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

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

calcareous dinoflagellate cyst distributions in surface sediments from upwelling areas off nw africa and their relationships with environmental parameters of the upper water column abstract only very few studies have focussed on the spatial distribution and ecology of calcareous dinoflagellate cysts dinocysts in upwelling areas here distributions of individual calcareous dinocyst species in surface sediment samples from the coastal upwelling zone off nw africa and their relationships with known environmental parameters of the sub surface waters have been analysed in order to enhance our knowledge on their modern distribution patterns and to determine the ecological significance and palaeoenvironmental reconstruction potential of each calcareous dinocyst species within this exemplary high productivity region in addition to calculating relative cyst abundances well constrained sedimentation rates have allowed the calculation of dinocyst accumulation rates cysts cm 2 ka 1 for most of the surface sample positions thus providing a much more accurate estimation of actual calcareous dinocyst production in the upper water column than could be warranted in similar studies so far distinct differences in the geographic distribution patterns of nine species were observed in general high accumulation rates of calcareous dinocysts were found around and south of 29 n and offshore the westernmost canary island la palma with slightly lower accumulation rates in the upwelling influenced areas off cape yubi and in the upwelling filament area off cape ghir multivariate ordination techniques were applied in order to compare the cyst accumulation rates of individual species with physical parameters temperature salinity density mixed layer depth and the trophic state nitrate phosphate and chlorophyll concentrations of the overlying sub surface waters all species were found to relate significantly to one or more of the environmental parameters partly confirming previous results on cyst ecology but also providing new information which will be useful for future palaeoenvironmental reconstructions within upwelling areas

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

the arid humid transition in the sahara and the sahel during the last deglaciation at the time of the last glacial maximum the sahara and sahel regions of north africa were extremely dry new records of rainfall show that during the subsequent deglaciation the transition from arid to humid conditions in these regions occurred synchronously in two main steps comparison with other records of palaeoclimate in europe and the north atlantic ocean shows that certain common factors controlled changes in ocean and atmosphere dynamics during the deglaciation

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

marine and terrestrial biomarker records for the last 35 000 years at odp site 658c off nw africa several high resolution proxy environmental records have been obtained for the last 35 kyr from odp hole 658c a well studied site ca 200 km oa cap blanc nw africa the collective assessment based on the marine proxies u k 0 37 sst contents of toc and chlorins upwelling radiolarian index and the percentage of florisphaera profunda surprisingly indicates that the last glacial maximum lgm was characterized by warmer sea surface temperature sst weaker upwelling and lower marine productivity compared with the preceding older glacial and subsequent deglaciation periods of the terrigenous proxies the mean grain size of the non carbonate fraction and the terrigenous alkane content indicate that wind strength and aridity were high the weaker upwelling at the 658 site during the lgm may have resulted from changes in the strength and direction of the wind systems and or shifts in the position and geometry of the upwelling cell 2000 elsevier science ltd all rights reserved

storminess control over african dust input to the moroccan atlantic margin nw africa at the time of maxima boreal summer insolation a record of the last 220 kyr abstract precessional forcing of dust flux from northwest africa to the atlantic during the last 220 kyr is recognised through changes in physical and chemical sediment properties sediment colour reflectance magnetic susceptibility x ray fluorescence element intensity in a core from the moroccan margin sediment colour reflectance magnetic susceptibility and ca and fe element intensity changes are thought to be driven by dust input from north africa spectral analysis of the sediment properties records displays a dominant periodicity in the 1 23 kyr 1 frequency band that is associated with the earth s orbital precession peaks in terrigenous supply match precessional minima this suggests a close link between maxima of boreal summer solar radiation monsoon activity and dust generation enhanced precession driven solar radiation would have caused increased seasonal temperature contrasts which amplified atmospheric turbulence and stimulated storminess such a scenario is similar to today s summer conditions when frequent storms cause distinct dust plumes to form in the area and transport fine terrigenous material to the adjacent north atlantic ocean

