seawater ph pco2 and co2 3 variations in the caribbean sea over the last 130 kyr a boron isotope and b ca study of planktic foraminifera abstract here a new analytical methodology is described for measuring the isotopic composition of boron in foraminifera using multicollector inductively coupled plasma mass spectrometry mc icpms this new approach is fast 10 samples analysed in duplicate per analytical session and accurate to better than 0 25 at 95 confidence with acceptable sample size requirements 1 3 mg of carbonate a core top calibration of several common planktic and two benthic species from geographically widespread localities shows a very close agreement between the isotopic composition measured by mc icpms and the isotopic composition of b oh 4 in seawater as predicted using the recently measured isotopic equilibrium factor of 1 0272 at the depth of habitat a down core and core top investigation of boron concentration b ca ratio shows that the partition coefficient is influenced by co2 3 complicating the application of this proxy nevertheless it is demonstrated that these two proxies can be used to fully constrain the carbonate system of surface water in the caribbean sea odp site 999a over the last 130 kyr this reconstruction shows that during much of the holocene and the last interglacial period surface water at site 999a was in equilibrium with the atmosphere with respect to co2 during the intervening colder periods although the surface water pco2 was lower than the holocene it was a minor to significant source of co2 to the atmosphere possibly due to either an expansion of the eastern equatorial atlantic upwelling zone or a more local expansion of coastal upwelling in the southern caribbean such reorganisation of the oceanic carbonate system in favour of a larger source of co2 to the atmosphere from the equatorial ocean may require mechanisms responsible for lowering atmospheric co2 during glacial periods to be more efficient than previously supposed

sea level estimates during the last deglaciation based on δ18o and accelerator mass spectrometry 14c ages measured in globigerina bulloides coupled measurements of 18o and accelerator mass spectrometry ams 14c in a particular species of planktonic foraminifera may be used to calculate sea level estimates for the last deglaciation of critical importance for this type of study is a knowledge of the seasonality of foraminiferal growth which can be provided by 18o measurements of modern shells core tops plankton tows isotopic 18o ams 14c dating and faunal records transfer function sea surface temperature were obtained from two cores in the north atlantic at about 37 n the locations were chosen to obtain high sedimentation rate records removed from the major ice melt discharge areas of the last deglaciation based upon globigerina bulloides data four 18o based sea level estimates were calculated 67 7 m at 12 200 yr b p and 24 8 m at about 8200 yr b p for core su 81 18 83 10 m at 12 200 yr b p and 13 11 m at about 8500 yr b p for core su 81 14 using a second working hypothesis concerning the seasonability of g bulloides growth it is suggested that the sea level rose by about 40 m during the millennium which followed 14 500 yr b p

changes in biological productivity along the northwest african margin over the past 20 000 years the intertropical convergence zone and the african monsoon system are highly sensitive to climate forcing at orbital and millennial timescales both systems influence the strength and direction of the trade winds along northwest africa and thus directly impact coastal upwelling sediment cores from the northwest african margin record upwelling related changes in biological productivity connected to changes in regional and hemispheric climate we present records of 230th normalized biogenic opal and corg fluxes using a meridional transect of four cores from 19 n 31 n along the northwest african margin to examine changes in paleoproductivity since the last glacial maximum we find large changes in biogenic fluxes synchronous with changes in eolian fluxes calculated using end member modeling suggesting that paleoproductivity and dust fluxes were strongly coupled likely linked by changes in wind strength opal and corg fluxes increase at all sites during heinrich stadial 1 and the younger dryas consistent with an overall intensification of the trade winds and changes in the meridional flux gradient indicate a southward wind shift at these times biogenic fluxes were lowest and the meridional flux gradients were weakest during the african humid period when the monsoon was invigorated due to precessional changes with greater rainfall and weaker trade winds over northwest africa these results expand the spatial coverage of previous paleoproxy studies showing similar changes and they provide support for modeling studies showing changes in wind strength and direction consistent with increased upwelling during abrupt coolings and decreased upwelling during the african humid period

itrf2014 a new release of the international terrestrial reference frame modeling nonlinear station motions for the first time in the international terrestrial reference frame itrf history the itrf2014 is generated with an enhanced modeling of nonlinear station motions including seasonal annual and semiannual signals of station positions and postseismic deformation for sites that were subject to major earthquakes using the full observation history of the four space geodetic techniques very long baseline interferometry vlbi satellite laser ranging slr global navigation satellite systems gnss and doppler orbitography and radiopositioning integrated by satellite doris the corresponding international services provided reprocessed time series weekly from slr and doris daily from gnss and 24 h session wise from vlbi of station positions and daily earth orientation parameters itrf2014 is demonstrated to be superior to past itrf releases as it precisely models the actual station trajectories leading to a more robust secular frame and site velocities the itrf2014 long term origin coincides with the earth system center of mass as sensed by slr observations collected on the two lageos satellites over the time span between 1993 0 and 2015 0 the estimated accuracy of the itrf2014 origin as reflected by the level of agreement with the itrf2008 both origins are defined by slr is at the level of less than 3 mm at epoch 2010 0 and less than 0 2 mm yr in time evolution the itrf2014 scale is defined by the arithmetic average of the implicit scales of slr and vlbi solutions as obtained by the stacking of their respective time series the resulting scale and scale rate differences between the two solutions are 1 37 0 10 ppb at epoch 2010 0 and 0 02 0 02 ppb yr while the postseismic deformation models were estimated using gnss gps data the resulting parametric models at earthquake colocation sites were applied to the station position time series of the three other techniques showing a very high level of consistency which enforces more the link between techniques within the itrf2014 frame the users should be aware that the postseismic deformation models are part of the itrf2014 products unlike the annual and semiannual signals which were estimated internally with the only purpose of enhancing the velocity field estimation of the secular frame

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

thorium 230 profiling in deep sea sediments high resolution records of flux and dissolution of carbonate in the equatorial atlantic during the last 24 000 years variations in carbonate flux and dissolution which occurred in the equatorial atlantic during the last 24 000 years have been estimated by a new approach that allows the point by point determination of paleofluxes to the seafloor an unprecedented time resolution can thus be obtained which allows sequencing of the relatively rapid events occurring during deglaciation the method is based on observations that the flux of unsupported 230th into deep sea sediments is nearly independent of the total mass flux and is close to the production rate thus excess 230th activity in sediments can be used as a reference against which fluxes of other sedimentary components can be estimated the study was conducted at two sites ceara rise western equatorial atlantic and sierra leone rise eastern equatorial atlantic in cores raised from three different depths at each site from measurements of 230th and caco3 changes in carbonate flux with time and depth were obtained a rapid increase in carbonate production starting at the onset of deglaciation was found in both areas this event may have important implications for the postglacial increase in atmospheric co2 by increasing the global carbonate carbon to organic carbon rain ratio and decreasing the alkalinity of surface waters and possibly the north atlantic deep water increased carbonate dissolution occurred in the two regions during deglaciation followed by a minimum during mid holocene and renewed intensification of dissolution in late holocene during the last 16 000 years carbonate dissolution was consistently more pronounced in the western than in the eastern basin reflecting the influence of antarctic bottom water in the west this trend was reversed during stage 2 possibly due to the accumulation of metabolic co2 below the level of the romanche fracture zone in the eastern basin

