenland at the same time the northern atlantic ocean was exposed to meltwater discharge which is generally assumed to reduce the formation of north atlantic deep water yet during deglaciation the atlantic thermohaline circulation became more vigorous in the transition from a weak glacial to a strong interglacial mode here we use a three dimensional ocean circulation model to investigate the impact of southern ocean warming and the associated sea ice retreat on the atlantic thermohaline circulation we find that a gradual warming in the southern ocean during deglaciation induces an abrupt resumption of the interglacial mode of the thermohaline circulation triggered by increased mass transport into the atlantic ocean via the warm indian ocean and cold pacific ocean water route this effect prevails over the influence of meltwater discharge which would oppose a strengthening of the thermohaline circulation a southern ocean trigger for the transition into an interglacial mode of circulation provides a consistent picture of southern and northern hemispheric climate change at times of deglaciation in agreement with the available proxy records

combined time domain electromagnetic soundings and gravimetry to determine marine intrusion in a detrital coastal aquifer southern spain summary marine intrusion is undoubtedly the most serious problem facing coastal aquifers that are exploited for use it is also an excellent indicator of the state of the aquifers resources this work proposes the combined application of two complementary geophysical techniques as an effective method for locating the saline wedge on one hand time domain electromagnetic soundings are the most reliable geophysical method for determining low resistivity zones that usually correspond to the presence of seawater although in some cases low resistivities may be due to the properties of the substrate on the other hand gravimetry allows a precise determination of the depth of the aquifer basement thus resolving the above uncertainty information provided by the lithological columns from boreholes has also allowed great precision in the calibration of the results from both techniques this methodology has been applied to the motril salobrena detrital coastal aquifer which has had no problems of marine intrusion to date nonetheless changes in soil use brought about by housing developments golf courses and a proliferation of hothouse agriculture comprise significant shifts in aquifer use in addition the construction of a dam which is drastically reducing the main recharge of the aquifer the guadalfeo river makes it likely there will be profound hydrogeological changes delimiting the extent of the saline wedge is therefore a fundamental step towards quantifying the effects of both the dam and the changes in soil use seawater saturated zones have a resistivity ranging from 0 5 to 5 m detrital sediments 8 400 m carbonates 80 300 m and schists from 2 to 60 m the current position of the saline wedge has been located at 100 200 m from the coastline indicating a healthy state for the aquifer areas with wide and narrow mixing zones have been noted and related to differences in the hydrogeological characteristics of the aquifer

the middle permian capitanian mass extinction on land and in the oceans abstract a middle permian mass extinction first discovered in 1994 has become known as the end guadalupian event in the literature however recent studies of foraminifera and brachiopod range truncations in conodont dated sections on the south china block have shown that the losses occur below this level in the middle of the capitanian stage extinctions were suffered by several other groups notably the corals whilst the mollusc record is more enigmatic a major bivalve crisis has been reported in some studies the giant alatoconchids being notable victims but not others gastropods were unaffected by the crisis whilst a roughly contemporaneous ammonoid mass extinction may have occurred in the early wuchiapingian a few million years after the main marine losses compilation of data from plant species in south china reveals a significant 24 loss suggesting that the capitanian crisis also occurred on land an intra capitanian extinction of 56 of plant species in north china block sequences may also have coincided with these losses correlation of these marine and terrestrial extinction events using the palaeomagnetic record provides two alternatives either turnover amongst plant species is contemporaneous with the marine extinction and the eruption of the emeishan flood basalt province in southwest china or plant losses post date the marine extinction and instead coincide with the waning phase of the igneous province current understanding of the major dinocephalian extinction suggests this event occurred during the preceding stage the wordian but future improvements in both sampling and dating this tetrapod crisis may reveal a synchronicity of plant animal and marine invertebrate extinctions the clear temporal link of the capitanian marine extinction with emeishan volcanism suggests that these flood basalt eruptions triggered the crisis a contemporaneous major negative c isotope excursion suggests that like many other mass extinction events methane release from hydrates may also be implicated however in the best dated chinese sections the main excursion is found to slightly post date the extinction which occurs at the end of an unusual and unexplained interval of exceptionally heavy 13c values other usual suspects for mass extinctions either lack geological and palaeontological evidence e g marine anoxia and global cooling or do not precisely correlate with the extinction e g major eustatic regression

high resolution hg chemostratigraphy a contribution to the distinction of chemical fingerprints of the deccan volcanism and cretaceous paleogene boundary impact event abstract there is a renewed interest in volcanism as the major trigger for dramatic climatic changes at the cretaceous paleogene transition ktb which were accompanied by a decrease in biodiversity and mass extinction we have used hg contents as proxy for volcanic activity at the classical localities of gubbio italy and stevns klint denmark where the ktb layer is easily recognizable and at a near complete succession exposed at the bajada del jaguel locality in the neuquen basin argentina these three localities display similar 13ccarb trends with markedly negative excursion at the ktb layer bulk rock oxygen isotopes yielded similar pathways across the ktb layers in these localities and if considered near primary the negative 18o excursion at the ktb in gubbio and bajada del jaguel suggest warming temperatures during this transition whereas the negative excursion immediately followed by positive one at stevns klint points to a cycle of warm followed by colder climate at stevns klint hg contents reach 250 ng g 1 within the ktb layer fiskeler member and 45 ng g 1 at 1 5 m above that while within the scaglia rossa formation at gubbio three hg peaks across the ktb are observed one of them within the ktb layer 5 3 ng g 1 hg shows several peaks across the ktb in the neuquen basin with up to 400 ng g 1 in the jaguel formation the phenomena that caused dramatic changes at the ktb probably expelled huge amounts of hg into the atmosphere as recorded by these high hg levels a co variation between hg and al2o3 in the studied sections suggest that hg is adsorbed onto clays hg concentrations and also hg isotopes are perhaps a powerful tool in the assessment of the role of volcanic activity during extreme climatic and biotic events and in assessing the role of meteorite impact versus volcanism as the predominant cause of past global catastrophes and mass extinction