radiometric 81kr dating identifies 120 000 year old ice at taylor glacier antarctica we present successful 81kr kr radiometric dating of ancient polar ice krypton was extracted from the air bubbles in four 350 kg polar ice samples from taylor glacier in the mcmurdo dry valleys antarctica and dated using atom trap trace analysis atta the 81kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean absolute age offset of 6 2 5 ka our experimental methods and sampling strategy are validated by i 85kr and 39ar analyses that show the samples to be free of modern air contamination and ii air content measurements that show the ice did not experience gas loss we estimate the error in the 81kr ages due to past geomagnetic variability to be below 3 ka we show that ice from the previous interglacial period marine isotope stage 5e 130 115 ka before present can be found in abundance near the surface of taylor glacier our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available greatly enhancing their scientific value as archives of old ice and meteorites at present atta 81kr analysis requires a 40 80 kg ice sample as sample requirements continue to decrease 81kr dating of ice cores is a future possibility

glacial and interglacial wind regimes over the eastern subtropical atlantic and north west africa analysis of aeolo marine dust deposits in the subtropical eastern atlantic enables the strength of the major wind patterns during the late quaternary to be evaluated and gives an insight into the climate of north africa

variability of the antarctic intermediate waters in the northern canary box abstract several chemical parameters were measured during four seasonal cruises in 1997 and 1998 within the canary islands acores gibraltar observations project along the transects within the so called northern canary box ncb this area is enclosed between the african coast latitudes 29 n and 32 n and longitude 18 w to the north of the canary islands spain the nutrient and oxygen concentration data are used in order to establish the atlantic antarctic intermediate water aaiw distribution in the area by means of an anomaly method it is established that this water mass is widely found in this zone particularly new to the african coast a volumetric budget indicates that the aaiw volume flowing into the ncb is of the same order as the mediterranean water mw inflow the results indicate that only 40 of the aaiw mass reaching the box flows northwards through the 32 n section whereas 20 returns southwards through the 29 n section

reliability of relative palaeointensities of a sediment core with climatically triggered strong magnetisation changes abstract a late pleistocene deep sea core was taken in the central atlantic near the coast of mauritania large variations of magnetic properties such as natural and anhysteretic remanent magnetisation nrm arm and low field susceptibility k as well as their ratios nrm k and arm k coincide with oxygen isotope ratio changes warm periods mainly correspond to high magnetisations and cold periods to low ones these variations are mainly due to concentration changes of fine grained magnetite and less to changes of chemistry and grain size of ferromagnetic minerals therefore arm is preferred as a normalisation parameter for nrm the nrm arm ratio reflects to a much lesser degree climatic and mineralogical changes previous investigations established quality criteria and limits of the variations of ferromagnetic minerals and related magnetic properties for reliable relative palaeointensity measurements these limits are largely exceeded in the present study however the ages of most prominent nrm arm ratio lows and highs are in agreement with published relative palaeointensity data therefore it is concluded that the general trend of the earth s magnetic field intensity changes can be preserved even in a sediment core with strong ferromagnetic mineral variations

global variations of surface ocean productivity in low and mid latitudes influence on co2 reservoirs of the deep ocean and atmosphere during the last 21 000 years based on detailed reconstructions of global distribution patterns both paleoproductivity and the benthic 13c record of co2 which is dissolved in the deep ocean strongly differed between the last glacial maximum and the holocene with the onset of termination i about 15 000 years ago the new export production of low and mid latitude upwelling cells started to decline by more than 2 4 gt carbon year this reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric co2 as recorded in ice cores and with a slight delay of more than 1000 years to a large scale gradual co2 depletion of the deep ocean by about 650 gt c this estimate is based on an average increase in benthic 13c by 0 4 0 5 the decrease in new production also matches a clear 13c depletion of organic matter possibly recording an end of extreme nutrient utilization in upwelling cells as shown by sarnthein et al 1987 the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades which in turn was linked via a shrinking extent of sea ice to a massive increase in high latitude insolation i e to orbital forcing as primary cause