younger dryas style cooling events at glacial terminations i vi at odp site 658 associated benthic δ13c anomalies constrain meltwater hypothesis high resolution planktonic and epibenthic stable isotope records from ocean drilling program site 658 off northwest africa provide a basis for a detailed study of glacial terminations i vi during the last 650 000 years the duration of the terminations was about one half to one quarter of an orbital precession cycle 5800 10 700 years when its amplitude was high at low amplitudes the terminations lasted longer than half an obliquity cycle 29 000 years marked climatic rebounds similar to the younger dryas each with a duration of 1000 2500 years subdivided all six terminations into distinct steps a b and c important parts of the deglacial steps were as brief as 700 1000 years the speed of climatic change suggests that special associations existed between orbital forcing and inherent instability of the ice sheets in harmony with published models the more rapid pulses of glacial meltwater incursions to the northern north atlantic led to one or more brief short term shut downs of north atlantic deep water formation this process is reflected by pronounced benthic 13c minima that precisely coincide in most cases with the end of the 18o deglaciation steps and immediately terminate with succeeding younger dryas style cooling events thus we conclude that the rebounds resulted from a short term antecedent estuarine circulation regime in the north atlantic except for the younger dryas itself which succeeded the allerod with its well ventilated atlantic deepwater circulation and hence continues to be an enigma

kinematics of the western africa eurasia plate boundary from focal mechanisms and gps data summary the western mediterranean displays a complex pattern of crustal deformation distributed along tectonically active belts developed in the framework of slow oblique plate convergence we used earthquake and global positioning system gps data to study the present day kinematics and tectonics of the africa eurasia plate boundary in this region crustal seismicity and focal mechanisms analysed in terms of seismic moment release and seismic deformation outline the geometry of major seismic belts and characterize their tectonics and kinematics continuous gps data have been analysed to determine euler vectors for the nubian and eurasian plates and to provide the global frame for a new mediterranean gps velocity field obtained by merging continuous and campaign observations collected in the 1991 2005 time span gps velocities and displacements predicted by the nubia eurasia rotation pole provide estimates of the deformation accommodated across the tectonically active belts the rather simple deformation occurring in the atlantic region characterized by extension about perpendicular to the middle atlantic and terceira ridges and right lateral motion along the gloria transform fault turns into a complex pattern of deformation occurring along broader seismic belts where continental lithosphere is involved our analysis reveals a more complex fragmentation of the plate boundary than previously proposed the roughly e w trending mainly compressive segments i e southwestern iberia northern algeria and southern tyrrhenian where plate convergence is largely accomodated across rather localized deformation zones and partially transferred northward to the adjacent domains i e the algero balearic and tyrrhenian basins are interrupted by regions of more distributed deformation i e the rif alboran betics tunisia libya and eastern sicily or limited seismicity i e the strait of sicily which are characterized by less homogeneous tectonics regimes mainly transcurrent to extensional in correspondence of the observed breaks tectonic structures with different orientation interfere and we find belts with only limited deformation i e the high and middle atlas the tunisian atlas and the offshore tunisia libya belt that extends from the plate boundary into the nubian plate along pre existing tectonic lineaments our analysis suggest that the sicilian pelagian domain is moving independently from nubia according to the presence of a right lateral and extensional decoupling zone corresponding to the tunisia libya and strait of sicily deformation zone despite the space variability of active tectonic regimes plate convergence still governs most of the seismotectonic and kinematic setting up to the central aeolian region in general local complexities derive from pre existing structural features inherited from the tectonic evolution of the mediterranean region on the contrary along calabria and the apennines the contribution of the subducted ionian oceanic lithosphere and the occurrence of microplates i e adria appear to substantially modify both tectonics and kinematics finally gps data across the gibraltar arc and the tyrrhenian calabria domain support the hypothesis that slab rollback in these regions is mostly slowed down or stopped

assessment of geochemical and micropaleontological sedimentary parameters as proxies of surface water properties in the canary islands region abstract the canary islands region occupies a key position with respect to biogeochemical cycles with the zonal transition from oligotrophic to nutrient rich waters and the contribution of saharan dust to the particle flux we present the distribution of geochemical proxies toc carbonate 15n 13corg c n ratio and micropaleontological parameters diatoms dinoflagellates foraminifera pteropods in 80 surface sediment samples in order to characterise the influence of coastally upwelled water on the domain of the subtropical gyre results of the surface sediment analyses confirmed the high biomass gradient from the coast to the open ocean inferred from satellite data of surface chlorophyll or sst the distribution of total dinoflagellate cysts the planktic foraminifera species globigerina bulloides the diatom resting spore chaetoceros spp and toc concentration coincided well with the areas of strong filament production off cape ghir and cape yubi the warm water planktic foraminifera globigerinoides ruber white the diatom nitzschia spp and the 15n values showed the opposite trend with high values in the open ocean factor analyses on the planktic foraminifera species distribution indicated three major assemblages in the canary islands region that represent the present surface water conditions from the upwelling influenced region via a mixing area towards the subtropical gyre

unchanged nitrogen isotopic composition of organic matter in the south china sea during the last climatic cycle global implications the 15n of surface and down core sediments spanning the last 20 200 kyr from the entire south china sea scs ranges only from 3 0 to 6 5 with no correlation with discernible paleoclimatic oceanographic changes detailed profiles of the uppermost sediment column including fluff samples indicate a minor diagenetic overprint of 0 3 1 2 at the sediment water interface the absence of any correlation with reconstructed glacial interglacial changes in primary production terrigenous input and or sea level related basin configuration is attributed to a complete consumption of nitrate during primary production in this marginal basin during at least the last 140 000 years this in turn implies that the 15n of the nitrate used during primary production remained approximately constant during the last climatic cycle the proposed scenario infers an unchanged nitrogen isotopic composition of the western pacific subsurface nitrate between glacial and interglacial stages as well as during terminations and thus constrains proposed changes in the oceanic n inventory

sedimentary nitrogen isotopic ratio as a recorder for surface ocean nitrate utilization in two contrasting regions of the ocean the equatorial pacific and the southern ocean the 15n of core top sediments were strongly related to no3 in surface waters with distance from the equator in the equatorial pacific 15n increased from 7 to 16 as no3 decreased from 8 m to 0 1 m going from 60 to 30 s in the se indian ocean core top 15n increased from 5 to 11 as surface no3 decreased from 25 m to 0 1 m these results are strong evidence that sedimentary 15n in these regions is recording the increasing isotopic enrichment of near surface no3 with its depletion by phytoplankton in the case of the equatorial pacific 15n values for sinking particles collected at 150 m matched well the core top sediment values demonstrating little diagenetic alteration of the near surface generated isotopic signal these equatorial pacific data sets have variations with near surface no3 consistent with rayleigh fractionation kinetics for a fractionation factor u of 2 5 this value is substantially lower than previously found for temperate or polar regions perhaps as a result of differences in phytoplankton species assemblage or growth condition in the southern ocean south of the polar front comparison of 15n values for opal rich sediments south and sinking particles indicates an apparent 5 diagenetic enrichment relative to the surface generated signal that requires further investigation this exception aside our observations show that the surface water relationship of increasing 15n with increasing no3 depletion is generally transmitted to and preserved in the sediments an important requirement for further development and application of this important paleoceanographic tool

orbital forcing of dust supply to the north canary basin over the last 250kyr abstract the canary basin lies in a region of strong interaction between the atmospheric and ocean circulation systems trade winds drive seasonal coastal upwelling and dust storm outbreaks from the neighbouring sahara desert are the major source of terrigenous sediment to investigate the forcing mechanisms for dust input and wind strength in the north canary basin the temporal pattern of variability of sedimentological and geochemical proxy records has been analysed in two sediment cores between latitudes 30 30 n and 31 40 n spectral analysis of the dust proxy records indicates that insolation changes related to eccentricity and precession are the main periods of temporal variation in the record si al and grain size of the terrigenous fraction show an increase in glacial interglacial transitions while al concentration and fe al ratio are both in phase with minima in the precessional index hence the results obtained show that the wind strength was intensified at terminations at times of maxima of northern hemisphere seasonal insolation when the african monsoon was enhanced the north canary basin also received higher dust input this result suggests that the moisture brought by the monsoon may have increased the availability of dust in the source region