a negative carbon isotope anomaly associated with the earliest lopingian late permian mass extinction abstract palaeozoic life was severely affected in a pair of mass extinction events at the beginning earliest lopingian 260 million years ago and the end 251 million years ago of the late permian however the biological and geochemical record of the earliest lopingian crisis remains poorly constrained we present analyses of strata in south china showing that a negative anomaly of stable carbon isotope ratios accompanied an abrupt extinction of marine faunas at the beginning of the late permian similar to patterns observed at the end permian and the end cretaceous 65 million years ago extinction events

aquifer boundaries explored by geoelectrical measurements in the coastal plain of yemen a case of equivalence until 216 vertical electrical schlumberger soundings were made little was known about the subsurface geology at the wadi surdud area in the coastal plain of the yemen arab republic these soundings provide information on the distribution of aquifers aquitards and impermeable rocks and the salinity of the groundwater a first qualitative interpretation of the geoelectrical sounding curves gives a general impression of the hydrogeologic setting and the aquifer boundaries however a more detailed quantitative interpretation shows that no single resistivity model completely satisfies all the hydrogeologic and geologic facts and theories basically two different models are possible in one the thickness of the aquifer is fixed in the other its resistivity is fixed several geologic and hydrogeologic hypotheses may be put forward to support each model varying from relying upon tectonic events and sedimentary depositional environments to influences of agriculture and water abstraction both models are

a dynamic explanation for the origin of the western mediterranean organic rich layers the eastern mediterranean sapropels are among the most intensively investigated phenomena in the paleoceanographic record but relatively little has been written regarding the origin of the equivalent of the sapropels in the western mediterranean the organic rich layers orls orls are recognized as sediment layers containing enhanced total organic carbon that extend throughout the deep basins of the western mediterranean and are associated with enhanced total barium concentration and a reduced diversity dysoxic but not anoxic benthic foraminiferal assemblage consequently it has been suggested that orls represent periods of enhanced productivity coupled with reduced deep ventilation presumably related to increased continental runoff in close analogy to the sapropels we demonstrate that despite their superficial similarity the timing of the deposition of the most recent orl in the alboran sea is different than that of the approximately coincident sapropel indicating that there are important differences between their modes of formation we go on to demonstrate through physical arguments that a likely explanation for the origin of the alboran orls lies in the response of the western mediterranean basin to a strong reduction in surface water density and a shoaling of the interface between intermediate and deep water during the deglacial period furthermore we provide evidence that deep convection had already slowed by the time of heinrich event 1 and explore this event as a potential agent for preconditioning deep convection collapse important differences between heinrich like and deglacial like influences are highlighted giving new insights into the response of the western mediterranean system to external forcing

the mid capitanian middle permian mass extinction and carbon isotope record of south china abstract conodont c isotope and fossil and facies data are presented for the capitanian middle permian mass extinction record seen in platform carbonates maokou and wuchiaping formations of south china where limestones interdigitate with the volcanic succession of the emeishan large igneous province the maokou formation provides an extinction record marked by the loss of keriothecal walled fusulinaceans and a turnover in calcareous algae in sections within the emeishan province this crisis occurs at the base of the oldest record of volcanism from the jinogondolella altudaensis conodont zone of mid capitanian age around the periphery of the emeishan province this extinction level lies within the upper part of the maokou formation at a level where platform carbonate deposition was frequently interrupted by thick volcanic ash depositional events the assemblages of the uppermost maokou formation are characterised by typical late permian taxa although these levels still lie within the middle permian guadalupian series disaster taxa such as earlandia and diplosphaerina are locally prolifically abundant in the aftermath of the mass extinction the crisis is particularly noteworthy amongst photosynthetic taxa such as calcareous algae and fusulinaceans that probably harboured photosymbionts therefore a kill mechanism involving cooling from explosive volcanism and potentially acid rain from sulphate aerosols appears appropriate a composite 13ccarb curve calibrated against a high resolution conodont biostratigraphy reveals a major intra capitanian negative excursion of 5 superimposed on typically heavy 4 5 middle permian values this curve can also be recognised in panthalassan seamount carbonates of japan although this requires reassignment of apparently upper permian limestones to the middle permian in both china and japan the capitanian mass extinction occurs during the early stage of this major intra capitanian negative excursion assuming typical platform carbonate accumulation rates the records of the maokou formation suggest 13ccarb values fell at 0 01 kyr suggesting a catastrophic origin such as gas hydrate destabilisation is unlikely although a volcanic source is possible