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

turbidite emplacement on the southern balearic abyssal plain western mediterranean sea during marine isotope stages 1 3 an application of itrax xrf scanning of sediment cores to lithostratigraphic analysis the upper part 0 20 m of a long piston core from the se balearic abyssal plain spanning the past 50 ka has been studied using the itrax micro xrf core scanner to obtain downcore elemental profiles the ca fe ratio was found to be an effective parameter to distinguish between turbidites and pelagites because turbidites generally have higher fe contents and lower ca contents compared with pelagic intervals beds that were obscure when visually logged could be identified as turbidites or pelagites on their geochemical characteristics allowing more complete subdivision of the sequence into genetic units the itrax xrf data also provide useful information on textural grading bioturbative mixing identification of geochemically distinctive marker beds indications of differences in provenance and confirm or query the presence of early arrivals during turbidite emplacement a chronostratigraphic framework for the core based on accelerator mass spectrometry ams radiocarbon dating and correlation with oxygen isotope stages of pelagic intervals in other cores using calcium carbonate stratigraphy was also established this shows that turbidite emplacement on this part of the balearic abyssal plain has been modulated strongly by climate and sea level change with turbidite emplacement most frequent during the early holocene when the rate of post glacial sea level rise was greatest deposition of the coarsest i e sand and silt based turbidites at the core site was restricted to the full and late glacial 11 25 ka turbidite emplacement during oxygen isotope stage 3 was rare most of the turbidites at the site are distal but some coarse grained based turbidites are characterized by higher sr ca ratios possibly indicating a higher aragonite content higher ca and lower fe contents compared to other turbidites and are interpreted as having a more proximal shelf source such turbidites are generally rare however and restricted to full glacial and younger dryas time there is little evidence for large scale seismogenic turbidites expected to be seen as randomly timed emplacement seemingly independent of eustatic control at the core site despite proximity to the seismically active algerian margin 100 km to the south this suggests that seismogenic turbidites must largely bypass this part of the plain although the itrax core scanner provides a rapid and non destructive means of characterizing downcore geochemical distributions in great detail interpretation of the data requires caution and assessment from an informed standpoint analytical artefacts such as those caused by water or organic content degree of compaction grain size and mineral effects unevenness of the cut core surface and poor discrimination of closely spaced element xrf peaks need identification and elimination

thermohaline instability in the north atlantic during meltwater events stable isotope and ice rafted detritus records from core so75 26kl portuguese margin a benthic isotope record has been measured for core so75 26kl from the upper portuguese margin 1099 m water depth to monitor the response of thermohaline overturn in the north atlantic during heinrich events evaluating benthic 18o in ts diagrams in conjunction with equilibrium c fractionation implies that advection of mediterranean outflow water mow to the upper portuguese margin was significantly reduced during the last glacial 15 compared to 30 today the benthic isotope record along core so75 26kl therefore primarily monitors variability of glacial north atlantic conveyor circulation the 14c accelerator mass spectrometry ages of 13 54 07 and 20 46 12 ka for two ice rafted detritus ird layers in the upper core section and an interpolated age of 36 1 ka for a third ird layer deeper in the core are in the range of published 14c ages for heinrich events h1 h2 and h4 marked depletion of benthic 13c by 0 7 1 1 during the heinrich events suggests reduced thermohaline overturn in the north atlantic during these events close similarity between meltwater patterns inferred from planktonic 18o at site 609 and ventilation patterns inferred from benthic 13c in core so75 26kl implies coupling between thermohaline overturn and surface forcing as is also suggested by ocean circulation models benthic 13c starts to decrease 1 5 2 5 kyr before heinrich events hl and h4 fully increased values are reached 1 5 3 kyr after the events indicating a successive slowdown of thermohaline circulation well before the events and resumption of the conveyor s full strength well after the events benthic 13c changes in the course of the heinrich events show subtle maxima and minima suggesting oscillatory behavior of thermohaline circulation a distinct feature of thermohaline instability in numerical models inferrred gradual spin up of thermohaline circulation after hl and h4 is in contrast to abrupt wanning in the north atlantic region that is indicated by sudden increases in greenland ice core 18o and in marine faunal records from the northern north atlantic from this we infer that thermohaline circulation can explain only in part the rapid climatic oscillations seen in glacial sections of the greenland ice core record

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

reconstruction of paleoceanography off nw africa during the last 40 000 years influence of local and regional factors on sediment accumulation abstract a set of 43 sediment cores from around the canary islands is used to characterise this region which intersects meridional climatic regimes and zonal productivity gradients in a high spatial resolution using rapid and nondestructive core logging techniques we carried out fe intensity and magnetic susceptibility ms measurements and created a stack on the basis of five stratigraphic reference cores for which a stratigraphic age model was available from 18 o and 14 c analyses on planktonic foraminifera by correlation of the stack with the fe and ms records of the other cores we were able to develop age depth models at all investigated sites of the region we present the bulk sediment accumulation rates ar of the canary islands region as an indicator of shifts in the upwelling influenced areas for the holocene 0 12 ky the deglaciation 12 18 ky and the last glacial 18 40 ky general observations are an enhanced productivity during glacial times with highest values during the deglaciation the main differences between the analysed time intervals we interpret as result of the sea level effects changes in the extent of high productivity areas and current intensity