glacial to interglacial changes in carbonate and clay sedimentation in the atlantic ocean estimated from 230th measurements abstract the cause of the climatically controlled fluctuations in the carbonate content of deep sea sediments remains the subject of uncertainty and debate three variables are involved supply of biogenic carbonate loss by dissolution and dilution by non carbonate phases it is suggested that 230 th which is produced in the ocean at a constant rate provides a reliable reference for measuring variations in rate of sedimentation on a regional scale results of a preliminary analysis based on published data indicate that for depths at and above the lysocline the carbonate fluctuations observed in cores from the north atlantic ocean are due primarily to variations in the terrigenous clay input which was 2 5 times higher during glacials than during interglacials carbonate deposition appears to have been somewhat reduced during glacials but probably not by more than a factor of 2 from published 230 th 232 th profiles it appears that the south atlantic ocean also received increased inputs of terrigenous clay during glacial periods

recent spatial and temporal changes in the stress regime along the southern tunisian atlas front and the gulf of gabes new insights from fault kinematics analysis and seismic profiles tectonic deformations in the southern atlassic front of tunisia saft and the gulf of gabes result from the nubia eurasia convergence this study based on the inversion of geologically determined fault slip vectors presents evidences for spatial and temporal changes in the stress state fault kinematics analyses reveal a temporal change in states of stress during the late cenozoic a paleostress miocene pliocene state is characterized by a regional compressional tectonic regime with a mean n134 09 e trending horizontal maximum stress axis 1 a modern quaternary to present day state of stress also corresponds to compressional tectonic regime with a regionally mean n05 10 e trending horizontal 1 the saft corresponds to two distinct domains a far foreland atlassic front related to contractional deformation associated with southward propagate thrusting and eastward the gulf of gabes characterized by normal component nw to wnw trending faults at the crustal margin scale probably related with a transtensional tectonic regime we propose that the spatial and temporal changes in the stress during the miocene pliocene and quaternary may result from the geodynamic evolution of the tunisian atlas in relation to the rotation of corsica sardinia blocks and the separation of the sicilian continental lithosphere from the ionian oceanic lithosphere these temporal and spatial stress changes along the saft and the gulf of gabes are probably the engine behind the moderate seismicity leading at the same time to a reactivation of the inherited major structures created during the evolution of the southern tethyan margin

new constraints on the nubia sinai dead sea fault crustal motion abstract the subduction between nubia and eurasia and activities along the red sea gulf of suez and gulf of aqaba may control the surface deformation in the north eastern corner of the african continent using very few gps stations in the egyptian region previous studies indicate northward motion of northern nubia with respect to eurasia of about 5 mm yr mcclusky et al 2000 reilinger et al 2006 mahmoud et al 2005 in order to constrain better the movement rate of northern nubia and interaction between nubia eurasia and arabia plates we are using for the first time 16 permanent gps stations in combination with 47 non permanent stations covering egypt for the period 2006 2012 this paper extends the previous study saleh and becker 2013 by processing in addition to the egyptian stations 86 permanent stations belonging to three different tectonic plates this led to a considerably better coverage of the sinai dead sea region this work intends to be the first comprehensive analysis of the permanent stations in combination with the various campaign data in selected regions of special interest in egypt the gps sites show a relative motion between nubia and eurasia of about 6 5 1 mm yr which increased toward the hellenic trench 8 2 0 8 mm yr in sinai peninsula 14 2 1 4 mm yr in the north of arabian plate and 22 3 0 7 mm yr in eastern and central turkey the strain computation indicates high strain rates where the deformation is strongly localized along the dead sea fault and low to moderate strain rate in the gulf of suez and southern sinai

tectonic evolution of the northern african margin in tunisia from paleostress data and sedimentary record abstract a reconstruction of the tectonic evolution of the northern african margin in tunisia since the late permian combining paleostress tectonic stratigraphic and sedimentary approaches allows the characterization of several major periods corresponding to consistent stress patterns the extension lasting from the late permian to the middle triassic is contemporaneous of the rifting related to the break up of pangea during liassic times regional extensional tectonics originated the dislocation of the initial continental platform in northern tunisia the evolution of the liassic ne sw rifting led during dogger times to the north african passive continental margin whereas in southern tunisia a n s extension associated with e w trending subsiding basins lasted from the jurassic until the early cretaceous after an upper aptian early albian transpressional event ne sw to ene wsw trending extensions prevailed during late cretaceous in relationship with the general tectonic evolution of the northeastern african plate the inversions started in the late maastrichtian paleocene in northern tunisia probably as a consequence of the africa eurasia convergence two major nw se trending compressions occurred in the late eocene and in the middle late miocene alternating with extensional periods in the eocene oligocene early middle miocene and pliocene the latter compressional event led to the complete inversion of the basins of the northwestern african plate originating the maghrebide chain such a study supported by a high density of paleostress data and including complementary structural and stratigraphic approaches provides a reliable way of determining the regional tectonic evolution

the influence of organic matter diagenesis on caco3 dissolution at the deep sea floor abstract in situ benthic flux chamber measurements were performed at seafloor locations in the atlantic and pacific oceans where the bottomwaters were supersaturated approximately saturated and undersaturated with respect to calcite there was no evidence of significant dissolution at or above the saturation horizon below the saturation horizon however significant benthic fluxes of titration alkalinity and calcium out of the sediments were observed indicating appreciable dissolution where observed the rate of dissolution is consistent with a rate expression of reaction order 4 5 and a rate constant in the range of 0 05 to 0 5 per day a numerical simulation was constructed to represent organic matter and caco3 diagenesis at the seafloor at the supersaturated and near saturation sites the model over predicts the influence of metabolically produced co2 on the extent of caco3 dissolution it is possible that these results can be reconciled by a better understanding and parameterization of organic matter mineralization and porewater transport processes in surface sediments the primary factors to be considered include 1 the oxidation state of the carbon being oxidized 2 the vertical distribution of oxidation rates including the role of doc in sediment remineralization 3 the influence of nondiffusive transport of near surface porewaters and 4 the influence of episodic depositional events on organic and inorganic carbon cycling

geodetic measurements of crustal deformation in the western mediterranean and europe geodetic measurements of crustal deformation over large areas deforming at slow rates 5 mm yr over more than 1000 km such as the western mediterranean and western europe are still a challenge because 1 these rates are close to the current resolution of the geodetic techniques 2 inaccuracies in the reference frame implementation may be on the same order as the tectonic velocities we present a new velocity field for western europe and the western mediterranean derived from a rigorous combination of 1 a selection of sites from the itrf2000 solution 2 a subset of sites from the european permanent gps network solution 3 a solution of the french national geodetic permanent gps network rgp and 4 a solution of a permanent gps network in the western alps regal the resulting velocity field describes horizontal crustal motion at 64 sites in western europe with an accuracy on the order of 1 mm yr or better its analysis shows that central europe behaves rigidly at a 0 4 mm yr level and can therefore be used to define a stable europe reference frame in that reference frame we find that most of europe including areas west of the rhine graben the iberian peninsula the ligurian basin and the corsica sardinian block behaves rigidly at a 0 5 mm yr level in a second step we map recently published geodetic results in the reference frame previously defined geodetic data confirm a counterclockwise rotation of the adriatic microplate with respect to stable europe that appears to control the strain pattern along its boundaries active deformation in the alps apennines and dinarides is probably driven by the independent motion of the adriatic plate rather than by the africa eurasia convergence the analysis of a global gps solution and recently published new estimates for the african plate kinematics indicate that the africa eurasia plate motion may be significantly different from the nuvel1a values in particular geodetic solutions show that the convergence rate between africa and stable europe may be 30 60 slower than the nuvelia prediction and rotated 10 30 counterclockwise in the mediterranean

200 000 yr diatom records from atlantic upwelling sites reveal maximum productivity during lgm and a shift in phytoplankton community structure at 185 000 yr abstract time series of diatom accumulation rates dar and assemblage composition for the last 200 000 yr from the atlantic major coastal upwelling loci of the eastern boundary currents and eastern equator are compared together with independent proxies of export production to upper ocean productivity and to nutrient concentration and utilization fluctuations in dar are concomitant at all sites and in good correspondence to the other independent productivity proxies indicating glacial periods as the most productive times of the past 200 000 yr in both hemispheres of the eastern atlantic maximum productivity about one order of magnitude higher than at present occurred at the last glacial maximum lgm despite the atlantic similarities in both coastal and equatorial upwelling types important regional and site specific variations emerge in the southern hemisphere site a contradiction of proxies diatoms and corg is noted at the base of stage 6 185 000 yr the good correlation found between the corg and the benthic foraminifera fluxes is interpreted as a reflection of a shift in the phytoplankton community structure related to either a change in the n p si ratio or similar nutrient conditions associated with increased water column stratification

active tectonics and gps data analysis of the maghrebian thrust belt and africa eurasia plate convergence in tunisia abstract the atlas mountains of tunisia belong to the seismically active zone of the africa nubia eurasia plate boundary in the central western mediterranean we study the eastern section of the maghrebian thrust belt using a subset 6 days from each of 5 years 2014 to 2018 of permanent survey mode gps data and active tectonics wnw to nnw trending velocities express crustal motion and geodetic strain fields from the sahara platform to the tell atlas consistent with african plate convergence to the south the velocities and trajectories indicate nearly wnw ese trending right lateral motion of the sahara fault related atlas fold belt with respect to the sahara platform farther north and northeast the significant decrease in velocities between the eastern platform sahel central atlas and tell atlas and the clockwise rotation mark the nnw trending shortening deformation associated with local ene wsw extension visible in the quaternary grabens the velocity field and strain distribution associated with the active e w to wnw ese trending right lateral faulting and ne sw fault related folds illustrate the transpression tectonics and support the identification of four tectonic domains north of the africa nubia platform in tunisia the transpression reduces northward when reaching the central and tell atlas these results change our perception of the africa eurasia plate boundary previously located along the western mediterranean coastline

the eastern boundary current system between the canary islands and the african coast to study the easternboundarycurrentsystem off northwest africa in detail several ctd adcp sections and long term mooring work were carried out in the channel between lanzarote and africa the observations are compared with a fine resolution model which was developed in the framework of the canigo project the water masses which are observed in this area are characterised and classified in density ranges the current field shows a high spatial and temporal variability with maximum velocities of about 35 cm s seasonal means as well as currents averaged across the channel are only a few cm s in the surface water a steady southward flow in the middle of the channel indicates the canarycurrent in this area during fall a strong northward current is observed close to the african shelf though the canarycurrent strengthens during summer and fall due to an increase of the trade winds the transport in the channel decreases or turns northward during that time due to the enhanced poleward current at the eastern side a northward undercurrent with a mean velocity of 2 3 cm s is observed at the african slope in 950 m depth the poleward transport of aaiw increases during fall and a strong influence of relatively fresh aaiw is observed during that time most of the observations fit well to the results of the canigo model but the occurrence of mw at the bottom of the channel and the corresponding southward flow cannot be resolved by the model

on the origin and consequences of crustal scale extension between africa and sicily since late miocene insights from the kaboudia area western pelagian sea abstract the eastern tunisian shelf is located between the gulf of hammamet and the gulf of gabes and belongs to the pelagian domain which underwent a continuous ne directed extension and crustal thinning since late miocene this geodynamic process induced the formation of nw striking normal faults and associated grabens both in the tunisian atlas and the pelagian domain including the sicily channel rifting zone scrz in this study we combine regional stratigraphy from seismic reflection profiles focal mechanisms space geodetic measurements gnss and thermal indicators from well data to propose a backward tectonic reconstitution of the pelagian domain the thinning of the continental crust is demonstrated by gravity inversion integrating published seismic refraction profiles by completing the interpretation of tectono stratigraphic records we highlight a northeastward propagation of extension prevailing within the pelagian shelf from messinian to plio quaternary times we suggest that extensional tectonics is explained by 1 eastward slab tearing between the african continental lithosphere and the tethyan oceanic slab allowing asthenospheric upwelling and 2 forces arising from relative motions between nubia and the hyblean malta block the decoupling of these domains since late miocene likely results from a combination of the nw directed plate convergence inherited rheological contrasts within the continental crust and weakening arising from mantle flow induced by the tethyan slab rollback and tearing

active oblique ramp faulting in the southern tunisian atlas abstract the gafsa fault is the longest and most active structure of the fold and thrust belt achieving southeastward propagation of the atlas belt of eastern north africa onto the saharan platform the gafsa fault is a 75 km long dextral oblique basement fault ramp that poses a sizable challenge in earthquake hazard assessment because the post paleozoic sedimentary cover is decoupled from its basement above the basement fault in this study we combine seismic lines interpretation tectonic geomorphology and paleoseismological investigations to assess the level of seismic hazard of this fault and evaluate its role in the geodynamic framework of the central mediterranean we show that despite a moderate instrumental and historical seismicity the fault has produced m 6 earthquakes with a return period of ca 500 5000 years during the late quaternary the latest large event having produced a surface rupture on the fault occurred around 8000 yr bp suggesting an m 6 earthquake is overdue on the fault the fault has a minimum reverse component of slip rate of 0 21 0 34 mm yr over the past 50 ka the occurrence of m 7 paleoearthquakes on the fault may be suspected but not established such very strong earthquakes would require transient coseismic linkage of the buried basement fault with the overlying listric fault ramping off the decollement layer the level of seismic hazard may be underestimated on the gafsa fault indeed given the geometry of the basement cover fault system a number of earthquakes generated in the basement would have led to coseismic surface folding instead of to surface rupture the gafsa fault is a major structure accommodating eastward extrusion spreading of the atlas belt onto the saharan and pelagian plateforms above the retreating ionian lithospheric slab

testing models of past ocean chemistry using foraminifera 15n 14n previous models have attempted to explain glacial to interglacial changes in atmospheric pco2 by invoking changes in the ocean s nutrient concentration or regional changes in nutrient utilization nitrogen is limiting to primary production and has a residence time in the ocean compatible with glacial to interglacial variations but up to now there has been no geological indicator for glacial to interglacial changes in the ocean s nitrogen cycle we propose that 15n 14n ratios for the organic matrix of preserved foraminifera yield an interpretable 15n record we have developed models to study the relationship between plausible changes in the ocean s nitrogen cycle and resulting changes in the 15n 14n ratio of dissolved no3 our model results demonstrate that 15n 14n ratios exhibit excursions during periods in which the oceans are accumulating or losing nitrogen regardless of the means by which these changes occur foraminifera 15n 14n results for a pacific and an atlantic core provide evidence against wide spread glacial anoxia a consequence of many models of ocean chemistry we suggest that increasing shelf sediment denitrification upon deglaciation reduced nitrogen concentrations in the modern ocean ambiguities between the two foraminifera 15n 14n records indicate that local effects associated with changes in hydrography or ecology need to be studied further

tectonosedimentary evidence in the tunisian atlas bou arada trough insights for the geodynamic evolution and africa eurasia plate convergence the bou arada trough is an east west oriented structure located 80 km sw of tunis characterizing the central tunisian atlas this trough is filled by a thick quaternary sand and clay series and is bordered by complex systems of folds generally trending ne sw contacts between the bou arada trough and the neighbouring folds are accommodated by ne sw and nw se oriented faults in contrast to the other troughs of the tunisian atlas which are related to the pliocene quaternary orogenic period the geodynamic evolution of the bou arada trough began in the maastrichtian and has continued until the present day structural tectonosedimentary and seismic data analyses are undertaken in the study area to better understand the evolutionary scenario of this trough the results obtained show that the bou arada trough is fragmented into three nw se oriented sub basins and records a continuous history of downthrow indeed during extensional to transtensional regimes this trough has evolved in response to the two networks of perpendicular fractures whereas during compressive to transpressive periods the collapse of the bou arada trough has been induced by a pull apart mechanism using the same network of faults but with a strike slip movement the bou arada trough thus preserves a record of the convergence between the european and african plates since the maastrichtian