petrology of late paleozoic early mesozoic pyeongan group sandstones gohan area south korea and its provenance and tectonic implications abstract carboniferous to triassic strata of the pyeongan group crop out in the gohan area northeastern south korea these strata consist in ascending order of the hongjeom sadong gobangsan and nogam formations sandstones in these formations comprise three distinct framework mineral suites suite 1 sandstones hongjeom formation through the middle member of gobangsan formation are quartz and quartzose arenites wackes that contain abundant quartz little or no feldspar and few acid volcanic clasts heavy minerals are mainly tourmaline rutile and zircon suite 2 sandstones upper member of gobangsan formation are lithic arenites wackes characterized by moderate quartz content low amounts of feldspar and moderate to abundant volcanic clasts sphene is the predominant heavy mineral suite 3 sandstones nogam formation are feldspathic arenites wackes distinguished by low quartz content moderate to abundant feldspar and low amounts of acid volcanic clasts the heavy mineral assemblage of the nogam formation is characterized particularly by epidote and sphene feldspar poor suite 1 sandstones were derived from a source terrain rich in quartzite and quartzose sandstone abundant quartz and stable heavy minerals were supplied initially during late carboniferous time to a shallow marine shelf which changed gradually near the end of carboniferous time to a nonmarine paralic platform setting electron probe microanalysis shows that suite 1 tourmaline was derived originally from li poor granitoids pegmatites and ca poor aplite and metapsammite petrographic evidence demonstrates that the scarcity of feldspars in suite 1 sandstones is not the result of diagenetic intrastratal solution major changes in mineralogy from suite 1 into suite 2 and suite 3 sandstone indicate changes in provenance suite 2 sandstones were derived from diorite granodiorite acid volcanic rocks and possibly some metamorphic rocks which furnished feldspars and sphene the appearance of feldspars and volcanic rock fragments in these sandstones reflects orogenic changes and uplift resulting from incipient collision of the asian mainland and the honshu block of southwest japan compositionally immature suite 3 sandstones were derived mainly from granite granodiorite and granitic gneiss indicating continuing uplift these source rocks provided quartz k feldspar plagioclase epidote and sphene acid volcanic rocks supplied minor amounts of rock fragments

contributions of soot to 13c of organic matter in cretaceous lacustrine deposits gyeongsang basin korea implication for paleoenvironmental reconstructions abstract this study reports that soot carbon sc derived from biomass burning is an important constituent of total organic carbon toc 30 90 in two cretaceous lacustrine deposits middle albian jinju formation and early cenomanian banyaweol formation of the gyeongsang basin korea and that sc contributed significantly to the carbon isotope composition 13 c of the toc 13 c of the toc and 13 c of the sc corrected non sc organic matter range from 24 7 to 21 9 and 25 1 to 20 7 in the jinju formation and 24 7 to 23 0 and from 26 4 to 21 7 in the banyaweol formation respectively based on the 13 c values of coeval charcoal the calculated 13 c of the original plant material in the surrounding watershed of the paleo jinju lake ranged from 21 8 to 17 8 av 19 3 these values are considerably different from 13 c of vegetation av 24 3 estimated from sc the estimated 13 c values of non sc organic carbon are different from those of the toc by up to 3 5 either an enrichment or depletion across this value this discrepancy indicates that the presence of sc in sedimentary organic carbon affected carbon isotope composition of toc in the studied lacustrine deposits and led to increase uncertainty of interpretation of paleoenvironment of the watershed for improving the paleoenvironmental reconstructions by utilizing the 13 c values of toc in ancient lacustrine sediments a correction for the contribution of sc to toc needs to be considered

exchange through the strait of gibraltar to measure the exchange between the atlantic and mediterranean through the strait of gibraltar an array of current meter moorings was deployed for a year in the strait during 1985 1986 a novel aspect of these measurements is the inclusion of conductivity as well as temperature and pressure sensors on each current meter so that the salinity of the flows could be monitored continuously these salinity measurements determine the water mass characteristics of the flows crossing the sill they allow definition of the 37 psu isohaline as the interface between inflowing fresher atlantic water and outflowing saltier mediterranean water and they enable time series to be developed for the depth of this interface for the upper layer inflow and for the lower layer outflow from these measurements the time averaged outflow of mediterranean water is estimated to be 0 68sv 1sv 1 106m3s 1 and the outflow salinity transport defined to be the outflow times the salinity excess above a basic atlantic water salinity of 36 1 psu is estimated to be 1 50 103m3s 1 1sv 1psu 1 103m3s 1 equivalent to a net evaporation over the mediterranean basin of 52cm y 1 extrapolated measurements of the inflow from current meters generally deployed below 100m depth yield an estimate for the time averaged inflow of 0 93sv which is believed to be unrealistically high in view of the better measured outflow and net evaporation thus a more realistic estimate of the inflow is 0 72sv equal to the sum of the outflow and net evaporation as required by the mass budget for the mediterranean sea such estimates of the exchange are smaller by almost a factor of 2 than previous values for the exchange by lacombe and richez 1982 the exchange across the gibraltar sill is found to be due in nearly equal parts to the mean currents and to the tidal fluctuations the mean currents are smaller than had been expected reaching a peak value of only about 60 cm s 1 in the deep outflow over the sill the tidal exchange is due to a strong correlation over the tidal period between the depth of the interface and the strength of the inflowing currents for the m2 tide at the sill the amplitude of the interface depth is 51 m and the amplitude of the tidal currents is 1 2m s 1 furthermore the inflow and interface depth have similar phases as a consequence the upper layer is deep on the inflowing tide so that a large slug of atlantic water crosses the sill into the mediterranean on the outflowing tide the interface is shallow so that a large slug of mediterranean water crosses the sill into the atlantic similar processes occur for the s2 o1 and k1 tides though the amplitude are smaller in this manner tidal oscillations lead to a time averaged exchange of water masses across the gibraltar sill the inflow and outflow defined to be the instantaneous transports above and below the 37psu isohaline interface exhibit m2 tidal amplitudes of 2 3 sv and 1 3sv respectively thus the tides are large enough to reverse the mean upper layer inflow and lower layer outflow daily averaged inflow and outflow transports exhibit low frequency fluctuations with standard deviations of 0 37sv and 0 22sv respectively such low frequency fluctuations have been shown previously to be associated with barotropic flows through the strait of gibraltar compensating for sea level variations over the mediterranean due to atmospheric pressure fluctuations candela winant and bryden 1989 finally from these measurements there appear to be little fortnightly or annual period fluctuations in the exchange through the strait of gibraltar

mediterranean outflow water dynamics across the middle pleistocene transition based on a 1 3 million year benthic foraminiferal record off the portuguese margin abstract reconstruction of the mediterranean outflow water mow dynamics in the geologic past contributes to exploring its influence on the north atlantic ocean circulation and global climate the middle pleistocene transition mpt is one of the most important characteristics of quaternary climate change but until now research on the mow variability during this time interval has been limited to decipher the mow variability over the last 1 3 myr this work presents the first continuous and high resolution 2 kyr foraminiferal stable oxygen and carbon isotopes and benthic foraminiferal records from integrated ocean drilling program iodp site u1391 which was drilled off the portuguese margin in the northeast atlantic ocean and is currently bathed by the lower mow core based on spectral analysis results of the foraminiferal 18o record the mpt peaked from 0 9 to 0 7 ma the epibenthos group was previously found attached to elevated substrates only within the mow current and more abundant at higher current velocities so the relative abundance of the elevated epibenthos group was adopted as an indicator of mow strength in this study the mow indicator suggests that the mow strengthened during mis 1 mis 5 mis 7 mis 9 mis 11 mis 13 mis 15 mis 17 early mis 18 to late mis 19 mis 21 miss 23 25 miss 28 30 early mis 34 to mis 35 early mis 36 to late mis 37 and mis 40 with a 100 kyr cycle superimposed on the long term variability of the mow current the 41 kyr and 20 kyr cyclic fluctuations are also evident whereby the 41 kyr cycle is more significant the results of cross spectral analyses indicate that the 20 kyr cyclic variation in the mow intensity was drived by the precession forcing the 41 kyr cyclic variation in the pre mpt mow dynamics and the 100 kyr cyclic variation in the post mpt mow dynamics were strongly controlled by the earth s obliquity the variation in the abundance of the elevated epibenthos group was dominated by the 41 kyr cycle prior to the mpt and by the 100 kyr cycle after the mpt which suggested there was a mpt related shift in the mow dynamics benthic 13c record of the last 0 56 myr shows precessional 23 kyr and glacial interglacial 100 kyr cycles indicating cyclic variations in bottom water ventilation enhanced ventilation coincides with precession maxima and reduced ventilation with precession minima bottom water was well ventilated by mow during the interglacial periods and by gnaiw during the glacial periods and pooly ventilated during the glaical terminations

a 130 000 year record of levantine intermediate water flow variability in the corsica trough western mediterranean sea abstract sortable silt particle size data and stable isotope analyses from the corsica trough western mediterranean sea provide a continuous palaeoceanographic record of the inflow ventilation and vertical fluctuations of the levantine intermediate water liw in the northern tyrrhenian sea for the last 130 000 years the results presented herein reveal that climate changes drive the mediterranean intermediate circulation on milankovitch to millennial time scales intensified intermediate inflow and ventilation in the corsica trough occurred throughout the last glacial interval with a cold faster warm slower pattern existing between the dansgaard oeschger climatic oscillations including heinrich events and the liw variability by contrast a weak intermediate ventilation characterised the holocene and the last interglacial period especially during insolation maxima and the sapropel deposition in the eastern mediterranean this variability probably reflects the changes of the eastern mediterranean net evaporation as well as the propagation to the western mediterranean of the profound hydrographic adjustments of the levantine sea and adjacent areas to climate forcing the implications for the formation and ventilation of the western mediterranean deep water wmdw in the northwestern mediterranean basin as well as for mediterranean atlantic exchange through the strait of gibraltar are discussed

vertical density gradient in the eastern north atlantic during the last 30 000 years past changes in the density and momentum structure of oceanic circulation are an important aspect of changes in the atlantic meridional overturning circulation and consequently climate however very little is known about past changes in the vertical density structure of the ocean even very extensively studied systems such as the north atlantic here we exploit the physical controls on the settling depth of the dense mediterranean water plume derived from the strait of gibraltar to obtain the first robust observations based probabilistic reconstruction of the vertical density gradient in the eastern north atlantic during the last 30 000 years we find that this gradient was weakened by more than 50 relative to the present during the last glacial maximum and that changes in general are associated with reductions in amoc intensity however we find only a small change during heinrich event 1 relative to the last glacial maximum despite strong evidence that overturning was substantially altered this implies that millennial scale changes may not be reflected in vertical density structure of the ocean which may be limited to responses on an ocean overturning timescale or longer regardless our novel reconstruction of atlantic density structure can be used as the basis for a dynamical measure for validation of model based amoc reconstructions in addition our general approach is transferrable to other marginal sea outflow plumes to provide estimates of oceanic vertical density gradients in other locations

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

increased fire activity at the triassic jurassic boundary in greenland due to climate driven floral change an episode of climate warming 200 myr ago was associated with catastrophic environmental changes experimental and palaeontological data suggest that a climate driven shift to more flammable leaf shapes contributed to increased fire activity in east greenland at this time one of the largest mass extinctions of the past 600 million years myr occurred 200 myr ago at the triassic jurassic boundary the major floral and faunal turnovers1 have been linked to a marked increase in atmospheric carbon dioxide levels2 probably resulting from massive volcanism in the central atlantic magmatic province3 4 future climate change predictions suggest that fire activity may increase5 in part because higher global temperatures are thought to increase storminess6 7 here we use palaeontological reconstructions of the fossil flora from east greenland to assess forest flammability along with records of fossil charcoal preserved in the rocks to show that fire activity increased markedly across the triassic jurassic boundary we find a fivefold increase in the abundance of fossil charcoal in the earliest jurassic which we attribute to a climate driven shift from a prevalence of broad leaved taxa to a predominantly narrow leaved assemblage our fire calorimetry experiments show that narrow leaf morphologies are more flammable than broad leaved morphologies we suggest that the warming associated with increased atmospheric carbon dioxide levels favoured a dominance of narrow leaved plants which coupled with more frequent lightening strikes led to an increase in fire activity at the triassic jurassic boundary

evidence from the high latitude north atlantic for variations in antarctic intermediate water flow during the last deglaciation we present evidence that the characteristic chemical signature based on coupled benthic foraminiferal cd ca and d13c of antarctic intermediate waters aaiw penetrated throughout the intermediate depths of the atlantic basin to the high latitude north atlantic during the abrupt cooling events of the last deglaciation heinrich 1 and the younger dryas aaiw may play the dynamic counterpart to the bipolar seesaw when near freezing salty bottom waters from the antarctic aabw sluggishly ventilate the deep ocean our data reinforce the concept that interglacial circulation is stabilized by salinity feedbacks between salty northern sourced deep waters nadw and fresh southern sourced waters aabw and aaiw further the glacial ocean may be susceptible to the more finely balanced relative densities of nadw and aaiw due to either freshwater input or a reversal of the salinity gradient such that the ocean is poised for nadw collapse via a negative salinity feedback the unstable climate of the glacial period and its termination may arise from the closer competition for ubiquity at intermediate depths between northern and southern sourced intermediate waters

evidence of abrupt changes in western mediterranean deep water circulation during the last 50kyr a high resolution marine record from the balearic sea abstract the images core md99 2343 recovered from a sediment drift north of the island of minorca in the north western mediterranean sea holds a high resolution sequence that is perfectly suited to study the oscillations of the overturning system of the western mediterranean deep water wmdw detailed analysis of grain size and bulk geochemical composition reveals the sensitivity of this region to climate changes at both orbital and centennial millennial temporal scales during the last 50 kyr the dominant orbital pattern in the k al record indicates that sediment supply to the basin was controlled by the insolation evolution at 40 n which forced changes in the fluvial regime with more efficient sediment transport during insolation maxima this orbital control also modulated the long term pattern of the wmdw intensity as illustrated by the silt clay ratio however deep convection was particularly sensitive to climatic changes at shorter time scales i e to centennial millennial glacial and holocene oscillations that are well documented by all the paleocurrent intensity proxies si al ti al and silt clay ratios benthic isotopic records 13c and 18o show a dansgaard oeschger d o pattern of variability of wmdw properties which can be associated with changing intensities of the deep currents system the most prominent reduction on the wmdw overturning was caused by the post glacial sea level rise three main scenarios of wmdw overturning are revealed a strong mode during d o stadials a weak mode during d o interstadials and an intermediate mode during cooling transitions in addition d o stadials associated with heinrich events hes have a very distinct signature as the strong mode of circulation typical for the other d o stadials was never reached during he due to the surface freshening induced by the inflowing polar waters consequently the wmdw overturning system oscillated around the intermediate mode of circulation during he though surface conditions were more stable during the holocene the wmdw overturning cell still reacted synchronously to short lived events as shown by increments in the planktonic 18o record triggering quick reinforcements of the deep water circulation overall these results highlight the sensitivity of the wmdw to rapid climate change which in the recent past were likely induced by oceanographic and atmospheric reorganizations in the north atlantic region

carbon isotope composition of lower cretaceous fossil wood ocean atmosphere chemistry and relation to sea level change the carbon isotope composition of fossil wood fragments collected through a biostratigraphically well constructed aptian lower cretaceous shallow marine siliciclastic succession on the isle of wight southern britain shows distinct variations with time the results indicate that the stratigraphic signature of delta sup 13 c sub wood through the aptian was influenced primarily by fluctuations in the isotopic composition of co sub 2 in the global ocean atmosphere system as registered in marine carbonates elsewhere and was not governed by local paleoenvironmental and or paleoecological factors negative and positive excursions in delta sup 13 c sub wood through the lower aptian occur in phase with inferred transgressions and regressions respectively a pattern that contrasts with that observed in many previous studies for different time intervals the relationship between delta sup 13 c variations and relative sea level change is tentatively interpreted as a response to various climatic and eustatic factors relating to rapid sea floor spreading thermal uplift of ocean floor emplacement of plateaus volcanic co sub 2 emissions weathering and sedimentary rate

temperature and salinity variations of mediterranean sea surface waters over the last 16 000 years from records of planktonic stable oxygen isotopes and alkenone unsaturation ratios alkenone unsaturation ratios and planktonic d18o records from sediment cores of the alboran ionian and levantine basins in the mediterranean sea show pronounced variations in paleo temperatures and salinities of surface waters over the last 16 000 years average sea surface temperatures ssts are low during the last glacial averages prior to 13 000 years 11 15 c vary rapidly at the beginning of the holocene and increase to 17 18 ca t all sites during s1 formation dated between 9500 and 6600 calendar years the modern temperature gradient 2 3 c between the mediterranean sub basins is maintained during formation of sapropel s1 in the eastern mediterranean sea after s1 ssts have remained uniform in the alboran sea at 18 c and have fluctuated around 20 c in the ionian and levantine basin sites the d18o of planktonic foraminifer calcite decreases by 2 from the late glacial to s1 sediments in the ionian basin and by 2 8 in the levantine basin in the alboran sea the decrease is 1 7 of the 2 8 decrease in the levantine basin the evect of global ice volume accounts for a maximum of 1 05 and the temperature increase explains only a maximum of 1 3 the remainder is attributed to salinity changes we use the temperature and salinity estimates to calculate seawater density changes they indicate that a reversal of water mass circulation is not a likely explanation for increased carbon burial during s1 time instead it appears that intermediate and deep water formation may have shifted to the ionian sea approximately 2000 years before onset of s1 deposition because surface waters were as cold but saltier than surface water in the levantine basin during the younger dryas sapropel s1 began to form at the same time when a significant density decrease also occurred in the ionian sea 2000 elsevier science b v all rights reserved

volcanism mass extinction and carbon isotope fluctuations in the middle permian of china the 260 million year old emeishan volcanic province of southwest china overlies and is interbedded with middle permian carbonates that contain a record of the guadalupian mass extinction sections in the region thus provide an opportunity to directly monitor the relative timing of extinction and volcanism within the same locations these show that the onset of volcanism was marked by both large phreatomagmatic eruptions and extinctions amongst fusulinacean foraminifers and calcareous algae the temporal coincidence of these two phenomena supports the idea of a cause and effect relationship the crisis predates the onset of a major negative carbon isotope excursion that points to subsequent severe disturbance of the ocean atmosphere carbon cycle

fingerprinting northeast atlantic water masses using neodymium isotopes dissolved neodymium nd isotopic composition expressed as end has been analysed for 82 seawater samples collected from 13 stations stretching from the alboran sea to the iceland basin the distribution of the end values of water masses was thus investigated for the first time along the western european margin in order to explore whether the water masses flowing in the eastern subpolar and subtropical atlantic reveal distinct isotopic patterns the modified atlantic water maw in the alboran sea displays end values between 9 2 0 2 and 8 9 0 2 that are significantly more radiogenic than those reported in previous studies 10 8 0 2 to 9 7 0 2 suggesting temporal variations in the nd isotopic composition of the water that enters the mediterranean sea from the strait of gibraltar the end value of the underlying modified winter intermediate water wiw has been established for the first time 9 8 0 3 and is compatible with a nd signature acquired from the sinking of maw in the northwestern mediterranean sea within the gulf of cadiz southern mediterranean sea water msw 10 6 0 2 differs slightly from the northern msw 9 9 0 4 owing to a significant contribution of modified east antarctic intermediate water eaaiw 10 9 0 2 in the northeast atlantic the north atlantic current surface water located in the inter gyre region north of 46 n displays end values of between 14 0 0 3 and 15 1 0 3 reflecting the subpolar gyre signature along the western european margin end values of surface water decrease toward the north from 10 4 1 6 to 13 7 1 0 in agreement with the gradual mixing between subtropical and subpolar water at intermediate depth end values decrease from 9 9 0 4 within the gulf of cadiz to 12 1 0 3 within the porcupine seabight indicating a strong dilution of the msw with subpolar water within the rockall trough and the iceland basin the more negative end values at mid depth 13 5 0 3 indicate that the msw has no influence even during periods of low nao index water masses deeper than 1200 m in the northeast atlantic are clearly influenced by the less radiogenic labrador sea water lsw 13 2 0 3 and 14 5 0 3 that mixes locally end between 10 3 0 2 and 11 3 0 3 in the iceland basin with the iceland scotland overflow water isow

late glacial to holocene history of the mediterranean outflow evidence from benthic foraminiferal assemblages and stable isotopes at the portuguese margin records of benthic foraminiferal assemblage variations and benthic 13c along 12 sediment cores from the western iberian margin between 36 and 42 n at water depths from 820 to 3580 m are used to monitor fluctuations of the mediterranean outflow water mow during the past 30 ka the chronostratigraphy of the cores is based on planktonic 18o records 14c ams dating and the recognition of heinrich events h1 through h4 increased abundances of suspension feeding benthic foraminifers denoted as epibenthos group closely match areas where the recent mow core layers impinge on the continental slope at 800 and 1300 m water depth and near bottom current velocities are enhanced elevated epibenthos group abundances increased benthic 13c and sedimentological evidence for winnowing and erosion are found in glacial sections up to the earliest termination i in cores at water depths between 1600 and 2200 m off southern portugal the combined evidence reveals enhanced current activity at these depths due to a deep glacial mow the mow advection at the portuguese margin during the last glacial was about 700 m deeper than today conceivably forced by increased mow density due to higher salinity and colder temperatures of mediterranean waters the deep mow current gradually decreased in strength and shoaled to 1300 m water depth during the termination and early holocene a shallow mow core layer became active with the onset of termination i at depths between 600 and 1000 m both the shallow and deep mow current culminated during the younger dryas period the present flow pattern with two mow core layers centred at 800 and 1300 m water depth was established between 7 5 and 5 5 ka

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

the sines contourite depositional system along the sw portuguese margin onset evolution and conceptual implications abstract the sines contourite depositional system located in the southwest portuguese margin is a central segment of the iberian contourite depositional complex built under the influence of the mediterranean outflow water mow this work presents the onset and evolution of this system using multibeam bathymetry multichannel seismic reflection lines sediment cores and well data six seismic units of late miocene through holocene age have been identified which defined three evolutionary stages for drift construction a an onset and initial stage from the latest miocene to the late pliocene 5 33 2 5 ma where a sheeted drift was built under a weak flowing mow b a growing stage from the early to middle quaternary 2 5 0 7 ma characterized by the deposition of a mounded drift in the south and a sheeted drift in the north which is correlated with a strengthening of the mow and c a maintenance stage between the middle pleistocene and holocene 0 7 ma present where the modern depositional and erosional contourite features developed associated with three intensification periods of the mow at 0 7 ma 0 4 ma and 20 ka the development of the sines contourite depositional system was constrained in the long term by seafloor paleomorphologies inherited from the mesozoic rifting phases of the southwest portuguese margin the nnw sse horsts and grabens built during the mesozoic rifting provided accommodation for drift growth with limited lateral migration and locally enhanced the alongslope bottom current in short term environmental climate and sea level fluctuations modulated changes in bottom current density and intensity determining sedimentary cycles in the depositional record especially during the quaternary our findings emphasize the occurrence of three main plastered morphologies throughout the seismic record which were compared with other plastered drifts in different continental margins to establish a conceptual model

new constraints on the pb and nd isotopic evolution of ne atlantic water masses 1 time series of lead pb and neodymium nd isotope compositions were measured on three ferromanganese crusts recording the evolution of ne atlantic water masses over the past 15 ma the crusts are distributed along a depth profile 700 4600 m comprising the present day depths of mediterranean outflow water and north east atlantic deep water a pronounced increase of the 206pb 204pb in the two deeper crusts starting at 4 ma and a decrease in 143nd 144nd in all three crusts took place between 6 4 ma and the present these patterns are similar to isotope time series in the western north atlantic basin and are consistent with efficient mixing between the two basins however the changes occurred 1 3 ma earlier in the eastern basin indicating that the northeastern atlantic led the major change in pb and nd isotope composition probably due to a direct supply of labrador seawater via a northern route the pb isotope evolution during the pliocene pleistocene can generally be explained by mixing between two end members corresponding to mediterranean outflow water and north east atlantic deep water but external sources such as saharan dust are likely to have played a role as well the pb isotope composition of the shallowest crust that grew within the present day mediterranean outflow water does not show significant pb isotope changes indicating that it was controlled by the same pb sources throughout the past 15 ma

glacial to interglacial changes in the settling depth of the mediterranean outflow plume we present micropalaeontological and grain size records for a set of sediment cores from the gulf of cadiz southwest spain that reflect changes in the position and strength of the mediterranean outflow mo current the cores sample a sediment drift the gil eanes drift that is positioned lower on the slope in the gulf of cadiz than the position of the main current today the data indicate that the drift is of glacial age and that the glacial mo current was positioned lower on the slope than today but also that it was active over a considerably reduced area of the slope we argue that this observation is consistent with physical constraints on the gibraltar exchange and on the likely settling and spreading behavior of the mo plume along the iberian margin under glacial environmental and sea level conditions the deeper settling of the mo is likely to have influenced the formation of glacial north atlantic intermediate water and also may have exerted indirect influence on the formation of glacial north atlantic deep water

paleoceanography of the atlantic mediterranean exchange overview and first quantitative assessment of climatic forcing 1 the mediterranean sea provides a major route for heat and freshwater loss from the north atlantic and thus is an important cause of the high density of atlantic waters in addition to the traditional view that loss of fresh water via the mediterranean enhances the general salinity of the north atlantic and the interior of the eastern north atlantic in particular it should be noted that mediterranean water outflowing at gibraltar is in fact cooler than compensating inflowing water the consequence is that the mediterranean is also a region of heat loss from the atlantic and contributes to its large scale cooling uniquely this system can be understood physically via the constraints placed on it by a single hydraulic structure the gibraltar exchange here we review the existing knowledge about the physical structure of the gibraltar exchange today and the evidential basis for arguments that it has been different in the past using a series of quantitative experiments we then test prevailing concepts regarding the potential causes of these past changes we find that 1 changes in the vertical position of the plume of mediterranean water in the atlantic are controlled by the vertical density structure of the atlantic 2 a prominent early holocene contourite gap within the gulf of cadiz is a response to reduced buoyancy loss in the eastern mediterranean during the time of sapropel 1 deposition 3 changes in buoyancy loss from the mediterranean during mis3 caused changes in the bottom velocity field in the gulf of cadiz but we note that the likely cause is reduced freshwater loss and not enhanced heat loss and 4 strong exchange at gibraltar during atlantic freshening phases implies that the gibraltar exchange provides a strong negative feedback to reduced atlantic meridional overturning given the very counterintuitive way in which the strait of gibraltar system behaves we recommend that without quantitative supporting work qualitative interpretations of how the system has responded to past external forcing are unlikely to be robust

promotion of meridional overturning by mediterranean derived salt during the last deglaciation we demonstrate that changes in the behavior of the mediterranean outflow water mow prior to and through the last deglaciation played an important role in promoting meridional overturning circulation moc estimation of past mow salt and heat fluxes indicates that they gradually increased through the last deglaciation between 17 5 and 14 6 thousand years ago ka b p where b p references year 1950 net evaporation from the mediterranean exported sufficient fresh water from the north atlantic catchment to cause an average salinity increase of 0 5 psu throughout the upper 2000 m of the entire north atlantic to the north of 25

detrital modes of the pyeongan supergroup late carboniferous early triassic sandstones in the samcheog coalfield korea implications for provenance and tectonic setting abstract medium to coarse sandstones of the carboniferous to early triassic pyeongan supergroup in the samcheog coalfield korea were studied to infer the provenance and tectonic settings of the source areas sandstone detrital modes change upwards stratigraphically sandstone types from the manhang to dosagog formations low to middle in the sequence are quartzarenite and sublitharenite to litharenite whereas sandstones of the gohan and donggo formations high in the sequence are feldspathic litharenite and arkose respectively using various ternary diagrams the provenance of the manhang to gohan formations is suggested to be a recycled orogen setting some gohan formation sandstones plot within the arc related setting field and the donggo formation sandstones plot within both continental block and recycled orogen fields results of quartz grain petrography are consistent with those of detrital modes quartz in sandstones of all units except the donggo formation indicates derivation from low rank metamorphic sources quartz in donggo sandstones was derived from medium to high rank metamorphic and plutonic source rocks considering the sandstone composition and palaeocurrent data the pyeongan supergroup probably was deposited in a molasse foreland basin and was derived from a synbasinal orogenic belt probably the akiyoshi orogen located in southwest japan

a review of the physical oceanography of the mediterranean outflow abstract the physical oceanography of the mediterranean sea is reviewed with particular emphasis on the mediterranean outflow in the gulf of cadiz in this region the dense mediterranean water forms a high velocity bottom current that interacts strongly with the sea floor the major energy source for the plume comes from the release of potential energy as the plume descends the continental slope and the major energy sink is work against bottom stress which is as large as 4 pa where the plume begins to descend the continental slope in this region the current makes a nearly inertial turn that would otherwise appear to be steered by the underlying topography the mediterranean plume entrains the overlying north atlantic central water and thereby loses much of its density anomaly the mixed mediterranean water becomes neutrally buoyant in the lower portion of the north atlantic thermocline near cape st vincent there are then two preferred transport modes having somewhat different temperature and salinity whose distinct characteristics can be found far into the open north atlantic the temperature salinity and volume of the mediterranean water in the strait of gibraltar and in the gulf of cadiz appear to be roughly constant since modern measurements have been made the estimated westward transport of mediterranean water has gone down considerably as direct measurement techniques have been applied a recent estimate is that the westward transport of pure mediterranean water is only about a half a sv 1 sv 106 m3 s 1 the transport of mixed mediterranean water in the western gulf of cadiz is larger by about a factor of three or four because of the entrainment of north atlantic water

detrital input productivity fluctuations and water mass circulation in the westernmost mediterranean sea since the last glacial maximum 1 by presenting sea surface temperatures planktonic oxygen isotope profiles and bulk geochemical composition of core sediments we offer a multiparameter reconstruction of western mediterranean oceanography from the last glacial maximum until the middle holocene 20 000 5000 cal years b p sediments from ocean drilling program site 975 in the algero balearic basin have been compared with three alboran basin cores ttr 300g ttr 302g and ttr 304g all of them investigated at high resolution this multiproxy approach has allowed two different modes of circulation to be recognized 1 during the lgm and from 8 0 cal ka b p onward no surface gradient in 18og bulloides is found associated with low productivity in close analogy to modern conditions 2 during the bolling allerod and early holocene significant surface isotopic gradients are found with periods probably indicating an unstable water column associated with enhanced productivity and low bottom oxygen conditions the close synchrony between the occurrence of the surface isotopic offset and organic rich layer formation implicates that the origin of these features is linked probably via shoaling of the regional thermohaline circulation paleo ssts derived from planktonic foraminifer assemblages indicate abrupt changes in surface conditions during the analyzed time interval fluctuations in marine productivity based on ba and total organic carbon are related to water column stability and atmospheric conditions a sharp warming and 18og bulloides excursion at the end of the younger dryas is probably linked to glacial meltwater influence the riverine input has been reconstructed using the mg al ratio and mg al peaks during arid periods greenland stadial 2a and younger dryas related to bypass margin processes

a digital linear filter for resistivity sounding with a generalized electrode array this paper presents a digital linear filter which maps composite resistivity transforms to apparent resistivities for any four electrode array over a horizontally layered earth a filter is provided for each of three sampling rates the choice of filter will depend on resistivity contrasts and computational facilities two methods of filter design are compared the wiener hopf least squares method is preferable for low sampling rate filters the fourier transform method is more successful in producing a filter with a high sampling rate which can handle resistivity contrasts of 100 000 1

an improved ert approach for the investigation of subsurface structures the joint use of multiple geophysical data types has been proven to be a powerful tool to both improve subsurface imaging and help in the interpretation process the main goal of this paper is to develop a multi geophysical approach for subsurface experimental investigations in which seismic data are used to improve electrical resistivity tomography quality the basic philosophy of the method is that seismic travel time data will be used to construct the prior model for the resistivity inversion synthetic data were employed to demonstrate the improvements enabled by the use of this strategy afterwards the scheme was applied successfully on field data from northwestern china the outcomes reveal that the multi geophysical approach improves the interpretation of the subsurface over a single source