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

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

influence of the water content on x ray fluorescence core scanning measurements in soft marine sediments the x ray fluorescence xrf core scanner provides bulk sediment chemistry data measured nondestructively at the split core sediment surface although this method is widely accepted there is little known about the effects of physical properties such as density and water content on xrf core scanner data comparison of xrf scanner measurements from the sediment surface and dry powder samples of sediment core geob7920 indicates strongly reduced element intensities for the lighter elements al and si we relate the lower element intensities of the measurements taken at the sediment surface to the amount of water in the sample volume analyzed by the xrf core scanner the heavier elements k ca ti and fe remain relatively unaffected by the variation of any physical property within sediment core geob7920 additionally we successfully use the elemental intensity of cl as a proxy for the seawater content in the sample volume analyzed by the xrf core scanner this enables the establishment of a correction function for the elements al and si that corrects for the radiation absorption of the water content in sediment core geob7920 off cape blanc nw africa

correlation frequency of emplacement and source directions of megaturbidites on the madeira abyssal plain abstract this paper describes the sediments of the whole madeira abyssal plain including the madcap area to the south previous studies have centred on the central sub basin which occupies most of the plain and which has become one of the most studied areas of seafloor the plain is made up of a series of large turbidites separated by thin pelagic layers which can be used to provide a high resolution stratigraphy back to about 750 000 years many of the turbidites were deposited close to oxygen isotope stage boundaries suggesting a strong relationship to sea level climate change although the exact initiation mechanism for the flows is not known data from the northern and southern extensions of the plain shows the effects of different entry points for the four main turbidite groups volcanic rich turbidites enter from the ne and e calcareous turbidites from the w one group of organic rich turbidites enters from the se and one group from the ne and e different turbidite sources operate for limited periods before switching to one of the other source areas it is very rare for two sources to provide turbidites at the same isotope stage boundary

origin sedimentary processes and depositional evolution of the agadir turbidite system central eastern atlantic the oligocene to recent agadir turbidite system occurs in the agadir basin abutting against the continental margin off south morocco central eastern atlantic this system is part of the submarine drainage system linking back to the anti and high atlas mountains through the agadir canyon and its sedimentary evolution is shown to comprise lateral shifts of canyon channel overbank and lobe deposits governed by local topography draped palaeorelief seamounts and a contourite ridge and channel avulsions in addition the turbidite system shows an overall retrogradational stacking migrating about 60 km upslope this probably reflects a decrease in gradient on the continental margin gradual basin filling and or a progressive decrease in energy and load of the sediment gravity flows that fed the system the latter change in sediment flux could result from the interplay between the progressive denudation of the source areas together with the climatic change which led to the present arid desertic conditions in the hinterland the seismic features observed with new ultra high resolution seismic tools allow the recognition of the present day sedimentary activity within the agadir turbidite system and this is related among other factors to the active seismicity of the area

the transition zone of the canary current upwelling region abstract like all the major upwelling regions the canary current is characterised by intense mesoscale structure in the transition zone between the cool nutrient rich waters of the coastal upwelling regime and the warmer oligotrophic waters of the open ocean the canary island archipelago which straddles the transition introduces a second source of variability by perturbing the general southwestward flow of both ocean currents and trade winds the combined effects of the flow disturbance and the eddying and meandering of the boundary between upwelled and oceanic waters produce a complex pattern of regional variability on the basis of historical data and a series of interdisciplinary field studies the principal features of the region are described these include a prominent upwelling filament originating near 28 n off the african coast cyclonic and anti cyclonic eddies downstream of the archipelago and warm wake regions protected from the trade winds by the high volcanic peaks of the islands the filament is shown to be a recurrent feature apparently arising from the interaction of a topographically trapped cyclonic eddy with the outer edge of the coastal upwelling zone its role in the transport and exchange of biogenic material including fish larvae is considered strong cyclonic eddies observed throughout the year drift slowly southwestward from gran canaria one sampled in late summer was characterised by large vertical isopycnal displacements apparent surface divergence and strong upwelling producing a fourfold increase in chlorophyll concentrations over background values such intense eddies can be responsible for a major contribution to the vertical flux of nitrogen the lee region of gran canaria is shown to be a location of strong pycnocline deformation resulting from ekman pumping on the wind shear boundaries which may contribute to the eddy formation process