evidence for local shifting of the main fault and changes in the structural setting kinarot basin dead sea transform two new high resolution seismic reflection profiles from the kinarot valley dead sea rift analyzed with older conventional oil exploration profiles throw light on the quaternary evolution of the african arabian transform type plate boundary in the area the present en echelon main faults of the dead sea transform are observed in the seismic data as wide zones of deformation rather than as distinct fault planes a similar zone of deformation is observed in the center of the kinarot basin and may be associated with an extinct trace of the main fault the zemah structure previously mapped and drilled is shown by the new data to be an inactive anticline compression within the basin is suggested as being the result of motion along the now inactive main fault observed in the center of the basin compression and shortening started some 2 m y ago and ended late in the quaternary as a result of changes in the geometry of the transform at present the kinarot basin is subsiding

surface sediment distribution along the chilean continental slope related to upwelling and productivity abstract the coastal upwelling system of the peru chile current belongs to the most productive regions in the world oceans in spite of this remarkable fact only very little is known about the sediment distribution in its southern part off the coast of chile to increase the knowledge about this region a multiparameter study of the surface sediment distribution along the chilean continental slope between 27 and 42 s has been carried out detailed analyses of sedimentary data toc and carbonate contents 13corg 15n of the species composition of planktic foraminifera and of the stable isotope composition of the two planktic foraminifera species neogloboquadrina pachyderma dex and globigerina bulloides reveal a close relation to environmental conditions in the region the pattern of a southward increase of surface water productivity known from satellite data is closely reflected in the organic carbon and 15n data information about the water mass distribution especially about varying influences of upwelling waters and warmer subtropical surface waters can be derived from the species composition of the planktic foraminifera while the stable isotope data provide additional clues about water mass characteristics high productivity along the chilean margin north of 40 s is sustained by coastal upwelling while further to the south advection of nutrients with the antarctic circumpolar current and a significant riverine input fuel the highest productivity found in the study area this data set will provide the base for future paleoclimatic and paleoceanographic reconstructions of the southeast pacific region

influence of lateral particle advection and organic matter degradation on sediment accumulation and stable nitrogen isotope ratios along a productivity gradient in the canary islands region abstract we compare total and biogenic particle fluxes and stable nitrogen isotope ratios 15n at three mooring sites along a productivity gradient in the canary islands region with surface sediment accumulation rates and sedimentary 15n higher particle fluxes and sediment accumulation rates and lower 15n were observed in the upwelling influenced eastern boundary region ebc compared to the oligotrophic sites north of gran canaria european station for time series in the ocean canary islands estoc and north of la palma lp the impact of organic matter degradation and lateral particle advection on sediment accumulation was quantified with respect to the multi year flux record at the estoc remineralisation of organic matter in the water column and at the sediment surface resulted in an organic carbon preservation of about 0 8 and total nitrogen preservation of about 0 4 of the estimated export production higher total and carbonate fluxes and accumulation rates in the lower traps and surface sediment compared to the upper traps indicated that at least 50 of the particulate matter at the estoc was derived from allochthonous sources low 15n values in the lower traps of the estoc and lp point to a source region influenced by coastal upwelling we conclude from this study that the reconstruction of export production or nutrient regimes from sedimentary records in regions with strong productivity gradients might be biased due to the mixture of particles originating from autochthonous and allochthonous sources this could result in an imprint of high productivity signatures on sedimentation processes in oligotrophic regions

surface ocean density gradients during the last glacial maximum we have compiled published planktonic foraminiferal oxygen isotope values from the tropical to subtropical atlantic and pacific for the late holocene and last glacial maximum lgm we interpret the spatial distribution of 18o values in terms of meridional density gradients in the lgm surface ocean and discuss implications on tropical ocean thermocline structure in both oceans glacial 18o values display a pattern of interhemispheric asymmetry evidenced by increasingly higher glacial 18o values toward northern latitudes the 18o derived density estimates suggest that the northern subtropical surface ocean density was higher during the lgm than today which has significant implications on lgm thermocline ventilation in the atlantic steeper density gradients in the northern subtropics during the lgm are consistent with a more compressed subtropical gyre and thermocline water formation farther south than today in the pacific the steeper density gradients suggest a significant reduction in freshwater fluxes to the northern tropical and subtropical regions which raises the possibility of a more significant component of northern hemisphere source waters to the tropical pacific thermocline these predictions could be tested with numerical ocean models that assess the structure of the tropical thermocline in the glacial ocean

regional and global benthic δ18o stacks for the last glacial cycle although detailed age models exist for some marine sediment records of the last glacial cycle 0 150 ka age models for many cores rely on the stratigraphic correlation of benthic 18o which measures ice volume and deep ocean temperature change the large amount of data available for the last glacial cycle offers the opportunity to improve upon previous benthic 18o compilations such as the lr04 global stack not only are the age constraints for the lr04 stack now outdated but a single global alignment target neglects regional differences of several thousand years in the timing of benthic 18o change during glacial terminations here we present regional stacks that characterize mean benthic 18o change for 8 ocean regions and a volume weighted global stack of data from 263 cores age models for these stacks are based on radiocarbon data from 0 to 40 ka correlation to a layer counted greenland ice core from 40 to 56 ka and correlation to radiometrically dated speleothems from 56 to 150 ka the regional 18o stacks offer better stratigraphic alignment targets than the lr04 global stack and furthermore suggest that the lr04 stack is biased 1 2 kyr too young throughout the pleistocene finally we compare global and regional benthic 18o responses with sea level estimates for the last glacial cycle

upwelling intensity and filament activity off morocco during the last 250 000 years abstract the high productive upwelling area off morocco is part of one of the four major trade wind driven continental margin upwelling zones in the world oceans while coastal upwelling occurs mostly on the shelf biogenic particles derived from upwelling are deposited mostly at the upper continental slope nutrient rich coastal water is transported within the cape ghir filament region at 30 n up to several hundreds of kilometers offshore both upwelling intensity and filament activity are dependent on the strength of the summer trades this study is aimed to reconstruct changes in trade wind intensity over the last 250 000 years by the analysis of the productivity signal contained in the sedimentary biogenic particles of the continental slope and beneath the cape ghir filament detailed geochemical and geophysical analyses toc carbonate c n 13corg 15n 13c of benthic foraminifera 18o of benthic and planktic foraminifera magnetic susceptibility have been carried out at two sites on the upper continental slope and one site located further offshore influenced by the cape ghir filament a second offshore site south of the filament was analyzed toc magnetic susceptibility to distinguish the productivity signal related to the filament signal from the general offshore variability higher productivity during glacial times was observed at all four sites however the variability of productivity during glacial times was remarkably different at the filament influenced site compared to the upwelling influenced continental slope sites in addition to climate related changes in upwelling intensity zonal shifts of the upwelling area due to sea level changes have impacted the sedimentary productivity record especially at the continental slope sites by comparison with other proxies related to the strength and direction of the prevailing winds si al ratio as grain size indicator pollen the productivity record at the filament influenced site reflects mainly changes in trade wind intensity our reconstruction reveals that especially during glacial times trade wind intensity was increased and showed a strong variability with frequencies related to precession

paleohydrology and paleoclimatology off northwest africa during the last glacial interglacial transition and the holocene palynological evidences abstract pollen and dinoflagellate cyst analyses of deep sea core located off morocco provide a continuous record of paleoclimatic and paleohydrological change off northwestern africa since the last glacial episode the stratigraphy is given by isotopic analysis 18 o of planktonic foraminifera which shows a two step deglaciation xeric conditions on the adjacent land marked by the increase of steppe taxa artemisia chenopodiaceae amaranthaceae ephedra and the development of the montane taxon cedrus atlantica are observed before termination ia and during the younger dryas these intervals are also marked by a high abundance of pinus pollen grains which indicates a strengthening of the northeastern ne trade winds variations of the surface water temperatures are shown by the fluctuations of dinoflagellate cyst assemblages which reflect a cooling of the surface waters during termination ia and the younger dryas episode intensification of the upwelling system off morocco resulting from enhanced trade winds occurred during these two key periods quercus forests which are an important part of the present day vegetation of the maghreb region developed around 8500 yr b p dinoflagellate cyst assemblages suggest that present day oceanic conditions were established during this period

new gps constraints on the africa eurasia plate boundary zone in southern italy 1 southern italy is a key area for understanding the tectonic processes in the africa eurasia collision zone we analyze new gps measurements carried out between 1994 and 2001 the results are presented in terms of time series trajectories and velocities of crustal motion as well as a geodetic strain rate field while central italy corsica sardinia and the tyrrhenian sea move like the eurasian plate the overall motion of the sicily rift zone region matches african plate motion unexpected are the north northwest directed motions of northeastern sicily and the eolian islands most striking on the deformation field are a north south oriented compression along the northern sicilian coast compression between apulia and northwestern greece as well as extension in the sicily rift zone and the interior of sicily

analogue modelling of late miocene early quaternary continental crustal extension in the tunisia sicily channel area abstract we adopt analogue modelling to investigate continental crustal stretching by simulating a late miocene early quaternary extensional event occurred in tunisia and in the sicily channel the analogue model of the continental crust is composed of a lower ductile crust and an upper brittle crust including a low viscosity layer to simulate the presence of evaporites in our models the extension is driven by tectonic stresses and not solely by gravity all models are run under the same boundary conditions with a moveable lateral edge different physical hypotheses are tested to interpret the origin and geometry of this rifting event that affected the sw sector of the mediterranean basin the modelling of the continental crustal stretching produces small tectonic troughs with regular spacing that simulates the pattern observed in the atlasic rift system tunisia as well as a large rift zone involving bulk crust thinning simulating the features of the sicily channel rift zone in accordance with geological and geophysical data extension in the atlasic rift zone is controlled at depth by the triassic evaporite layer and by inherited diapiric structures that create rheological soft points in the upper crust the best accordance between models and nature are thus obtained when combining crustal scale stretching decoupling level within the upper crust and pre structuration inheritance of the evaporitic layer we propose that the ne trending extensional event occurring since the pliocene to the early quaternary in the tunisian pelagian sea area was driven by a transient eastward migration of the tunisia pelagian ionian area acting as a micro plate with an undefined southern boundary due to a far field pull of the western hellenic dinaride subduction

organic matter preservation on continental slopes importance of mineralogy and surface area abstract theoretical considerations calculations and data reported by keil et al 1994a were used to assess the recent hypotheses that mineral surface roughness controls the specific surface area of continental margin sediments and that the matrix linked organic carbon content of continental margin sediments occurs as a monolayer or monolayer equivalent coating of organic compounds on the surfaces of detrital minerals and other detrital nonorganic grains mayer 1994 results of our analysis indicate that it is not the surface roughness of the terrigenous detrital framework grains that controls the specific surface area of most continental margin sediments even in the sand and silt fractions but rather the presence of nonspherical high surface area to volume particles primarily clays but also oxy hydroxides and ultra structured nonorganic bioclasts such as diatom frustules analysis of the mineralogy organic carbon content surface area and in situ microfabric of continental margin sediments off california in the mendocino and san luis obispo areas and off the state of washington indicate a strong correlation between the amount of matrix linked organic matter present and the suite of clay minerals data indicate that organic carbon appears to be preferentially sequestered in smectite rich sediments compared to those whose clay fractions are dominated by chlorite we suggest that this association is a function of differences in the site density and chemistry of the clays and differences in their flocculation behavior our data also indicate that organic carbon preservation on the three california transects all of which have a suboxic oxygen minimum zone that impinges on the sea floor is not significantly influenced by differences in bottom water oxygen concentration and carbon stable isotope data suggest no preferential preservation of continental organic matter over that of marine origin

upwelling intensity and ocean productivity changes off cape blanc northwest africa during the last 70 000 years geochemical and micropalaeontological evidence abstract the accumulation of biogeochemical organic carbon calcium carbonates molybdenum and iodine micropalaeontological benthic foraminifera and terrigenous markers grain size si al zr al k al over the last 70 000 years in one core sedorqua 11k on the northwest african margin off cap blanc has been used to reconstruct past variations of local upwelling intensity and oceanic productivity the study demonstrates that productivity in this area increased during stage 3 particularly between 40 000 and 50 000 yr b p and during the last deglaciation between 6000 and 15 000 yr b p during most of isotopic stage 2 and particularly during the last glacial maximum productivity was much lower these variations can be attributed to changes in local wind stress and seasonality that are related to variability in monsoon pressure intensity because of the establishment of upwelling cells over the shelf due to high sea level the conditions of sedimentation during the last 5 6 thousend years on the upper slope site 11k are largely dominated by advection from the shelf leading to strong sorting prior to deposition advection seems to have been minor during the other periods of enhanced productivity a conceptual model is proposed to link the productivity variations to atmospheric circulation in particular to the wind stress direction and seasonality

organic content and preservational controls in surficial shelf and slope sediments from the arabian sea pakistan margin abstract in the arabian sea organic rich deposits occur on the continental slope at depths roughly coincident with the impingement of an intense water column oxygen minimum zone omz this relationship has often been taken as causal and such deposits are often proposed as modern analogues of organic rich facies from the palaeorecord however there are numerous other potential preservational controls on continental margins and their relative importance remains unclear and much debated we report the results of organic inorganic and stable c isotope analyses on surficial sediments from three transects of the pakistan margin ranging in depth from well above to well below the omz organic carbon c org and total nitrogen n total contents show expected mid slope maxima although these do not mirror bottom water dissolved o 2 profiles maximal values are observed near the lower boundary of the omz or even in homogenous sediments below it together lignin yields and 13 c org values indicate a general paucity of terrigenous organic matter om this information combined with c org n total relationships suggests that the om contents of all sediments are dictated by differing accumulation of a predominant marine fraction while there are no obvious redox related differences in c org n total or om hydrogen richness across the margin there are clear minima in 13 c org within the omz in apparent contradiction with maximal accumulation of marine om the latter phenomenon is ascribed either to local source effects such as variable algal isotopic signatures or to differences in om preservation state possibly linked to bottom water redox conditions this remains to be clarified but along with the rough correspondence between mid slope sedimentary c org maxima and bottom water o 2 minima may indicate that o 2 availability is an important factor in determining sedimentary om content on this margin however evidence from redox sensitive indicators i c org mn al for persistent accumulation of om rich deposits under oxidizing conditions in homogeneous sediments below the omz clearly indicates that o 2 availability is not the sole or over riding control on om distributions

mid depth oxygen drawdown during heinrich events evidence from benthic foraminiferal community structure trace fossil tiering and benthic δ13c at the portuguese margin abstract the distribution of trace fossils and benthic foraminiferal assemblages in two sediment cores from 2160 m water depth at the northern and 1100 m at the southern portuguese continental margin was used to reconstruct the bottom water oxygenation during the last 40 ka emphasis was given to the heinrich events during which enhanced meltwater flux associated with the iceberg surges reduced or even halted deep water formation in the north atlantic condensed trace fossil tiering structures and high proportions of low oxygen tolerant benthic foraminifera suggest a major drawdown of bottom water oxygenation during heinrich events using the benthic foraminiferal oxygenation index bfoi of kaiho 1991 1994 that links benthic foraminiferal communities to ambient bottom water oxygenation we extracted apparent oxygen concentrations from benthic assemblages bfoi values suggest low oxic conditions during heinrich events 1 and 4 with mean oxygen levels of 2 6 to 2 8 ml l 1 and high oxic conditions with 4 1 ml l 1 during heinrich event 2 at the shallower site high proportions of low oxygen tolerant foraminiferal species and bfoi minima are recorded a few centimetres below the maximum concentrations of ice rafted debris indicating that the original microhabitat depth of dysoxic species is preserved beneath the heinrich layers even though bioturbation continued during the events trace fossil tiering calibrated with the redox boundary in low oxic environments and dysoxic ichnotaxa commonly associated with black shales indicate oxygen levels lower than those implied by the bfoi oxygenation estimates derived from trace fossil tiering denote low oxic conditions during h1 13 3 ka with oxygen concentrations slightly above 1 ml l 1 and dysoxic conditions during h2 20 6 ka h3 27 ka and h4 33 5 ka with oxygen concentrations between 0 1 and 1 ml l 1 during the younger dryas bottom waters likely were low oxic negative excursions of benthic carbon isotope values provide independent control on the oxygen drawdown during heinrich events considering a bottom water oxygenation of 6 1 to 6 5 ml l 1 during the last glacial the benthic 13 c minima reveal an oxygen depletion to values between 3 4 and 5 0 ml l 1 during h1 through h4 at the shallower core site differences between estimates from benthic 13 c bfoi and trace fossil tiering suggest that benthic foraminiferal communities are rather robust to oxygen depletion if the level does not fall below 3 ml l 1 whereas burrowing organisms react sensitively to depth variations of the redox boundary in near surface sediments due to even small changes of bottom water oxygenation

active fault segmentation in northern tunisia abstract active shortening structures in northern tunisia have developed by tectonic inversion since the pliocene after late miocene extensional collapse of the whole region restored plio quaternary deformation observed on reflection seismic lines indicates deformation rates around 0 6 0 8 mm yr in the studied segments and larger amounts of shortening to the west of northern tunisia 16 than to the east 7 which suggests tectonic inversion started earlier to the west and later propagated eastwards reaching northeastern tunisia in the late pliocene this shortening is registered on striated pebbles in quaternary alluvial terraces and fault slip data giving two populations of strain ellipsoids with n s and wnw ese maximum shortening morphometric analysis in combination with field fault segmentation mapping show that topographic uplift and drainage rejuvenation occurs in relation to 20 30 km long ene wsw reverse fault segments and related antiforms that are offset and linked by e w to wnw ese dextral and ne sw oriented sinistral faults the largest fully linked fault system is the alia thibar fault this 130 km long fault zone shows an helicoidal geometry with five different fault segments including reverse dextral sinistral and oblique faults due to the young age of tectonic inversion after late miocene extensional collapse of the region the present relief of northern tunisia is characteristic of a young thrust and fold belt with dominating axial valleys along synforms and an incipient transverse drainage development propagating from west to east

an integrated view of inorganic and organic biogeochemical indicators of palaeoproductivity changes in a coastal upwelling area in order to evaluate the role of the continental margin areas in the changes of atmospheric co2 during past climatic cycles it is crucial to reconstruct reliably export palaeoproductivity changes in such areas this paper examines and discusses the specific relationships between various productivity dependent geochemical signals recorded in a single sediment core from the northwestern africa continental slope including both major and trace parameters of inorganic and organic origin this paper clearly shows that the export productivity flux as well as its composition e g the relative contribution of calcareous siliceous and mineral free producers have changed these changes have subsequently modified benthic conditions which can have had in turn a retroaction on major biogenic element contents this effect seems however to be only minor compared to that one directly induced by changes in biogenic fluxes these results indicate that direct palaeoproductivity transfer functions which are based on present day statistical calibrations of one single parameter and which are valid to some extent for sediments from abyssal open ocean cannot be properly applied in marginal areas which are much more complex and in particular highly affected by sea level changes in such areas quantitative palaeoproductivity reconstructions should be only considered at a regional scale including off shoreward on shoreward and latitudinal migration or extension of the productive areas as well as the palaeoproductivity intensity and composition

deformation styles related to intraplate strike slip fault systems of the saharan tunisian southern atlas north africa new kinematic models the complex geometry and tectonic evolution of the saharan tunisian southern atlas strike slip fault systems north africa have not been investigated comprehensively to date this paper proposes new conceptual models to better understand the structural styles along these intraplate fault zones we use a multidisciplinary approach including field observations geological mapping stress analysis and seismic data to investigate the development and interaction of major strike slip fault segments the regional fault system is dominated by the e w trending biskra alima orbata bouhedma and chotts basement faults that constitute the principal displacement zones pdzs our analyses and interpretations reveal that each pdz has a typical dextral strike slip architecture comprising multi scale fault segments that are linked through extensional and contractional stepovers bends during mesozoic times under ne sw shmin the transtensional fault segments of biskra and alima formed the boundaries of the khanguet sidi neji gafsa ksg basin which developed as a z shaped dextral releasing stepover in cenozoic the ksg basin was inverted in response to the africa eurasia convergence when there was a regional nw se orientation for maximum horizontal stress this inversion occurred mainly along basin sidewalls by reactivation of the pre existing normal oblique faults as right lateral transpressional shears further east the e w dextral strike slip faults of orbata and bouhedma are connected via a ne sw restraining stepover finally all e w dextral strike slip fault segments are associated with ene right stepping en echelon folds and riedel shear patterns of different scales in response to basement wrenching currently most fault zones are still active with deep strike slip earthquakes

modern tectonic stress field in the mediterranean region evidence for variation in stress directions at different scales summary a compilation of more than one thousand stress indicators which include in situ stress measurements focal mechanisms microtectonic and other geological data allowed us to reconstruct the modern stress field in the mediterranean region and the surrounding area average stress directions at different scales have been reconstructed by means of a linear interpolation method this method takes into account the distribution scale and quality of stress data the results of the interpolation at plate scale allow us to recognize slightly deformed regions such as the northwestern european platform where average maximum horizontal stress direction is oriented roughly nnw sse subparallel to absolute and relative plate velocity directions other regions such as the caucasus alps and pyrenees where recent tectonic deformation and seismicity are present display important variations of stress directions the reconstruction of the average stress directions at different scales within the french alps pointed out that the average stress field pattern may vary from one scale to another nevertheless variations of stress directions at a given scale are consistent with the kinematics of faults of the same scale

crustal motion along the eurasia nubia plate boundary in the calabrian arc and sicily and active extension in the messina straits from gps measurements 1 we investigate crustal deformation along the eurasia nubia plate boundary in calabria and sicily revealed by the gps velocity field obtained by the combination of continuous site velocities with previous results from episodic campaigns we recognize two distinct crustal domains characterized by different motions and styles of deformation convergence in sicily is taken up by crustal shortening along the former tyrrhenian back arc passive margin in agreement with seismological data and geological evidence of recent cessation of deformation along the plio pleistocene subduction front the analysis of the gps data and the consistency between earthquake slip vectors and convergence direction suggest that eu nu convergence in sicily does not require intermediate crustal blocks significant eurasia 3 mm yr to nne and nubia fixed 5 mm yr to ese residual velocities in calabria suggest instead the presence of an intermediate crustal block which can be interpreted as a forearc sliver or as an independent ionian block according to the first hypothesis subduction is still active in the ionian wedge although we find no evidence for active back arc spreading in the tyrrhenian sea the n115 e oriented sicily calabria gps relative motion is consistent with the extension observed during the 1908 mw 7 1 messina earthquake we suggest that up to 3 mm yr 80 of this estimated relative motion between sicily and the calabrian arc may be taken up in the messina straits

new gps constraints on active deformation along the africa iberia plate boundary abstract we use velocities from 65 continuous stations and 31 survey mode gps sites as well as kinematic modeling to investigate present day deformation along the africa iberia plate boundary zone in the western mediterranean region the gps velocity field shows southwestward motion of the central part of the rif mountains in northern morocco with respect to africa varying between 3 5 and 4 0 mm yr consistent with prior published results stations in the southwestern part of the betic mountains of southern spain move west southwest with respect to eurasia 2 3 mm yr the western component of betics motion is consistent with partial transfer of nubia eurasia plate motion into the southern betics the southward component of betics motion with respect to iberia is kinematically consistent with south to southwest motion of the rif mountains with respect to africa we use block modeling constrained by mapped surface faults and seismicity to estimate the geometry and rates of strain accumulation on plate boundary structures our preferred plate boundary geometry includes one block between iberia and africa including the sw betics alboran sea and central rif this geometry provides a good fit to the observed motions suggesting a wide transpressive boundary in the westernmost mediterranean with deformation mainly accommodated by the gloria azores fault system to the west and the rif tell lineament to the east block boundaries encompass aspects of earlier interpretations suggesting three main deformation styles i extension along the ne sw trending trans alboran shear zone ii dextral strike slip in the betics corresponding to a well defined e w seismic lineament and iii right lateral strike slip motion extending west to the azores and right lateral motion with compression extending east along the algerian tell we interpret differential motion in the rif alboran betic system to be driven both by surface processes related the africa eurasia oblique convergence and sub crustal dynamic processes associated with the long history of subduction of the neotethys ocean lithosphere the dextral slip identified in the betic mountains in southern spain may be related to the offshore fault that produced the great 1755 lisbon earthquake and as such may represent a significant seismic hazard for the west mediterranean region

strain rate tensor in iran from a new gps velocity field the aim of this paper is to determine the strain rate tensor srt for the iranian region in this study 1 we apply a method of computation of the srt never used for the iranian area and 2 we use a new gps velocity field obtained from several previously published velocity fields first the method is described and tested on a synthetic case which mimics the real iranian case the synthetic tests confirm that the method allows us to both retrieve high gradients of the strain rate field and reduce the effect of an erroneous velocity vector second the method is applied to a real data set covering the arabia eurasia collision zone in iran we particularly focus on the zagros makran transition zone the central iran region and the northernmost part of the arabia eurasia collision zone nw iran caucasus east turkey whereas themain characteristics of the obtained srt are consistent with known tectonic features important new results are found in the central iran with the strike slip style along the anar and deshir faults and the zagros makran transition zone with a north south variation of the srt along the zendan minab palami fault system we link these results to recent active tectonic studies

productivity response in the north canary basin to climate changes during the last 250 000 yr a multi proxy approach we present results from the investigation of the primary productivity record over the last 250 kyr in the north canary basin 30 n off northwest africa two distinct productive systems interfere in this area the oligotrophic open ocean and the upwelling filament off cape ghir that occasionally carries offshore cool nutrient rich waters the following geochemical and micropaleontological paleoproductivity proxies have been used in our study calcium carbonate barium excess baexcess total organic carbon toc and diatoms time series analysis of these proxies indicates that paleoproductivity in the north canary basin underwent important changes following precession and eccentricity cycles while the precessional signal appears to be mainly related to trade wind strength superimposed peaks in baexcess toc and diatom records point to large productivity events at terminations i ii and iii lowering of the north atlantic sea surface temperatures by melt water discharges which in turn strengthened the azores high pressure center and increased trade wind velocities is postulated as the mechanism to explain the enhancement of the coastal upwelling and associated filaments at terminations additionally the canary current may play a role in transmitting cold melt waters and nutrients from higher latitudes to the north canary basin

changes in east atlantic deepwater circulation over the last 30 000 years eight time slice reconstructions using 95 epibenthic 13c records eight time slices were reconstructed to trace the distribution of east atlantic deepwater and intermediate water masses over the last 30 000 years our results show that there have been three distinct modes of deepwater circulation near the stage 3 2 boundary the origin of north atlantic deep water nadw was similar to today mode 1 however after late stage 3 the source region of the nadw end member shifted from the norwegian greenland sea to areas south of iceland mode 2 a reduced nadw flow persisted during the last glacial maximum with constant preformed 13c values the nutrient content of nadw increased markedly near the azores fracture zone from north to south probably because of the mixing of upwelled antarctic bottom water aabw from below which then advected with much higher flux rates into the northeast atlantic later the spread of glacial meltwater over the north atlantic led to a marked short term ventilation minimum below 1800 m about 13 500 14c years ago mode 3 the formation of nadw recommenced abruptly north of iceland 12 800 12 500 years ago and reached a volume approaching that of the holocene in the younger dryas 10 800 10 350 years b p another short term shutdown of deepwater formation followed between 10 200 and 9 600 years b p linked to a further major meltwater pulse into the atlantic each renewal of deepwater formation led to a marked release of fossil co2 from the ocean the likely cause of the contemporaneous 14c plateaus over the last 9000 years deepwater circulation varied little from today apart from a slight increase in aabw about 7000 14c years ago it is also shown that the oxygenated mediterranean outflow varied largely independent of the variations in deepwater circulation over the last 30 000 years

active faulting geometry and stress pattern near complex strike slip systems along the maghreb region constraints on active convergence in the western mediterranean the maghreb region from tunisia to gibraltar is a key area in the western mediterranean to study the active tectonics and stress pattern across the africa eurasia convergent plate boundary in the present study we compile comprehensive data set of well constrained crustal stress indicators from single focal mechanism solutions formal inversion of focal mechanism solutions and young geologic fault slip data based on our and published data analyses stress inversion of focal mechanisms reveals a first order transpression compatible stress field and a second order spatial variation of tectonic regime across the maghreb region with a relatively stable s hmax orientation from east to west therefore the present day active contraction of the western africa eurasia plate boundary is accommodated by 1 e w strike slip faulting with reverse component along the eastern tell and saharan tunisian atlas 2 a predominantly ne trending thrust faulting with strike slip component in the western tell part and 3 a conjugate strike slip faulting regime with normal component in the alboran rif domain this spatial variation of the present day stress field and faulting regime is relatively in agreement with the inferred stress information from neotectonic features according to existing and newly proposed structural models we highlight the role of main geometrically complex shear zones in the present day stress pattern of the maghreb region then different geometries of these major inherited strike slip faults and its related fractures v shaped conjugate fractures horsetail splays faults and riedel fractures impose their component on the second and third order stress regimes neotectonic and smoothed present day stress map mean s hmax orientation reveal that plate boundary forces acting on the africa eurasia collisional plates control the long wavelength of the stress field pattern in the maghreb the current tectonic deformations and the upper crustal stress field in the study area are governed by the interplay of the oblique plate convergence i e africa eurasia lithosphere mantle interaction and preexisting tectonic weakness zones

glacial interglacial variability of particle accumulation in the canary basin a time slice approach abstract particle supply and sediment accumulation in the canary basin are strongly modified by seasonal coastal upwelling and dust input from the sahara along an e w depth profile and fertility gradient north of the canary islands we demonstrate an increase in total mass accumulation rates from a low of 1 2 g cm 2 ka 1 in the outer oceanic domain to 6 12 g cm 2 ka 1 closer to the moroccan shelf in holocene sediments during the last glacial maximum lgm oxygen isotopic event 2 2 a steeper gradient was found with two to four times higher mass accumulation rates at the near shore sites total mass accumulation rates during the last interglacial climax lic isotopic event 5 5 and end of the penultimate glaciation epg isotopic event 6 2 resemble holocene values with lowered near shore maxima of 3 and 4 g cm 2 ka 1 respectively analyses of separate sediment components show that total organic carbon total carbonate lithogenic and diatom accumulation rates were generally enhanced during glacial times especially during the lgm in contrast glacial accumulation rates of biogenic carbonate particles coccoliths and planktic foraminifera shells remained constant or were lowered with respect to interglacial time periods at the site closest to the moroccan shelf despite a doubling of bulk carbonate accumulation this could indicate lowered supply from the productive euphotic zone or a latitudinal offshore shift of the main sedimentary depocentre however enhanced carbonate dissolution could by itself account for this decrease in biogenic carbonate accumulation increased glacial input of detrital carbonate derived from the exposed moroccan shelf appears to be responsible for the overall enhanced carbonate accumulation at the same sites east of lanzarote