cortex a shipboard xrf scanner for element analyses in split sediment cores abstract the cortex corescanner texel is a non destructive xrf system for the logging of split sediment cores it is a seaworthy instrument that remains active during heavy weather conditions the scanner produces reliable counts for k to sr highly correlated with concentrations measured with atomic absorption spectrometry aas the option to scan al si and elements heavier than sr is in preparation a core section of 1 m can be scanned at 2 cm intervals within an hour a maximum resolution of 1 mm can be achieved at present each region and sedimentary environment requires separate calibration in the nearby future the generator settings will be standardized which may result in the development of a standard calibration procedure because of the high resolution of its semi quantitative records the cortex is a useful tool for detailed time series analysis inter core correlation and shipboard analysis

rock magnetism of late neogene and pleistocene deep sea sediments relationship to sediment source diagenetic processes and sediment lithology we use bivariate scatter plots to illustrate variations in selected rock magnetic properties low field susceptibility anhysteretic and isothermal remanence of late neogene and pleistocene deep sea sediments from 16 sites in the arctic ocean north atlantic equatorial atlantic and north pacific ocean and the arabian sea our intention is to examine the ability of the rock magnetic properties to differentiate the sediments according to factors such as lithology geographical area and the dominant mode of terrigenous sedimentation which at these sites is via ice rafting via bottom currents or via eolian processes overall correlations between sediment magnetic properties and gross lithology is poor and factors such as the source and transport path of terrigenous sediment and detrital magnetic minerals together with the action of reductive diagenetic processes are the major controls on the magnetic properties on the bivariate scatter plots sites with major ice rafted contributions tend to have high sedimentary ferrimagnetic mineral concentrations relatively coarse ferrimagnetic grain sizes and scattered sample point distributions in contrast sites where we infer significant bottom current supply of terrigenous material have tightly grouped sample point distributions carbonate sediments in which the terrigenous component is supplied by eolian processes tend to have a broad range of magnetic mineral concentration caused by glacial interglacial fluctuations in carbonate accumulation and eolian activity sediments containing significant volcanogenic material have high concentrations of relatively coarse grained ferrimagnetic material reductive diagenesis is a significant determinant of sediment magnetic properties in high productivity areas and has the effect of preferentially removing the fine grained ferrimagnetic fraction causing a coarsening of the ferrimagnetic grain size distribution and a rise in the antiferromagnetic ferrimagnetic ratio

sediment dynamics across gravel sand transitions implications for river stability and floodplain recycling data collection was funded through a nerc gcrf building resilience grant ne p015905 1 to h d s and an epsrc gcrf institutional grant ep p510944 1 to m a sampling equipment was lent by ed tipper and bob hilton the rtk gps was loaned from the nerc geophysical equipment facility

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

calibration and application of marine sedimentary physical properties using a multi sensor core logger abstract we examined geophysical data from a multi sensor core logger mscl a logging device providing continuous measurements of gamma ray attenuation p wave travel time and magnetic susceptibility on marine sediment cores in the first part we focused on the gamma ray system and compared two different calibration methods from the gamma ray attenuation we calculated densities and porosities by incorporating mass weighted attenuation coefficients the application of an iteration method reduces the error of the density and porosity estimates compared to grape data in addition we derived equations to calculate water content and dry bulk density from gamma ray attenuation measurements comparison with physical properties determined on discrete samples revealed a very good correlation of both data sets r 0 99 this correlation is valid for sediments from substantially different geological settings e g turbidites hemipelagic muds and opal rich sediments in the second part we applied our data to marine geological questions for sediments from the antarctic polar frontal zone there is indication that the content of biogenic opal can be assessed using a correlation of density and p wave velocity for sediments from the bengal fan the relationship between the mscl acoustic impedance the product of density and p wave velocity and the grain size distribution in discrete samples can be used to predict clay and sand silt ratios for sediment cores from the shelf and upper continental slope

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr