holocene climate optimum and last glacial maximum in the mediterranean the marine oxygen isotope record reconstructions with comprehensive estimates of confidence intervals are presented of changes in the w e stable oxygen isotope gradient in mediterranean surface waters between the holocene climate optimum and the present and between the last glacial maximum and the present rigorous statistical assessment is made of the significances of the mean geographic trends observed in these reconstructions firstly it is concluded that any reconstruction should strictly be based on values obtained by analyses of one single foraminiferal species throughout the basin as different species are found to respond with isotopic variations of different amplitudes to climatic hydrographic change this difference is tentatively related to differences between the habitats and seasons of growth of the various species secondly a significant increase of roughly a factor 3 is found in the mediterranean w e oxygen isotope gradient during the last glacial maximum relative to the present this difference is almost entirely due to increased glacial values in the levantine sea which are considered to be a result of a combination of increased evaporation rates and or somewhat cooler than anticipated surface water conditions thirdly an eastward increase of roughly half the present day magnitude is found for the w e oxygen isotope gradient during the holocene climate optimum values in the levantine sea appear to have undergone up to 0 3 more depletion than those elsewhere in the eastern mediterranean however no significant trends are found between the eastern and western parts of the levantine sea nor between values near the nile delta and those from elsewhere in the levantine sea the holocene climate optimum s eastward increase in the mediterranean oxygen isotope gradient although weaker than the present suggests that the mediterranean continued to function as a concentration basin albeit in a less vigorous way than today finally simple mixing arguments are used to argue that inferred oxygen isotope ratios of surface waters may not be used as an indication of conservative property e g salinity distribution on geological timescales but instead show amplitudes of response to climatic hydrographic changes that likely are 2 times larger than the corresponding amplitudes of response for truly conservative properties

diatom productivity peak and increased circulation during latest quaternary alboran basin western mediterranean abstract diatoms were studied quantitatively in six latest quaternary 70 kyr b p to recent piston cores from the westernmost mediterranean the alboran basin and the atlantic region immediately to the west of the straits of gibraltar the atlantic cores completely lack diatoms in the alboran basin diatoms are common from late stage 3 27 5 kyr b p to termination ib 9 kyr b p and in recent core tops but are absent in the other latest quaternary intervals maximum accumulation of diatoms and highest abundance of species normally in sediments associated with increased productivity occurred during the latest quaternary deglaciation in the first phase of termination i 14 8 kyr b p in the modern alboran basin a region of high biological productivity occurs immediately east of the gibraltar straits this high productivity results from upwelling associated with the interaction between the atlantic inflow and the bottom topography near the spanish coast the upwelled nutrient rich waters are then advected to the east and southeast by the surficial anticyclonic gyral circulation late quaternary variations in diatom abundance are considered to reflect changes in this upwelling intensity with highest diatom abundances inferred to result from increased upwelling associated with an intensification of the anticyclonic gyral circulation highest inferred upwelling rates occurred during the first phase of latest quaternary deglaciation it is possible that an intensification of circulation within the mediterranean basin as a whole occurred from late stage 3 to mid termination i because widespread hiatus formation has been reported at this time in the straits of sicily due to an increase in the formation of intermediate waters diatoms were not preserved in other latest quaternary intervals due to insufficient productivity to counterbalance their dissolution

lake banyoles northeastern spain a last glacial to holocene multi proxy study with regard to environmental variability and human occupation analyses of a 67 m long sediment core from lake banyoles northeastern spain have revealed evidence for the palaeoclimate history of the northern iberian peninsula investigations have included hi

paleoenvironmental changes in the western mediterranean since the last glacial maximum high resolution multiproxy record from the algero balearic basin abstract the present study uses a multiproxy approach in order to further understand the evolution of climate responses in the western mediterranean as of the last glacial maximum sediments from odp site 975 in the algero balearic basin have been analysed at high resolution both geochemically and mineralogicallly the resulting data have been used as proxies to establish a sedimentary regime primary marine productivity the preservation of the proxies and oxygen conditions fluctuations in detrital element concentrations were mainly the consequence of wet arid oscillations productivity has been established using ba excess according to which marine productivity appears to have been greatest during cold events heinrich 1 and younger dryas the s1 time interval was not as marked by increases in productivity as was the eastern mediterranean in contrast the s1 interval was first characterized by a decreasing trend and then by a fall in productivity after the 8 2 ky bp dry cold event since then productivity has remained low here we report that there was an important redox event in this basin probably a consequence of the major oceanographic circulation change occurring in the western mediterranean at 7 7 ky bp this circulation change led to reventilation as well as to diagenetic remobilization of redox sensitive elements and organic matter oxidation comparisons between our paleoceanographic reconstruction for this basin and those regarding other mediterranean basins support the hypothesis that across the mediterranean there were different types of responses to climate forcing mechanism the algero balearic basin is likely to be a key area for further understanding of the relationships between the north atlantic and the eastern mediterranean basins

impact of climate variability in the western mediterranean during the last 20 000 years oceanic and atmospheric responses eolian input fluctuations and paleoceanographic conditions in the western mediterranean have been reconstructed byusing a multi proxyapproach toinferclimate variability for the last 20 000 yr a sediment core from the east alboran sea basin provides high resolution geochemical mineralogical and grain size distribution records from the last glacial maximum onward the accurate chronology obtained closely related with the north greenland ice core project has provided a detailed paleoclimate reconstruction at the centennialemillennial time scale mineral and chemical compositions as well as sediment grain size distribution have been used to establish both fluvial and eolian input variations deep water current intensity and ventilation and productivity conditions at the time of deposition during the cold period greenland stadial 2a the analyzed proxies evidence significant climate oscillations redox proxies showing marked mn al and fe al peaks as well as granulometric parameters support major changes in thermohaline circulation with active circulation triggered by the western mediterranean deep water formation ba al ratios and the presence of authigenic barite point to high productivity during the last heinrich event at this time zr al si al and ti al ratios as well as quartz and palygorskite contents also corroborate dryer conditions in the alboran borderlands with a major reorganization of atmospheric circulation at the beginningof the deglaciationand during the last heinrich event in contrast a decreasing trend in the zr al ratio and increasing mg al k al and illite chlorite kaolinite ratios would indicate enhanced river runoff and supporting lower eolian dust input and wetter periods during the bolling eallerod short term and abrupt climate oscillations such as the intra allerod cold period are likewise reflected by minor yet conspicuous changes in eolian proxies during the younger dryas we distinguish an initialcoldanddryphase withmajorwesterliesintensity thermohalinereactivation andhighproductivity

climate driven changes in sedimentation rate influence phosphorus burial along continental margins of the northwestern mediterranean abstract the burial of phosphorus p in continental margin sediments is a critical component of the marine reactive p budget and thus an important factor in marine biological productivity we determined downcore records of p from a site drilled on the upper slope of the gulf of lions prgl 1 northwestern mediterranean sea changes in total p content were monitored from marine isotope stage mis 6 to mis 11 in addition in two selected intervals 248 277 ka and 306 342 ka the total p record was expanded by adding detailed geochemical analyses of the various p fractions including oxyhydroxide associated p authigenic p detrital p and organic p increased sedimentation rates during glacials owing to seaward migration of the rhone s mouth enhanced the burial of reactive p oxyhydroxide associated authigenic organic phases by decreasing its time at the reactive sediment water interface in turn resulting in increasing proportion of authigenic to detrital phosphorus the inverse was found for interglacial stages the effects of glacial interglacial variation in sedimentation rate over p geochemistry resulted in changes in sediment water interface oxygenation as well as in the efficiency of p burial as shown by c p org and corg preact proxies respectively two events of high p deposition associated with authigenic p formation at 335 ka paut1 and 275 ka paut2 were associated with periods of rapid disintegration of north atlantic ice sheets leading to ice rafted debris ird deposition these high p deposition events appear to be linked to short warm periods that followed cold episodes enhanced continental runoff owing to more humid conditions during short warm episodes could play a critical role for enhanced biogenic productivity and posterior authigenic p accumulation

dansgaard oeschger and heinrich event imprints in alboran sea paleotemperatures past sea surface temperature sst evolution in the alboran sea western mediterranean during the last 50 000 years has been inferred from the study of c37 alkenones in international marine global change studies md952043 core this record has a time resolution of 200 years allowing the study of millennial scale and even shorter climatic changes the observed sst curve displays characteristic sequences of extremely rapid warming and cooling events along the glacial period comparison of this alboran record with 18o from greenland ice greenland ice sheet project 2 core shows a strong parallelism between these sst oscillations and the dansgaard oeschger events five prominent cooling episodes standing out in the sst profile are accompanied by an anomalous high abundance of neogloboquadrina pachyderma sinistral which is confined to the duration of these cold intervals these features and the isotopic record reflect drastic changes in the surface hydrography of the alboran sea in association with heinrich events hl 5

the advection of submesoscale thermal features in the alboran sea gyre abstract noaa 7 infrared and nimbus 7 multi spectral visible imagery of the alboran sea collected as part of the donde va experiment during the period 6 20 october show the advection of submesoscale cold water features about the alboran sea gyre continuous monitoring of thew cold water features using satellite imagery is possible because of the twice daily every 12 h spacing of the noaa 7 coverage of the area after registration to a mercator projection and atmospheric correction analysis of the displacement of the cold water features in successive images shows their apparent origin to be just east of gibraltar their movement at average speeds of 0 4 m s 1 around the gyre and their apparent re entrainment into the incoming atlantic water east of gibraltar the nimbus 7 czcs imagery supplements the analysis by adding details of the movement and the theory on where the cold water features originate during the 15 day period nine cold water features were thermally distinct enough to be tracked for

holocene turbidites record earthquake supercycles at a slow rate plate boundary ongoing evidence for earthquake clustering calls for records of numerous earthquake cycles to improve seismic hazard assessment especially where recurrence times overstep historical records we show that most turbidites emplaced at the africa eurasia plate boundary off west algeria over the past 8 k y correlate across sites fed by independent sedimentary sources requiring a regional trigger correlation with paleoseismic data inland and ground motion predictions support that m 7 earthquakes have triggered the turbidites the bimodal distribution of paleo events supports the concepts of earthquake supercycles and rupture synchronization between nearby faults 13 paleo earthquakes underpin clusters of 3 6 events with recurrence intervals of 300 600 yr separated by periods of quiescence of 1 6 k y without major events on other faults over the study area this implies broad phases of strain loading alternating with phases of strain release our results suggest that fault slip rates are time dependent and call for revising conventional seismic hazard models

oceanographic control of diatom abundances and species distributions in surface sediments of the tropical and southeast atlantic abstract this paper is a descriptive account of the diatomaceous component of pelagic sediments from the tropical and southeast atlantic ocean geographic patterns of diatom abundances whole and fragment forms per gram major species relative abundances and diatom assemblages resolved by q mode factor analysis are presented comparisons drawn to sea surface temperature salinity and productivity distributions suggest that i diatom abundances primarily reflect surface productivity with no apparent dissolution effects due to water depth ii relative abundances of major species vary in their ecologic dependence but do reflect major oceanographic features of the surface waters and iii of the five diatom assemblages resolved four finely delineate the complexity of the low latitude oceanography these assemblages in decreasing order of statistical importance are associated with 1 warm waters of moderate to high primary productivity 2 the oceanward margin of the benguela current a region of high primary production with a maximum in austral summer 3 low salinity waters off the mouths of the zaire and niger rivers and 4 subtropical to tropical waters of lower productivity mostly in the western equatorial atlantic the fifth factor represents the equatorward advection of subantarctic to antarctic diatoms by deep ocean currents

cold water coral growth in the alboran sea related to high productivity during the late pleistocene and holocene abstract cold water corals are common along the moroccan continental margin off melilla in the alboran sea western mediterranean sea where they colonise and largely cover mound and ridge structures radiocarbon ages of the reef forming coral species lophelia pertusa and madrepora oculata sampled from those structures reveal that they were prolific in this area during the last glacial interglacial transition with pronounced growth periods covering the bolling allerod interstadial 13 5 12 8 ka bp and the early holocene 11 3 9 8 ka bp their proliferation during these periods is expressed in vertical accumulation rates for an individual coral ridge of 266 419 cm ka 1 that consists of coral fragments embedded in a hemipelagic sediment matrix following a period of coral absence as noted in the records cold water corals re colonised the area during the mid holocene 5 4 ka bp and underwater photographs indicate that corals currently thrive there it appears that periods of sustained cold water coral growth in the melilla coral province were closely linked to phases of high marine productivity the increased productivity was related to the deglacial formation of the most recent organic rich layer in the western mediterranean sea and to the development of modern circulation patterns in the alboran sea

vs and density structure beneath the colorado plateau constrained by gravity anomalies and joint inversions of receiver function and phase velocity data 1 the colorado plateau is a physiographic province in the western us with an average elevation of 1 9 km where in contrast to neighboring provinces there is little evidence of large scale tectonic deformation or magmatism recent availability of earthscope usarray seismic data allow us to better examine the crust and upper mantle structure beneath the region and test proposed explanations for the plateau s uplift and relative stability using phase velocities for fundamental mode rayleigh waves and p receiver functions we perform over 800 joint inversions for 1 d shear wave velocity vs profiles sampling the plateau and surrounding regions down to 150 km depth we image a sharp change in crustal thickness at the western edge of the colorado plateau with a more gradual increase eastward moving into the rocky mountains a relatively thick 100 km lithosphere beneath the plateau extends into the rocky mountains to the north we use empirical scaling relations to estimate densities from our vs results and predict the associated gravity anomalies which are inconsistent with the observed distribution of the bouguer gravity anomalies we somewhat reconcile the prediction and observations by assuming that lateral density variations below 50 km can be ignored and the lithospheric root is therefore neutrally buoyant while there is some evidence for small scale convection and lithospheric removal at its edges the shape of the lithospheric mantle anomaly is consistent with a large scale uplift of the plateau by heating since removal of the farallon slab we conclude that the lithospheric root is key to the long term stability of the colorado plateau leading to a colder stronger crust

changes in western mediterranean thermohaline circulation in association with a deglacial organic rich layer formation in the alboran sea abstract the accumulation of an organic rich layer orl during the last deglaciation in the alboran sea western mediterranean sea and its link to changes in deep and intermediate water circulation are here investigated benthic foraminiferal assemblages and the shallow infaunal foraminifer uvigerina peregrina 13c record support the establishment of sustained high organic matter fluxes and thus eutrophic conditions at the sea floor during the late phase of the orl younger dryas to early holocene periods since organic matter fluxes were lower mesotrophic conditions during the bolling allerod period they cannot be solely responsible for the orl initiation geochemical sedimentological and micropalaeontological proxies support a major weakening of the deep water convection in the gulf of lion as the main driver for the development of poorly ventilated conditions from intermediate depths 946 m to the deep western mediterranean basin that promoted the beginning of the orl deposition nevertheless a better ventilation at intermediate depths was established during the late orl while the deep basin remained poorly ventilated we propose that our data reflect the arrival of a new better ventilated intermediate water mass analogue to the current levantine intermediate water liw and or a new intermediate water mass from the gulf of lion the ultimate source of this water mass needs to be further explored but chronologies of the changes recorded here indicate that intermediate and deep ventilation phases were decoupled between the western and eastern mediterranean basins during the deglaciation and early middle holocene

high fertility in the alboran sea since the last glacial maximum based on the glacial to postglacial 13c differences between endobenthic uvigerina peregrina species from the alboran basin and from other mediterranean basins changes in the fertility of the western part of this basin during the last deglaciation are reconstructed as a result of particulate organic carbon poc rain from the highly productive upwelling cell along the northwestern margin of the alboran basin u peregrina is presently depleted by about 1 6 with respect to the measured 13c values of bottom water co2 and by about 0 9 with respect to specimens from other areas of the western mediterranean or from the gulf of cadiz within the mediterranean outflow water the uvigerina 13c difference between the alboran sea and the gulf of cadiz 13c was close to 0 at the beginning of the last deglaciation and during the late glacial time this suggests that highly fertile systems set in the alboran sea near 16 kyr b p two rapid increases in the 13c offset are recorded near 15 kyr and 11 kyr b p fluctuations around 1 1 to 1 2 occurred during the early holocene and a maximum was reached near 9 kyr b p after 4 kyr the 13c offset decreased to its present day average value of 0 9 changes in the intensity of surficial production cannot account for all the observed fluctuations especially in the early holocene time a strong decrease in the intermediate and deep water ventilation of the alboran basin may have occurred near 8 9 kyr in phase with the last stagnant phase in the eastern mediterranean and the deposition of sapropel s1 as a result the redistribution and remineralization at depth of the produced organic matter was incomplete the poc rain reaching the sediment was locally intensified and caused the lowering of the 13c values of endobenthic foraminifers such as u peregrina the benthic 13c signal suggests that the difference between the alboran sea and the gulf of cadiz was at its maximum at the same time an important modification in the water masses structure may have occurred near 9 8 kyr b p the deepening of the permanent pycnocline probably related to a thicker atlantic jet at a stage of high sea level stand is recorded by the replacement of the right coiling n pachyderma dominance coincident with a shallow pycnocline by the g inflata dominance coincident with a deep pycnocline diatom abundances were strongly reduced indicating an important modification of the productive system the glacial postglacial evolution of productivity within the alboran basin was therefore more complex than in the adjacent atlantic ocean and opposite to the global one which displays a general increase in productivity during glacial time although it is the global budget of paleoproductivity that would drive the partitioning of carbon within the ocean local or regional discrepancies with the global glacial interglacial model must be addressed local winds and regional atmospheric pressure systems which are the forcing factors for circulation and exchange with the atlantic control the fertile systems of the alboran basin

paleohydrological fluctuations and steppe vegetation during the last glacial maximum in the central ebro valley ne spain combined analysis of sedimentary facies geochemistry and pollen from lake sediment records and sedimentological and palynological studies from slope deposits allow the characterization of vegetation and lake level status during the last glacial lgm in the central ebro valley ne spain these records show the presence of phases of increased effective moisture while regional vegetation was dominated by steppe species the longest lake record comes from la salineta one of the saline lakes in the los monegros area the other lake sequence comes from a sinkhole in the gallego river floodplain the slope deposit from valmadrid is the only periglacial deposit found in the central ebro valley our data indicate that at least for some intervals during full glacial times when cold steppe vegetation dominated the region some lakes experienced more positive water balance than today and run off was also high the data are coherent with the hypothesis that at least for some periods the ice age climate of the western mediterranean was characterized by cold winters with relatively higher effective moisture precipitation minus evaporation ratio and summer droughts increased flow from the pyrenean rivers during the early deglaciation could also have played a significant role in the paleohydrological cycle in the central ebro valley however la salineta records also show evidence for arid periods during glacial times indicating the complex evolution of hydrology and moisture availability in the central ebro valley during the lgm

comparative molecular biomarker assessment of phytoplankton paleoproductivity for the last 160 kyr off cap blanc nw africa abstract we report high resolution molecular abundance data for alkenones dinosterol long chain diols and n alkanols from odp site 658 20 45 n 18 35 w 2263 m water depth these data are compared with previously reported data for toc chlorins opal and long chain n alkanes the contents and mass accumulation rates mars of chlorins are used as total phytoplankton productivity proxies while the contents and mars of opal dinosterol alkenones and diols are used as productivity proxies for diatoms dinoflagellates haptophytes and eustigmatophytes diatoms respectively five high productivity intervals hpis are identified two at the glacial interglacial transition boundaries of 132 122 and 15 8 ka two within the warmer periods of mis 3 50 30 ka and the late holocene 4 0 ka and one within the glacial period of mis 4 67 60 ka productivity was lowest during both the penultimate glacial maximum of mis 6 150 140 ka and the last glacial maximum 22 18 ka as revealed by both the total phytoplankton and individual phytoplankton productivity indicators phytoplankton community structure changed significantly over the last 160 kyr the termination i ii hpis were characterized by higher opal content possibly reflecting increased diatom contributions to total productivity eustigmatophyte diatom and haptophyte contributions were higher during mis 5 but decreased toward the holocene dinosterol revealed an opposite trend with the highest contribution in the holocene we ascribe such changes in phytoplankton communities to the effects brought about by the varying amounts and nature of nutrient inputs contributed regionally by eolian dusts river influxes ocean currents and upwelling water masses

diatom assemblages as upwelling indicators in surface sediments off portugal abstract diatom abundance and assemblage composition have been determined for 169 surface sediment samples from the portuguese margin an area where seasonal upwelling occurs each year from april to october absolute diatom abundance distribution patterns reflect the more intense and or persistent and more homogeneous upwelling north of the nazare canyon the position of the inner upwelling front south of lisbon and the eastern continuation of the coastal upwelling jet along the algarve coast distribution patterns of species and of ecologically defined groups meroplanktonic oceanic freshwater and marine benthic support the hypothesis that diatom species and assemblages are good indicators of the changing character of the upwelling system small species of the genus thalassiosira occur in areas of persistent upwelling where availability of nutrients is more constant and or higher paralia sulcata ehr cleve is an abundant species whose mean cell diameter increases as nutrient availability decreases resting spores mainly of chaetoceros ehrenberg record the position of the zone where higher variability occurs the inner upwelling front

raising the colorado plateau shallow marine rocks exposed on the 2 km high 45 km thick colorado plateau in the western united states indicate that it was near sea level during much of the phanerozoic isostatic calculations however illuminate the difficulty in maintaining a 45 km thick crust at or near sea level we propose that an isostatically balanced 30 km thick proto colorado plateau crust was thickened during the late cretaceous to early tertiary by intracrustal flow out of an overthickened sevier orogenic hinterland this plateau would have been supported by a thick 70 km crustal root which is proposed to have been the source region for hot and weak mid crustal material that flowed eastward from the plateau toward the low elevation proto colorado plateau

climate forcing and neanderthal extinction in southern iberia insights from a multiproxy marine record abstract paleoclimate records from the western mediterranean have been used to further understand the role of climatic changes in the replacement of archaic human populations inhabiting south iberia marine sediments from the balearic basin odp site 975 was analysed at high resolution to obtain both geochemical and mineralogical data these data were compared with climate records from nearby areas baexcces was used to characterize marine productivity and then related to climatic variability since variations in productivity were the consequence of climatic oscillations climate productivity events have been established sedimentary regime primary marine productivity and oxygen conditions at the time of population replacement were reconstructed by means of a multiproxy approach climatic oceanographic variations correlate well with homo spatial and occupational patterns in southern iberia it was found that low ventilation u th high river supply mg al low aridity zr al and low values of baexcess coefficient of variation may be linked with neanderthal hospitable conditions we attempt to support recent findings which claim that neanderthals populations continued to inhabit southern iberia between 30 and 28 ky cal bp and that this persistence was due to the specific characteristics of south iberian climatic refugia comparisons of our data with other marine and continental records appear to indicate that conditions in south iberia were highly inhospitable at 24 ky cal bp thus it is proposed that the final disappearance of neanderthals in this region could be linked with these extreme conditions

eastern mediterranean palaeoclimates from 26 to 5 ka b p documented by pollen and isotopic analysis of a core in the anoxic bannock basin continuous pollen and isotopic records were established for core ban 84 09 gc retrieved from the anoxic bannock basin in the eastern mediterranean on the basis of two 14c dates they document the palaeoclimate between about 25 7 ka b p and 5 2 ka b p in the northern borderlands of the ionian basin the upper half of the core has been redeposited the isotopic record displays a correlation with pollen percentages that is strong and positive for artemisia sage brush and negative for quercus oak the last glacial maximum and the deglaciation are identified by these combined taxa together with chenopodiaceae the glacial maximum around 18 ka b p which has elsewhere been dated from 20 to 15 ka b p has pollen percentages that are high for artemisia and low for quercus the climate in the pollen source area was arid cold in winter briefly warm in summer and sustained the vegetation of a semi desert the onset of deglaciation after 18 ka b p coincides with that of the decline in artemisia pollen percentage however this decline does not indicate reduced aridity because it is accompanied by a pollen percentage rise of the even more arid herbs chenopodiaceae and ephedra throughout the deglaciation from 18 to 11 ka b p the aridity progressively increases culminating at 11 ka b p this trend is briefly interrupted by a more humid event shown by a peak in artemisia pollen percentage and a smaller peak in oak these two peaks are coeval with the bolling allerod chronozone 13 11 ka b p maximum aridity occurs during the younger dryas chronozone 11 10 ka b p afterwards the oak pollen percentage begins a steady increase and its maximum value is coeval with the lowest isotopic value dated at 8760 170 yr b p this period was one of high moisture warm summers and according to altitude mild to cool winters this climate sustained forests that were mediterranean in the lowlands and warm temperate in the uplands a high pollen concentration is observed during this period and reveals the presence of sapropel s1 which is otherwise unrecognizable in this entirely black core during the following period between 8760 170 and 5200 yr b p the 180 reverts to slightly higher values and the quercus pollen percentage decreases while the pollen percentage of the wetter ostrya the oriental hornbeam increases the high pollen concentration during the deposition of sapropel s1 cannot have been caused by increased pollen input into the sea this pollen being wind borne nor by increased pollen production for all taxa both trees and herbs we conclude that it is entirely due to increased preservation of this allochtonous organic material by the deep anoxia of the bottom water below a thick anoxic water column the coincidence of sapropel deposition with warm and humid local climate as well as with the second global meltwater pulse suggests that the cessation of bottom water ventilation was due to decreased surface water density resulting from less saline incoming atlantic surface water increased local runoff and warmer winters

increased upwelling off portugal during the last glaciation diatom evidence abstract quantitative studies have been carried out on opaline microfossils and diatom assemblage composition and preservation in two latest quarternary 100 ka to p d cores from the continental slope of portugal the sites are located in an area of modern summer coastal upwelling created by northerly trade winds the spatial patterns and intensity of this upwelling system are accurately recorded by the diatom abundances and taxonomic composition in the surface sediments the diatom record in these sequences indicates that coastal upwelling intensity was similar to present day during late holocene interglacial stage 3 and late stage 5 higher during stage 2 and lower in the early holocene paleoproductivity estimates are consistent with the diatom accumulation rates from stage 3 to the recent this indicates that both the diatom and the organic carbon content of the sediments mainly reflect the biological productivity in the euphotic zone

ocean surface water response to short term climate changes revealed by coccolithophores from the gulf of cadiz ne atlantic and alboran sea w mediterranean the response of coccolithophore assemblages to short term millennial and centennial climatic changes over the last 50 kyr is studied in core m39029 7 from the gulf of cadiz atlantic ocean and core md95 2043 from the alboran sea western mediterranean sea the nannoplankton data are compared with oxygen isotopes u37k sst and other biogeochemical and sedimentological proxies to obtain a new perspective of the paleoceanography and paleoecology of the area during these short term climatic changes coccolithophores indicate that heinrich events he were characterised by the presence of cold low salinity and turbid water masses on both sides of the strait of gibraltar high abundances of the lower photic zone lpz species florisphaera profunda in the gulf of cadiz synchronous with he are interpreted as being an evidence of upper water column stratification on the atlantic side these episodes coincided with input of terrigenous material especially during h2 surface waters during dansgaard oeschger do stadials were also cold and turbid while most of do interstadials were characterised by warm water flora the increase in small placoliths small gephyrocapsa and emiliania huxleyi 4 m which is considered here as a cold water indicator the sharp decrease in large specimens of e huxleyi related to the warming trend in the last deglaciation can be used as a biostratigraphic reference level that marks at least approximately the deglaciation and the beginning of the holocene peaks of f profunda are observed during termination 1 t1 in the alboran sea they are isochronous with the organic rich layer 1 recognised in the western mediterranean in this interval the water column of the region was stratified as a consequence of the global increase in the sea level following the deglaciation quantitative analyses of the coccolithophore assemblage allow us to interpret that coccolithophore production has been higher in the alboran sea than in the gulf of cadiz during the holocene

holocene climate variability of the western mediterranean surface water dynamics inferred from calcareous plankton assemblages a high resolution study centennial scale has been performed on the calcareous plankton assemblage of the holocene portion of the ocean drilling program site 976 alboran sea with the aim to iden

crust and mantle structure across the basin and range colorado plateau boundary at 37 n latitude and implications for cenozoic extensional mechanism we present new evidence on the seismic velocity and density of the crust and upper mantle along a 200 km long transect across the eastern basin and range and western colorado plateau at 37 n latitude receiver functions computed from the p waveforms recorded with 10 portable broadband stations deployed along the transect were used to estimate crustal thickness variations the crust is 30 35 km thick within the eastern basin and range and increases over a distance of 100 km at the western edge of the colorado plateau reaching a maximum of approximately 45 km east of the hurricane fault the timing of crustal multiples within the reciever functions were used to estimate the v p v s of the crust along the profile and we found that the western colorado plateau crust is characterized by a high poisson s ratio 0 28 0 29 indicative of a crust with an average mafic composition we estimated the upper mantle lid thickness along our profile based on teleseismic p wave travel times and constraints provided by gravity data our data and available geophysical constraints are most consistent with a lithosphere that thickens from an average thickness of 60 km beneath the basin and range to 100 km beneath the western colorado plateau although the basin and range lithosphere may have significant thickness variations the thick strong mafic crust and thicker mantle lid under the colorado plateau can account for the relative geologic stability and subdued magmatism of the plateau during laramide compression and cenozoic extension compared to surrounding regions the crustal and lithospheric thinning across the tectonic boundary occurs over a short distance 100 km suggesting it is a geologically young feature produced by a predominantly mechanical response to late cenozoic extension our new lithosphere model at 37 n latitude is consistent with the existence in early cenozoic time of a flat subducted slab at 100 km depth and a relict sevier laramide 50 60 km thick crustal welt and 60 100 pure shear extension values of 1 6 2 0 during the late cenozoic

coccolithophore productivity and surface water dynamics in the alboran sea during the last 25kyr abstract coccolithophore productivity and surface water dynamics for the last 25 kyr in the alboran sea western mediterranean are described in a study of high resolution sedimentary records from two cores her gc t1 and ceuta10pc08 whose locations are currently characterized by different hydrographic conditions fossil coccolithophore assemblages and oxygen isotopes and alkenone and planktonic foraminifera derived sea surface temperature sst records allowed a reconstruction of the properties of the inflowing atlantic water aw which have proved to be a primary control of the variations in productivity in the neighborhood of the strait of gibraltar other local factors such as fluvial discharge wind induced and eddy induced upwelling are proposed to have influenced marine productivity in more distant areas the entrance of cold and less saline aw during the stadials associated with heinrich events 2 and 1 prevented primary productivity which increased along the last glacial maximum probably due to a greater fluvial discharge during terminations 1a and 1b the upper water column was affected by stratification although wind induced upwelling occurred locally the bolling allerod was characterized by a gradual increase in productivity and the development of the organic rich layer two phases of the younger dryas are recognized a first phase which was colder followed by a second phase which was warmer and wetter differences in productivity between both locations during these two phases can be attributed to fluvial discharge and the changing properties of the aw local hydrography such as the dynamics of the western anticyclonic gyre gained greater importance in determining productivity and its variations during the holocene which was the most productive period

the atlantic inflow in the western alboran sea abstract an extensive dataset collected in the alboran sea during the 1982 donde va experiment is used to characterize the kinematics and dynamics of the inflow of atlantic water into the mediterranean sea the veering of the inflow toward the ene after leaving the strait of gibraltar and the existence of an anticyclonic gyre that fills much of the western alboran sea in the upper 200 m are confirmed in the mean inflow variability with periods of 2 to 10 days is described particularly striking is one interval of about 9 days during which the gyre was not present and the inflow adopted a southerly course after leaving the strait the observations are interpreted in terms of vorticity conservation and in the light of earlier theoretical and numerical results

first record of middle miocene marine diatoms from the colombian pacific nw south america and their paleoceanographic significance abstract middle miocene marine diatoms have been reported in the eastern equatorial pacific by the deep sea drilling project dsdp the ocean drilling program odp and the integrated ocean drilling program iodp few studies however have been completed on onshore sections from south america vallejo et al 2006 published the biostratigraphy of the ladrilleros juanchaco section on the northwest pacific colombian coast utilizing calcareous nannofossils planktonic foraminifera and diatoms in this work we present in detail the study of marine diatoms of that section in order to understand their implications with the age model proposed and provide a paleoceanographic interpretation the diatom recovery is restricted to two intervals at the top of the miocene sequence two biozones from the low latitude zonation can be recognized from base to top they are 1 the coscinodiscus lewisianus zone which contains the same species assemblage reported in antofagasta coastal sediments chile and 2 the craspedodiscus coscinodiscus zone we found that the diatoms represent older ages than proposed by calcareous nannofossils these different ages suggest diachronism between the events of microfossil groups nevertheless in a new interpretation of the distribution patterns of calcareous nannofossils in the upper part of the section the diatom age model could be synchronous the high abundance of thalassionema nitzschioides and thalassiothrix longissima reveal cool upwelling rich oceanic waters at the top of the sequence as well as an increase in paleoproductivity suggested by an increase of rhizosolenia spp and t longissima mats cool water trends support a strengthening of the peru chile current actinoptychus sp leptocylindrus danicus and paralia sulcata point to a nearshore environment the common occurrence of fresh water continental diatoms and palm silicophytoliths indicate an increased input of continental material since ichnofossils and benthic foraminifera reveal ocean depths below 1000 m this change may have related to hyperpycnal flows

an environmental snapshot of the bolling interstadial in southern iberia the bolling allerod interstadial is the closest warm time period to the holocene the study of the climate variability during this most recent warm scenario provides a natural record of potential environmental changes related with global temperature variations little is known about this interstadial in the southern iberian peninsula therefore the exceptional climatic record of the otinar paleo lake ca 14 5 14 0 cal ka bp provides environmental information about the first part of this interstadial bolling in this key region although the studied high resolution isotopic record point to almost invariant hydrological conditions in the paleo lake with little change in the carbon budget and important limestone dissolution the pollen record shows an increase in forest species that can be interpreted as a warming trend and an increase in humidity during the bolling in the area this record is one of the few continental archives that show this climatic trend in southern iberia agreeing with many other regional records from the western mediterranean this does not agree with higher latitude records that show an opposite trend this opposite pattern in precipitation between the western mediterranean and more northern latitudes could be explained by a persistent and increasing negative nao mode during the bolling in this area

proliferation and demise of deep sea corals in the mediterranean during the younger dryas abstract uranium series and radiocarbon ages are reported for deep sea corals madrepora oculata desmophyllum dianthus lophelia pertusa and caryophyllia smithii from the mediterranean sea u series dating indicates that deep sea corals have persisted in the mediterranean for over 480 000 years especially during cool interstadial periods the most prolific period of growth however appears to have occurred within the younger dryas yd period from 12 900 to 11 700 years bp followed by a short 330 years phase of post yd coral growth from 11 230 to 10 900 years bp this indicates that deep sea corals were prolific in the mediterranean not only during the return to the more glacial like conditions of the yd but also following the rapid deglaciation and transition to warmer conditions that followed the end of the yd surprisingly there is a paucity last glacial maximum lgm coral ages implying they were largely absent during this period when cold water conditions were more prevalent radiocarbon ages show that the intermediate depth waters of the mediterranean generally had 14 c compositions similar to surface waters indicating that these waters were extremely well ventilated the only exception is a narrow period in the yd 12 500 100 years bp when several samples of lophelia pertusa from the ionian sea had 14 c values falling significantly below the marine curve using a refined approach isolation ages isol of 300 years to 500 years are estimated for these intermediate 800 1000 m depth waters relative to surface marine waters indicating a reduction or absence of deep water formation in the ionian and adjacent adriatic seas during the yd contrary to previous findings we find no evidence for widespread intrusion of low 14 c atlantic waters into the mediterranean prolific growth of deep sea corals in the mediterranean ended abruptly at 10 900 years bp with many of the coral bearing mounds on the continental slopes being draped in a thin veneer of mud their demise is attributed to a number of factors including the direct loss of habitat due to high sedimentation that accompanied glacial meltwater pulses together with rising temperatures that would have finally pervaded the deeper water of the mediterranean following the onset of holocene warming

deep sea circulation in the alboran sea alboran sea circulation between 220 and 1100 m depth is studied interaction between three types of water masses in this area causes a complicated flow pattern atlantic water flowing as a jet through the strait of gibraltar into the mediterranean often forms an anticyclonic gyre to the depth of 200 m and its features are now well documented a few works based on geostrophic calculations and bernoulli s equation treat the deep flow nine free floats were released at different depths and locations from january to may 1982 and acoustically tracked every 2 hours for 40 to 90 days acoustical tracking was done from three listening stations moored in the area the tracks of the floats at all depths from 220 to 1100 m revealed broad and slow approximately 2 5 cm s cyclonic circulation located under the surface anticyclonic gyre part of the flow following the bottom topography turned near the moroccan continental slope as a jet approximately 5 cm s to gibraltar and part turned to the east following the southern boundary of the deep channel to the isle of alboran

planktonic response to main oceanographic changes in the alboran sea western mediterranean as documented in sediment traps and surface sediments abstract in order to determine the influence of seasonal oceanographic changes to the export of particulates and the flux of organisms as well as its corresponding integrated signal left in the bottom sediments of the alboran sea western mediterranean two mooring lines alb 1f and alb 1d were deployed from july 1997 to may 1998 on the continental slope south of malaga at 36 01 n 04 16 w and 36 14 n 04 28 w and a water depth of 1004 and 958 m respectively the mooring locations are under the influence of the incoming atlantic surface water asw at the northern and productive edge of the western alboran gyre wag and of the wind induced upwelling offshore the spanish coast additionally a total of five core tops located in the same area were studied the results are compared to information based on seawifs images of chlorophyll a concentration sst meteorological data on wind direction and intensity and fluvial discharges from the main rivers of the alboran basin the temporal oceanographic evolution of the alboran sea during the studied period was divided into five episodes e1 july 1997 e2 august october 1997 e3 november to mid december 1997 e4 december march 1998 and e5 april may 1998 the episodes represent different oceanographic conditions in the alboran sea during the studied period detailed analyses of the recorded pattern of bulk components calcareous nannoplankton planktonic foraminifera diatoms and phytoliths reflect seasonal changes in the main hydrographic regimes in the western alboran sea all biogenic bulk components as well as the annual evolution of the floral and faunal assemblages follow a tri modal pattern with maximum fluxes recorded during e1 e3 and e5 representing periods of higher productivity and wind induced upwelling during these periods species such as the small gephyrocapsa group gephyrocapsa muellerae and calcidiscus leptoporus the foraminifer globigerina bulloides and the diatom chaetoceros resting spores rs were dominant gephirocapsa oceanica and globorotalia inflata were coupled to the evolution of the atlantic surface water asw or related to surface water stability e2 and e4 the diatom leptocylindrus danicus responded to upwelling relaxation and water stratification e1 e2 and e4 and benthic diatoms were related to eddy intensity at bottom phytolith fluxes were directly related to wind intensities and the prevailing westerly winds e3 and e5 the distribution of microfossils in surface sediments differs from the biogenic assemblages recorded in the sediment traps in this sense during 1997 1998 the strongest el nino event in the last century took place which could have forced an unusual seasonality in the alboran sea reflecting an exceptional micropaleontological signal not observed in the surface sediments

eolian evidence for spatial variability of late quaternary climates in tropical africa abstract study of the eolian fraction of late quaternary sediments from the tropical atlantic reveals that two modes of long term climate variability have existed in tropical africa during the last 150 000 yr tropical northwest africa i e the southwestern sahara and sahel was driest during glaciations and stades but wetter than at present during interglaciations and interstades this may be a response to ice sheets at higher latitudes via equatorward displacement of the westerlies and the subtropical high in contrast central equatorial africa southeast of the sahara was most arid during interstades and times of ice growth and most humid during deglaciation wet periods in this area correspond to insolation maxima in northern hemisphere summer a 23 000 yr precessional rhythm is suggested supporting a direct link between african monsoon intensity and orbitally modulated insolation the late holocene is the only time observed when both areas are arid during an interglacial episode this may reflect in part anthropogenic disturbance of late holocene climates

a simple criterion for gyre formation by the surface outflow from a strait with application to the alboran sea a survey of relevant numerical laboratory and observational studies combined with our own laboratory experiments suggests that the surface outflow from a strait generally forms a gyre in the adjacent sea if the exit corner is sharp the gyre grows from an initial separation bubble of radius u f where u is the current speed and f the coriolis frequency the criterion for the maintenance of a coastal jet along a curved coast instead of separation and gyre formation seems to be that the rossby number u frw 1 1 with rw the radius of curvature of the exit corner so that the coriolis force can hold the current to the coast this synthesis disregards factors such as the variation of u across the current but applied to the flow through the strait of gibraltar into the alboran sea suggests that a gyre should always form as the exit corner is sharp we suggest though that the relevant curvature is that where the interface between the two layers intersects the seafloor rather than where the sea surface meets the coast if this is the case supercritical flow or some subcritical flows at the eastern end of the strait should still always lead to gyre formation but the observed replacement of the gyre by a coastal jet along the moroccan coast could be related to subcritical flow that is reduced below its normal value by a barotropic fluctuation or by changes in the interface depth in the mediterranean

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

pliocene atlanto mediterranean biogeography of patella pellucida gastropoda patellidae palaeoceanographic implications abstract patella pellucida is a north western atlantic shallow water grazing gastropod typically living and feeding on laminarian algae it is an upper cenozoic species known from the icelandic and iberian pliocene to recent today the species is usually considered to be primarily a northern cooler water species inhabiting the atlantic coasts of europe but rarely found off the atlantic nw african coast and westernmost mediterranean its presence in the warm subtropical to tropical pliocene atlantic and mediterranean iberian waters is thus unexpected p pellucida lives on laminarian algae which occur in cold or temperate nutrient rich ocean waters at higher sea surface temperatures laminarian algae become physiologically stressed and are found only where seasonal upwelling of cooler nutrient rich waters occurs such oceanographic conditions exist today e g off the western coast of iberia it is suggested that similar upwelling conditions were already in place in western iberia and in the alboran sea during pliocene times and that the distribution of p pellucida was dictated by upwelling of nutrient rich cooler waters and high productivity conditions rather than sea surface temperature alone thus the unexpected pliocene geographic distribution of p pellucida demonstrates that high productivity associated with upwelling may at least in the atlanto mediterranean area override the dominant biogeographic pattern resulting from the latitudinal sea surface temperature gradient of water masses

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

paleoproductivity variations related to climatic conditions in the alboran sea western mediterranean during the last glacial interglacial transition the diatom record the present study addresses the analysis of changes in marine primary productivity derived from climatic variability over the last 30 000 yr the study area is the alboran sea this is the westernmost basin of the mediterranean sea and was a very sensitive area to changes in sea levels and atmospheric configuration during the last glacial interglacial transition we report the results from four sediment cores recovered in both the western and eastern alboran basins this allowed us to monitor the w e evolution of the hydrological structures the study is mainly based on the diatom record although total organic carbon toc isotopes and uk 0 37 sst were also used to gain further information paleoceanographic conditions favoured high paleoproductivity rates during the last glacial maximum although this occurred at termination 1a and during the younger dryas event yd increasing towards the easternmost sites during these periods meteorological conditions with increased westerlies intensified the flow to the east driving an eastward migration of the western anticyclonic gyre a possible displacement of the north alboran upwelling system is also considered the major component of the diatom assemblage during the yd are the resting spores of leptocylindrus danicus which suggest the presence of cooler and less saline surface waters the opposite behaviour between planktonic and benthic proxies in addition to the high toc values allows us to infer a phase of reduced deep water renewal between 16 5 and 9 cal ky bp fresh water diatoms and opal phytoliths were used as indicators of aridity and humid land conditions respectively during the glacial period and until 14 cal ky bp we observed a gradual climatic deterioration accompanied by a loss of grass belts climatic conditions were warmer and moister during the bolling allerod while the yd was dry the re establishment of vegetation belts and replenishment of lakes was observed at 8 cal ky bp q 2001 elsevier science b v all rights reserved

the greenland ice sheet project 2 depth age scale methods and results the greenland ice sheet project 2 gisp2 depth age scale is presented based on a multiparameter continuous count approach to a depth of 2800 m using a systematic combination of parameters that have never been used to this extent before the ice at 2800 m is dated at 110 000 years b p with an estimated error ranging from 1 to 10 in the top 2500 m of the core and averaging 20 between 2500 and 2800 m parameters used to date the core include visual stratigraphy oxygen isotopic ratios of the ice electrical conductivity measurements laser light scattering from dust volcanic signals and major ion chemistry gisp2 ages for major climatic events agree with independent ages based on varve chronologies calibrated radiocarbon dates and other techniques within the combined uncertainties good agreement also is obtained with greenland ice core project ice core dates and with the specmap marine timescale after correlation through the 18 o of o 2 although the core is deformed below 2800 m and the continuity of the record is unclear we attempted to date this section of the core on the basis of the laser light scattering of dust in the ice

imaging crustal and upper mantle structure beneath the colorado plateau using finite frequency rayleigh wave tomography a new 3 d shear velocity model of the crust and upper mantle beneath the colorado plateau and surrounding regions of the southwestern united states was made with finite frequency rayleigh wave tomography using earthscope usarray data the goal of our study is to examine the colorado plateau lithospheric modification that has resulted from cenozoic tectonism and magmatism we have inverted for the isotropic vs model from a grid of rayleigh wave dispersion curves obtained by a modified two plane wave method for periods from 20 to 167 s we map the lithosphere asthenosphere boundary under the colorado plateau by identifying the middle of the shallowest upper mantle negative vs gradient the depths of the lithosphere asthenosphere boundary inferred here agree well with receiver function estimates made independently the strong lateral heterogeneity of shear velocity can be mainly attributed to 200 400 k variations in temperature together with 1 partial melt fraction in the shallow upper mantle the resulting vs structures clearly image the upper mantle low velocity zones under the colorado plateau margins that are associated with magmatic encroachment these upper mantle low velocity zones resulted from the convective removal of the colorado plateau lithosphere that had been rehydrated by subduction released water refertilizing and destabilizing it this convective erosion by the asthenosphere at the low viscosity part of the lithosphere is driven by the large step in lithospheric thickness and the thermal gradient across the boundary between the plateau and the extended basin and range since the mid cenozoic at a rate similar to that of magmatic migration into the plateau from the southeast south and northwest moreover the rayleigh wave tomography model images parts of a high velocity drip in the western colorado plateau and thus provides additional seismic evidence for ongoing convective downwelling of the lithosphere that was initially suggested by receiver functions and body wave tomography the widespread edge convective erosion which the regional delamination style downwelling processes are a 3 d manifestation of could provide additional buoyancy sources to support the excess uplift at the margins of the plateau

late glacial to recent deep sea benthic foraminifera from the northeastern atlantic cadiz gulf and western mediterranean alboran sea paleooceanographic results abstract deep sea benthic foraminifera of the region of water exchange between the mediterranean and the atlantic ocean at the gibraltar strait show significant water mass relationships for the past 18 000 years cores used in this benthic foraminifera analysis were selected according to the context of the distribution of various deep bottom water masses on each side of the gibraltar strait 1 1 on the atlantic side of the strait two cores ks 8228 ks 8229 are located in the present day nadw and one kc 8221 in the upper part of the present mediterranean outflow water 2 2 on the mediterranean side of gibraltar two cores kc 8241 su 8107 are located in the deep water mass and one ks 8230 in the intermediate water mass in the two deep basins 1500 2800 m depth in the gulf of cadiz 1200 1300 m depth in the alboran sea the paleooceanographic changes appear to be in an opposite way for the past 18 000 years the alboran basin shows a paleooceanographic evolution from a well oxygenated nutrient rich environment at about 18 000 yr b p to a nutrient poor oxygen depleted environment from 13 000 to the present time moreover for the time span synchronous with the well known development of sapropels in the eastern mediterranean basins between 10 000 and 7000 yr b p the faunal assemblage shows most unusual characteristics implying drastic environmental conditions conversely in the gulf of cadiz the environment pass as from a biotope occupied by an oxygen depleted nutrient poor water mass at about 18 000 years b p to a biotope occupied by nadw since the younger dryas this agrees with previous data obtained in the northeastern atlantic ocean caralp 1987 in the epibathyal zones 550 800 m depth on both sides of the gibraltar strait paleohydrographic changes do not seem so important according to the present and very late holocene assemblages which are similar on both sides of the strait with a strong east west flow two other stratigraphic episodes have shown the same conditions of water exchanges the end of the isotopic stage 2 and the younger dryas conversely during the last glacial maximum the bolling allerod and the lower holocene westward water fluxes were probably lower at no time the hypothesis of a reversal or a stop in the east west exchanges between mediterranean and atlantic ocean may be justified

neogene sapropels in the mediterranean a review for 50 years the existence of sapropels organic carbon rich sediments deposited within plio pleistocene sediments of the mediterranean sea has been known initially research concentrated on material recovered in relatively short gravity piston cores taken from the eastern basins where sequences were found to be well developed preserved and had extensive spatial coverage in the main previous studies concentrated upon establishing a workable stratigraphy spatial correlation of individual layers and determining the probable depositional mechanisms however despite a plethora of research papers some issues still remain unresolved this is in part due to a lack of agreement between investigators sampling and analytical short comings restricted sample size and the fact that in many instances like was not being compared with like recently the limit of sapropels in the western basin has been further extended as a result the palaeoceanographic palaeoclimate models which had previously been developed for deposition of sapropels in the eastern basin have been modified most recently strong links have been established between astronomical cyclicity and sapropel formation this review paper provides a summary of sapropel research to date and ongoing sapropel research in the mediterranean some of which appears in this thematic issue of marine geology it is fitting that this thematic issue of marine geology be dedicated to the memory of colette vergnaud grazzini and rob kidd who in many ways helped to initiate the resurgence in sapropel studies in the 1970s in the mediterranean perhaps in 50 more years we will know all of the answers 1999 elsevier science b v all rights reserved

through thick and thin a new model for the colorado plateau from seismic refraction data from pacific to arizona crustal experiment we have constructed a model for the crust and uppermost mantle beneath the colorado plateau by combining newly acquired seismic refraction wide angle reflection data from the 1989 pacific to arizona crustal experiment pace cross profile with data collected by roller 1965 a combination of forward modeling methods was used to model travel times and relative amplitudes of crustal and upper mantle phases the salient features of the model for the colorado plateau hereafter referred to as the plateau are 1 an upper crust having an average velocity of 6 1 km s with a low vertical velocity gradient 2 midcrustal discontinuities at depths of 30 to 38 km beneath the plateau 3 a lower crust that varies in thickness 5 to 16 km and has an average velocity of 6 8 km s 4 a transitional lower crust upper mantle boundary and 5 a crustal thickness of 45 3 km a comparison of our new model for the colorado plateau with recent models for the basin and range shows that the upper crusts of the two provinces are similar but that the lower crust of the plateau is thicker particularly in the plateau s central region these observations are consistent with the idea that the basin and range could have formed from crust like that of the colorado plateau

a new perspective of the alboran upwelling system reconstruction during the marine isotope stage 11 a high resolution coccolithophore record abstract a high resolution study of the mis 12 mis 11 transition and the mis 11 430 376 kyr coccolithophore assemblages at ocean drilling program site 977 was conducted to reconstruct the palaeoceanographic and climatic changes in the alboran sea from the variability in surface water conditions the nannofossil record was integrated with the planktonic oxygen and carbon stable isotopes as well as the uk 37 sea surface temperature sst at the studied site during the investigated interval the coccolithophore primary productivity reconstructed from the ppp primary productivity proxy absolute values of gephyrocapsa caribbeanica small gephyrocapsa group revealed pronounced fluctuations that were strongly associated with variations in the intensity of the regional alboran upwelling system the comparison of the nannoplankton record with opal phytolith content for the studied site and the already available pollen record at the nearby integrated ocean drilling program site u1385 suggests an association of the upwelling dynamics with the variability of the north atlantic oscillation like nao like phase high ppp during positive nao like phases is the result of intensified upwelling owing to the complete development of the surface hydrological structures at the alboran sea this scenario was identified during the mis 12 mis 11 transition 428 422 kyr the late mis 11c 405 397 kyr and mis11 b to mis 11a 397 376 kyr two short term minima in the ppp and sst were observed during mis 11 b and were coeval with the north atlantic heinrich type ht events ht3 390 kyr and ht2 384 kyr increased abundance of the subpolar coccolithus pelagicus subsp pelagicus and gephyrocapsa muellerae was consistent with the inflow of cold surface waters into the mediterranean sea during the ht events lowered ppp during negative nao like phases is the result of moderate upwelling by the incomplete development of surface hydrological structures at the alboran sea this scenario is expressed during the early mis 11c 422 405 kyr overall the results of our study provide evidence of the important role of atmospheric circulation patterns in the north atlantic region for controlling phytoplankton primary production and oceanographic circulation dynamics in the western mediterranean during mis 11

high frequency climate fluctuations over the last deglaciation in the alboran sea western mediterranean evidence from calcareous plankton assemblages abstract a high resolution study with a centennial scale resolution has been performed on the calcareous plankton assemblage coccolithophores and planktonic foraminifera at ocean drilling program site 976 alboran sea western mediterranean focusing on the interval between 20 and 9 ka in order to reconstruct changes in surface and subsurface water dynamics and productivity the biotic surface water proxies integrate the extremely detailed multi decadal scale geochemical data set and the pollen record already available at the core thus providing a complete paleoenvironmental paleoceanographic reconstruction the results highlight the sensitivity of the calcareous plankton in recording stadial interstadial phases and higher frequency climatic events that produced changes in sea water features wind induced upwelling and river discharge during the last glacial period favored nutrient availability and moderate productivity during heinrich stadial 1 hs1 the arrival of cold and fresher waters from iceberg melting in the north atlantic significantly hampered productivity at its lowest values of the whole investigated interval calcareous plankton behavior supports the hypothesis that hs1 is a composite event marked by three phases hs1a characterized by the coldest sst polar atlantic water inflow into the basin and a first step toward a dry climate on the continent hs1b recording enhanced freshwater inflow and drought on land and hs1c indicating reduced polar water influx the bolling allerod ba interstadial sees the highest rate of productivity in the entire interval and accompanies the deposition of organic rich layer 1 during the ba coccolithophore assemblage also marks higher frequency changes in hydrographic conditions apparently in relation with greenland interstadial i gi i high variability the younger dryas stadial yd is characterized by refunding cold and dry conditions although not as severe as during hs1 and by enhanced detrital input in surface water during drier conditions on land the holocene onset records climate amelioration both in the marine and continental environment although coccolithophore productivity is not as high as during the ba the rapid shifts in climate sensitive taxa support the hypothesis that each of the climate phases subphases is characterized by a complex pattern forced by strong interaction between ice sheet instability meltwater discharge entering the gibraltar strait north atlantic westerlies and moisture availability clearly impacting over surface water temperature productivity and land masses

lithospheric dismemberment and magmatic processes of the great basin colorado plateau transition utah implied from magnetotellurics 1 to illuminate rifting processes across the transition zone between the extensional great basin and stable colorado plateau interior we collected an east west profile of 117 wideband and 30 long period magnetotelluric mt soundings along latitude 38 5 n from southeastern nevada across utah to the colorado border regularized two dimensional inversion shows a strong lower crustal conductor below the great basin and its transition zone in the 15 35 km depth range interpreted as reflecting modern basaltic underplating hybridization and hydrothermal fluid release this structure explains most of the geomagnetic variation anomaly in the region first measured in the late 1960s hence the transition zone while historically included with the colorado plateau physiographically possesses a deep thermal regime and tectonic activity like that of the great basin the deep crustal conductor is consistent with a rheological profile of a brittle upper crust over a weak lower crust in turn on a stronger upper mantle jelly sandwich model under the incipiently faulted transition zone the conductor implies a vertically nonuniform mode of extension resembling early stages of continental margin formation colorado plateau lithosphere begins sharply below the western boundary of capitol reef national park as a resistive keel in the deep crust and upper mantle with only a thin and weak moho level crustal conductor near 45 km depth several narrow steep conductors connect conductive lower crust with major surface faulting some including modern geothermal systems and in the context of other great basin mt surveying suggest connections between deep magma sourced fluids and the upper crustal meteoric regime the mt data also suggest anisotropically interconnected melt over a broad zone in the upper mantle of the eastern great basin which has supplied magma to the lower crust consistent with extensional mantle melting models and local shear wave splitting observations we support a hypothesis that the transition zone location and geometry ultimately reflect the middle proterozoic suturing between the stronger yavapai lithosphere to the east and the somewhat weaker mojave terrane to the west we conclude that strength heterogeneity is the primary control on locus of deformation across the transition zone with modulating force components

accumulation rates of major constituents of hemipelagic sediments in the deep alboran sea a centennial perspective of sedimentary dynamics the accumulation rates of sediment and major constituents in three different geographic areas of the alboran sea have been assessed by means of 210pb and 137cs concentration profiles mixing is present in the top layer of the sedimentary column with mixing coefficients estimated to range from 0 2 to 15 cm2 yr 1 overall apparent sedimentation rates for the last 100 years range from 0 014 to 0 182 g cm 2 yr 1 and show a tendency to decrease with distance to the coast and water column depth however specific characteristics of the sea floor for each physiographic environment govern the actual patterns of sediment accumulation particularly noticeable are the feeding role of submarine canyons the trapping effect of slope terraces and the isolation caused by ridges sediment accumulation induced by turbiditic flows is also observed north of the almeria oran area excess 210pb inventories and surface concentrations reveal a net effect of sediment focussing and point to the role of bottom nepheloid layers in supplying a significant fraction of sediments to the deep areas this is also evidenced by comparison of bottom sediment with the sediment trap data available from the malaga area we estimate that the particle advective input below 30 m above the bottom accounts for as much as 50 70 of the material that is ultimately deposited onto the sea floor the greater abundance of lithogenic material in the malaga zone 80 reflects its larger input in the western alboran sea conversely carbonate contents increase from less than 20 in this area to about 30 in the almeria oran zone reflecting the lesser importance of the dilution by lithogenic components biogenic silica was only detected in some surface samples and no significant preservation was observed below the eh boundary abundance and accumulation rates of organic matter are in accordance with the spatial patterns of primary production in the alboran sea higher in the western part due to the presence of the western alboran gyre however near bottom redistribution leads to the homogenisation of organic matter concentrations in bottom sediments of any given area finally from comparisons with sediment trap data the degradation of organic matter has been estimated to be approximately 30 40 of what reaches the bottom

evidence of a high productivity area off the coast of malaga from studies of diatoms in surface sediments abstract the assemblages of diatoms contained in nineteen surface sediment samples recovered off the coast of malaga province spain between 5 w and 4 38 w have been analysed the variations observed in the diatom assemblage point to the presence of nutrient enriched waters transported laterally from the centre of an upwelling that occurs to the west of the study area the utility of species such as paralia sulcata thalassionema nitzschioides and the spores of chaetoceros spp in the reconstruction of physico chemical and biological characteristics and of the spatial structure of the upwelling is confirmed

late pliocene climate in the southeast atlantic preliminary results from a multi disciplinary study of dsdp site 532 abstract site 532 on the walvis ridge was sampled at 4000 to 800 year intervals from 2 24 to 2 60 ma spanning the three large glacial advances of the late pliocene an age model was created by correlating the oxygen isotope record to site 607 with linear interpolations between tie lines the resultant age model differs from that in the site reports by more than 800 000 years due to misidentification of a magnetic boundary sedimentation rates varied by an order of magnitude at this site with minimum accumulation during glacial events interglacial intervals were charactrized by high marine production and high summer precipitation on land while glacials had very low production and arid continental climate during the large glacial events stages 96 100 conditions of low production and continental aridity reached their greatest intensity but there is no evidence of a permanent mode shift in either marine or terrestrial records calcite concentration has a strong variation at obliquity frequencies with maxima during interglacials but occasionally shows a large amplitude at precessional frequencies as well so that high concentrations occur in a few glacial intervals as a result color variation is not a reliable guide to glacial scale cycles at this site composition of the phytoplankton assemblage is diverse and highly variable and we have not been able to distinguish a clear indicator of upwelling related production spectral analysis reveals obliquity and precessional signals in the pollen data while several diatom records contain combination tones indicating that these data represent a complicated response to both local and high latitude forcing

evaporite evidence of a mid holocene c 4550 4400 cal yr bp aridity crisis in southwestern europe and palaeoenvironmental consequences sedimentological evidence for an abrupt dry spell in south eastern spain during the middle holocene from c 4906 to 4384 cal yr bp is presented this phase was determined primarily from halite beds deposited between muddy slimes in a lagoon system of puerto de mazarron murcia province with a peak phase from c 4550 to 4400 cal yr bp a multi core multi proxy study of 20 geotechnical drills was made in the lagoon basin to identify the main sedimentary episodes and depositional environments the results suggest that this halite bed more than 80 cm thick was conditioned by climate change and was accompanied by a generalized drying out of the basin halite precipitation was linked with palaeoecological changes including forest and mesophyte depletions and increasing cover and diversity of xerophytic plant species archaeological evidence indicates a demise of the population at this period probably due to resource exhaustion an overall picture of the biostratigraphy and palaeoclimates of the region is given in a broader geographical context

palaeoceanography of the last deglaciation in the alboran sea western mediterranean stable isotopes and planktonic foraminiferal records abstract oxygen isotope changes of the foraminiferal species globigerina bulloides and uvigerina peregrina eleven radiocarbon dates on the sediment fraction above 50 m and 13 biostratigraphical events allow us to correlate and to date the sediment record of the last climatic cycle in four cores from the alboran sea nine ecozones are recognized which differ from those previously established for atlantic sediments cored immediately west of gibraltar these ecozones can be grouped into two broad phases from the last glacial maximum up to near 9 500 yr b p cold north atlantic microfaunas are the major component of the assemblages during this interval dominant species replace each other according to the varying temperature and density stratification of the water masses from 9 500 yr b p up to the present time subtropical forms from the central atlantic dominate the northern atlantic forms an abrupt increase in the percentages of g inflata occurred near 7 000 b p this event was diachronous within the mediterranean during the last glacial g inflata was endemic inside the mediterranean and its abrupt increase near the end of the deglaciation did not result from replenishment from the atlantic between 4 000 and 5 000 yr b p percentages of g bulloides also increased abruptly warming conditions associated with the onset of a seasonal thermal stratification and a contrasting winter vertical convection are strongly suggested

microplankton response to environmental conditions in the alboran sea western mediterranean one year sediment trap record abstract the present work analyses the seasonal evolution of planktonic assemblages and particle fluxes through the water column in the eastern alboran sea western mediterranean at 35o55 47 n 01o30 77 w a sediment trap was deployed below the influence of the almeria oran front aof a semi permanent geostrophic front during july 1997 to june 1998 overall the temporal variability of coccolithophore planktonic foraminifer diatom benthic and wind carried biogenic particle fluxes is linked to the seasonal evolution of sea surface hydrological structures maximum planktonic fluxes were found during high productivity periods and wind induced upwelling following a trimodal pattern with maximum fluxes in july 1997 november december 1997 and april may 1998 these periods were characterized by vertical mixing and the full development of anticyclonic gyres in the alboran sea the annual flux of coccolithophores was dominated by the small gephyrocapsa group and emiliania huxleyi whereas turborotalita quinqueloba and globigerina bulloides dominated the foraminiferal fluxes and chaetoceros resting spores rs were predominant in the diatom assemblage benthic specimens were also collected with the sediment trap suggesting a variable influence of bottom water activity wind driven particles phytoliths and fresh water diatoms were collected along the year but their fluxes followed the local wind regime the high sea surface temperature sst during fall due to weaker than usual westerly winds and the pressure anomaly prevailing in the alboran sea during early winter were reflected in the planktonic assemblages by the proliferation of warm lower photic layer inhabitants and or oligotrophic taxa of coccolithophores florisphaera profunda planktonic foraminifers globigerinoides ruber and globorotalia inflata and diatoms leptocylindrus danicus these unusual climatic conditions in the eastern alboran sea must have been caused by the 1997 1998 enso event

seismic evidence for partial lithospheric delamination model of colorado plateau uplifts the lithospheric structure beneath the colorado plateau and great basin of the western united states is investigated using pn and surface wave data from the colorado plateau great basin broadband seismic experiment average pn velocities of 8 0 km s in the colorado plateau and 7 8 km s in the eastern great basin are found teleseismic rayleigh waves are also measured and eastern great basin phase velocities are found to be 3 4 higher than colorado plateau phase velocities in the 20 35 s range but indistinguishable at periods greater than 40 s the apparent pn surface wave discrepancy is resolved with models that include a thicker crust and faster mantle lid for the colorado plateau than the eastern great basin models for both regions require a mantle low velocity zone the slow mantle deep beneath the colorado plateau may suggest a thermal origin of plateau uplift which has not yet penetrated the mantle lid

sn velocities in western and eastern north america we have investigated the use of the new delay time data set of engdahl et al 1997 for the construction of tomographic images of sn velocity in north america the delays show a significant difference in average delay between paths located west and east of 105 w this difference is larger when paths longer than 10 are included indicating a positive gradient for the s velocity in eastern north america discarding outliers two separate regions in the western and eastern united states and canada where imaged low velocities were found under the colorado plateau extending westwards towards the gulf of california in the eastern u s the michigan basin stands out with low sn velocity and the grenville province is characterized by a positive anomaly

palaeoproductivity changes and upwelling variability in the galicia mud patch during the last 5000 years geochemical and microfloral evidence theholocenepalaeoclimatichistoryofthegaliciancontinentalshelfhasbeeninvestigatedthrough theanalysesofdiatomremains othersiliceouscompounds biogenicsilica bsi andmetalscontentinamul tiproxyapproachtoagravitycorerecoveredfromthegaliciamudpatch nwiberianpeninsula coveringthe last 5000 years downcore changes in diatom assemblages composition and abundance reflect changes in diatomproductionrelatedtolong short termvariationsinclimate regionaloceanography upwellingstrength and river influx off the coast of nw spain and portugal palaeoclimatic variability was related to the relative strengths and position of the azores high and iceland low pressure cells metals and microflora fluctuations are interpreted as changes in the riverine influence and upwelling intensity paced by oceanographic atmos pheric and climatic changes lack of diatoms between 4700 3300 and 1800 1200 cal yr bp could be linked to early diagenetic processes taking place in the sediment after burial biogenic barium baexcess metals and diatomassemblages showageneralincreaseofmarineproductivityforthelast1200cal yrbp between800 and500cal yrbphighproductionofthemicrofloraistriggeredbyinfluxofriver derivednutrientsundercon ditionsofswwindsandstormsresultingfromanaonegative likephase thebiosiliceousandgeochemical signatures of sediments from the last 500 cal yr bp indicate conditions of enhanced upwelling and increased

a 220 000 year climatic record for the east equatorial atlantic ocean and equatorial africa evidence from diatoms and opal phytoliths in the zaire congo deep sea fan accumulation rates of microfossil associations are independent of each other and in addition to percentages give indispensable information about the significance of micropaleontological data marine diatoms reveal that coastal upwelling in the zaire fan region was strong during glacial stages and weaker during interglacial stages oceanic upwelling was intense in stages 6 and 2 and at the stage 5d 5c transition but not in stage 4 the benguela current did not penetrate into the gulf of guinea during the last 220 000 years the phfd index based on the contribution of freshwater diatoms and phytoliths is a measure of aridity in equatorial africa the production in the low salinity river plume was high in the most humid periods on land and low when the continent was arid on the long term nutrient supply of the zaire river to the ocean was probably larger in humid than in arid periods periods of strong seasonal variability in river fluxes and coastal upwelling coincide with arid intervals except in the very humid interval with strong seasonal contrasts 35 000 20 000 years b p

variations of diatom flux in the eastern equatorial atlantic during the last 400 000 years meteor cores 13519 and 13521 abstract two cores from the eastern equatorial atlantic have been analysed for their diatom content to study the relationship between diatom abundances and paleoclimate in both cores fluctuations of the contents of freshwater diatoms and phytoliths reflect changes in aridity on the continent highest abundance of land derived material was found in the southernmost core indicating that the main supply was by southerly winds large abundances of freshwater diatoms mainly aulacosira melosira granulata coincide with periods of ice growth and increasing trade wind intensity provided a sufficient source area aridity the southerly core also contained a large number of marine diatoms including ethmodiscus rex oozes e rex seems to be an opportunist preferring the extremely high nutrient conditions provided by upwelling in periods of strengthened trade winds during glacials marine diatoms other than e rex occurred at periods of decreasing trade winds with reduced upwelling i e less extreme nutrient conditions than during the formation of e rex oozes

20 000 years of nile river dynamics and environmental changes in the nile catchment area as inferred from nile upper continental slope sediments multi proxy analysis of two marine sediment cores ms27pt and md04 2726 from the nile continental slope provides evidence of changes in nile sediment discharge related to changes in ethiopian african monsoon eam precipitation and allows us to reconstruct changes in nile river runoff vegetation and erosion in the nile headwaters sediment element composition and neodymium isotopic composition reveal significant changes in clastic sediment provenance with sources oscillating between a saharan aeolian contribution during the last glacial maximum deglacial transition and during the late holocene and a blue atbara nile fluvial contribution during the african humid period ahp this study provides a new understanding of past environmental changes between 14 6 and 14 13 ka there was a major input of sediments from the ethiopian highlands consistent with a stronger eam at that time climate in the nile basin was wetter between 14 8 and 8 4 ka with a corresponding increase in blue nile water and sediment discharge via the main nile into the eastern mediterranean the gradual climatic transition from the ahp to the present day dry climate was reflected in a decrease in blue nile sediment deposition and flood discharge between 8 4 and 3 7 ka with aridity at a maximum between 3 7 and 2 6 ka the onset of drier conditions in the blue nile basin seems to have begun before the 8 2 ka cooling event in the north atlantic we speculate that the climatic change from the wet ahp to the dry late holocene may have been a result of a break in the low latitude dynamic equilibrium between climate vegetation and erosion which may in turn have affected the climate in higher latitudes reduced nile flow may also have had an impact on levantine intermediate water originating in the eastern mediterranean through an increase in intermediate water formation

ocean surface and wind dynamics in the atlantic ocean off northwest africa during the last 140 000 years abstract a combined micropaleontological analysis of core camel 1 from the oligotrophic sierra leone rise area has allowed reconstruction of the paleoclimatic and paleoceanographic history of the region for the last 140 kyr the ratio n between the reticulofenestrids coccolithophore indicators of relatively high nutrient contents versus florisphaera profunda a lower photic zone coccolithophore allowed us to monitor changes in the nutricline depth these results were compared with those obtained for marine diatom and planktic foraminifera assemblages thus a shallow nutricline thermocline and high productivity during stages 6 5d 5b 4 and 2 is proposed this situation can be correlated with maximum input of biosiliceous wind transported particles fresh water diatoms and phytoliths in sea sediments the shallow nutricline is correlated with an intensification in atlantic divergence and or a north equatorial current intensification when the ne trades were enhanced for glacial and stadials cold periods a clear precessional component is observed in the surface water dynamics during the last climatic cycle minima in the n ratio coinciding with minimum insolation during winter in the boreal hemisphere during mis 5 4 and 2 dry conditions were dominant on the northern african continent corresponding to a more intense ne trade wind circulation the increased phytolith concentrations during mis 6 are consistent with a more intense seasonality on the african continent cold planktic foraminifera assemblages show an eccentricity component linked to northern ice sheet dynamics this situation is enhanced in isotope stages 6 and 3 due to an intensification in the north equatorial current the eccentricity component is also observed both in the n ratio coccolithophore related and in the total planktic foraminifera

history of the last deglaciation in the alboran sea western mediterranean and adjacent north atlantic as revealed by coccolith floras abstract a series of cores recovered from the alboran sea western mediterranean and the adjacent part of the north atlantic has revealed very high rates of accumulation which have enabled us to identify the stages of the last deglaciation in great detail isotopic analyses of the cores show the two steps of the deglaciation terminations 1a and 1b separated by the bolling allerod warm phase 14 c dating of the cores has allowed the dating og the climatic succession we have identified each event of the deglaciation on the basis of changes in the coccolith flora especially in species of the genus gephyrocapsa such changes reflect surface water changes since coccolith live only in the photic zone the abundance of g muellerae in the cold intervals prior to each termination is greater than that in the bolling allerod and holocene warm intervals which follow the terminations coversely g oceanica is virtually absent during cold intervals but becoms more common during the warmer periods during the first deglacial warming there is a large influx of fine grained detrital material presumably derived from increased run off from the nearby mountains of southern spain and north west africa in the alboran sea cores with the most expanded sections there is a marked increase in the percentage of syracosphaera histrica at the beginning of this increase of detritus no increase was found in the atlantic core at this time

mapping high pn velocity beneath the colorado plateau constrains uplift models the massive international seismological centre data set of the past 20 years and the two station method are used to determine pn velocities in the mantle lid beneath the colorado plateau in this method the event is located at distances where pn is the first arrival 2 16 and the path is in or very near the azimuth of the two station pair and crosses the plateau this technique to a large extent minimizes the hypocenter mislocation effect and possible errors due to variations in the crustal structure near the source since only the difference in travel times at the two stations is used however this technique has a few underlying assumptions and possible sources of errors such as the quality of the pn data base and station delays caused by varying crustal structure that require an extremely careful application of the method a detailed study of the source of errors and a methodology of selection of the data are presented application of this method to the colorado plateau using all possible two station pairs from 53 stations located within or along the margin of the plateau yields an average high pn velocity of 8 12 0 09 km s this value is considerably larger than the average value of 7 83 km s based on available but very limited seismic refraction profiles but is remarkably similar to the average value of 8 1 km s for the relatively stable midcontinent region our new pn velocity for the colorado plateau eliminates the paradox in the literature that emphasizes the rather close similarity between average pn velocities beneath the colorado plateau and the basin and range province while their tectonic and magmatic cenozoic history is dramatically different previous models for the structure and evolution of the plateau have used the low pn velocity as an important constraint on density and thermal state of the lithosphere hence such models should be reexamined on the basis of this new uppermost mantle pn velocity determination there are two main models that have been proposed to explain the 2 km uplift of the colorado plateau one is based on a combination of thermal thinning of the lithosphere and crustal thickening and the other involves a combination of the delamination of the subducted subhorizontal farallon oceanic plate from the overriding north american plate and crustal thickening we show that the delamination model is more readily consistent not only with our velocity determination and the elevation of the plateau but also with varied geological observations reported in the literature that concern the cenozoic evolution of western north america

contrasting lithospheric structure between the colorado plateau and great basin initial results from colorado plateau great basin passcal experiment the colorado plateau great basin cpgb passcal experiment provides broadband seismic data that allow us to determine crustal and upper mantle structure in the colorado plateau and eastern great basin twelve portable broadband seismometers throughout utah and nevada are supplemented by permanent broadband stations in the region receiver functions indicate an average crustal thickness of 35 5 km in the great basin gb with a strong p to s ps conversion from the moho the crust in the transition between the great basin and colorado plateau cp produces a strong intracrustal conversion the cp has somewhat thicker crust 42 5 km and weaker moho conversion br surface wave phase velocities are 3 4 higher than cp phase velocities in the 20 35 s range consistent with a thinner crust under the gb the phase velocities at periods greater than 40 s are indistinguishable between the two provinces indicating that differences between upper mantle velocities are minor shear wave splitting yields fast polarizations that parallel the western and northern boundaries of the cp with delay times decreasing towards the center of the plateau

contemporary seismicity faulting and the state of stress in the colorado plateau the contemporary seismicity of the colorado plateau based on seismic monitoring in the past 30 yr can be characterized as being of small to moderate magnitude and contrary to earlier views of a low to moderate rate of occurrence with earthquakes widely distributed concentrations of earthquakes have been observed in a few areas of the plateau the most seismically active area of the colorado plateau is the eastern wasatch plateau book cliffs where abundant small magnitude seismicity is induced by coal mining the largest earthquakes observed to date of estimated richter magnitude m l 5 6 have generally occurred in northern arizona although very few earthquakes can be associated with known geologic structures or tectonic features in the colorado plateau seismicity appears to be the result of the reactivation of pre existing faults lacking surficial expression but favorably oriented to the tectonic stress field the small to moderate size of the earthquakes and their widespread distribution are consistent with a highly faulted precambrian basement and upper crust and a moderate level of differential tectonic stress earthquakes in the plateau generally occur in the upper crust from the near surface to a depth of 15 20 km although events have been observed in both the lower crust and uppermost mantle in areas of low to normal heat flow the latter suggests that temperatures are sufficiently low at these depths that brittle failure and hence earthquakes are still possible the predominant mode of tectonic deformation within the plateau appears to be normal faulting on northwest to north northwest striking faults with some localized occurrences of strike slip faulting on north west or northeast striking planes at shallow depths the contemporary state of stress within the plateau is characterized by approximate northeast trending extension in contrast to the previous belief that the plateau was being subjected to east west tectonic compression one area of the plateau the eastern wasatch plateau and book cliffs may still be characterized by compressive stresses however the nature of these stresses is not well understood

crustal structure of the northwestern basin and range province from the 1986 program for array seismic studies of the continental lithosphere seismic experiment the basin and range province of the western united states is characterized by active east west extension at strain rates of 1 cm yr 1 high regional heat flow of 90 mw m 2 and widespread late cenozoic bimodal rhyolitic basaltic magmatism the 1986 program for array seismic studies of the continental lithosphere basin and range seismic experiment imaged a portion of northwestern nevada to determine the crustal structure and to assess reported differences between refraction versus reflection determinations of moho depth and how the crustal composition and structure has been influenced by volcanic and extension mechanisms our interpretation of the refraction wide angle reflection data suggests that the crust is fairly uniform in thickness and varies by less than 5 km over the 280 km east west profile and 3 km over its 220 km north south length we characterize the velocity structure by five layers 1 an upper most crust composed of sedimentary rocks and basement that has an average velocity of 5 7 km s i 2 a middle crust that extends to a depth of 18 22 with an average velocity of 6 1 km s 1 3 a 10 12 km thick lower crust with an average velocity of 6 6 km s 1 4 a 2 5 km thick transitional crust mantle boundary defined by a 7 6 km s l velocity and 5 an upper mantle with an average pn velocity of 7 9 8 0 km s 1 these data show a uniformily thick crust of 28 km 5 km beneath northwestern nevada and a lack of evidence for significant low velocity crustal layers in general the entire crustal column exhibits uniform positive velocity gradients of 0 02 0 04 s the midcrustal discontinuity is interpreted as a small velocity increase of 0 2 km s l at 18 km depth the absence of a significant midcrustal reflection and the presence of large velocity gradients throughout the crust arises either from 1 a systematic increase in mafic composition with depth or 2 possibly high lower crustal pore pressure that acts to decrease the velocity contrast across the midcrustal boundary our interpreted seismic velocity structure is consistent with a broad range of bulk compositions for the crust upper crustal velocities are consistent with bulk compositions that range from metasediments and granites at shallow depth to diorites at midcrustal levels while lower crustal velocities suggest bulk compositions that range from diorites and amphibolities at midcrustal depths to mafic granulites and gabbros at the base of the crust the uniform crustal thickness of 30 34 km in northwestern nevada is close to the crustal average for the basin and range province but is thin when compared to surrounding regions such as the sierra nevada and colorado plateau where crustal thickness is greater than 40 kin similarily northwestern nevada pn velocities of 7 9 8 0 km s 1 are near the province wide average of 7 9 km s l temperature corrected pn velocities from a 90 mw m 2 geotherm for the basin and range to 60 mw m 2 for the stable interior of the united states are within one standard deviation of the continental average of 8 05 km s i and suggest a uniform upper mantle composition across the basin and range in addition to these observations the homogeneity of the velocity structure beneath the western basin and range argues for a youthful moho and crust that has been reworked by province wide late cenozoic extension episodic magmatism and underplating

molecular stratigraphy a new tool for climatic assessment variations in sea surface temperatures over the past 500 000 years are inferred from the relative abundance behaviour of two organic compounds c37 alkenones over the upper 8 metres of a sediment core from the eastern equatorial atlantic this molecular record ascribed to contributions from prymnesiophyte algae correlates well with the variations in the 18 signal for the calcareous skeletons of certain planktonic foraminifera thus providing the first demonstration of a new stratigraphical technique which may be especially valuable where methods based on carbonate 18 fail

variations in the structure of the anticyclonic gyres found in the alboran sea historical satellite aircraft and in situ data have shown that two anticyclonic gyres the western and eastern alboran gyres are major ocean features of the alboran sea an examination of several years of satellite imagery indicates that large variations in the surface expression of these two gyres occur and that on occasion one or the other gyre disappears the disappearance of both gyres at the same time was not seen the initial disappearance of either gyre occurs on a time scale of a week to 2 weeks whereas the return may take from 3 weeks to 2 months various forcing mechanisms i e winds mass flux inflow through the straits of gibraltar and sicily and or density have been used in numerical ocean circulation models to study the dynamics of the western mediterranean sea various model results show relationships similar to those shown by the satellite imagery however no single forcing mechanism has been positively identified as the source of the disappearances and the events may be a result of a combination of forcing mechanisms

links between marine and atmospheric processes oscillating on a millennial time scale a multi proxy study of the last 50 000 yr from the alboran sea western mediterranean sea abstract the large dataset obtained from the extensive study of images core md95 2043 recovered from the alboran sea western mediterranean shows the periodicities and phase relationships of oceanographic and atmospheric processes on a millennial time scale the 1470 yr cycle is the most significant with the exception of the records reflecting climatic or environmental changes on land which show statistically significant 3300 and 8000 frequency bands the investigation of these core records on a millennial scale resolution allows us to establish the evolution of oceanographic and atmospheric mechanisms that influenced the western mediterranean region in the course of the dansgaard oeschger cycles accordingly possible land sea interactions can be identified and situated in the context of the temporal succession of the different climatic processes for instance saharan dust supply from northern africa appears to lead high latitude climate changes suggesting that low latitude feedback processes were involved in forcing the millennial climatic variability in the westernmost mediterranean

a study of an intense density front in the eastern alboran sea the almeria oran front abstract studies of satellite imagery and space shuttle photographs of the western mediterranean have indicated that the main path of inflowing atlantic water is around two large anticyclonic gyres in the alboran sea and along the algerian coast these studies have also shown that a strong ocean front is present between almeria spain and oran algeria which is part of the easternmost segment of the eastern alboran gyre based on these satellite studies the first in situ investigation of the front called here the almeria oran front was conducted in march 1986 as part of the winter campaign of the western mediterranean circulation experiment wmce analyses of the resulting data show that the almeria oran front is a large scale density front formed by the convergence of two distinct water masses and controlled by the geographic position and strength of the eastern alboran gyre physical and biochemical data indicate that the front is limited to the upper 300 m with a strong southward baroclinic jet

cold water coral mounds in the southern alboran sea western mediterranean sea internal waves as an important driver for mound formation since the last deglaciation abstract cold water corals cwcs are widely distributed in the entire alboran sea western mediterranean sea but only along the moroccan margin they have formed numerous coral mounds which are constrained to the west and the east melilla cwc mound provinces wmcp and emcp while information already exists about the most recent development of the coral mounds in the emcp the temporal evolution of the mounds in the wmcp was unknown up to the present in this study we present for the first time cwc ages obtained from four sediment cores collected from different mounds of the wmcp which allowed to decipher their development since the last deglaciation our results revealed two pronounced periods of coral mound formation the average mound aggradation rates were of 75 176 cm kyr 1 during the bolling allerod interstadial and the early holocene only temporarily interrupted during the younger dryas when aggradation rates decreased to

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

diatom record of late quaternary climatic change in the eastern equatorial atlantic and tropical africa over the last 160 000 years diatom productivity in the equatorial atlantic has been high during glacial stages 2 4 and 6 and moderate during parts of substages 5b and 5d approximately 96 000 and 117 000 years b p productivity of diatoms is particularly low in substage 5e and in the middle of stage 1 higher productivity implies more vigorous trade winds during glacial intervals leading to stronger upwelling and enhanced lateral advection of surface waters the influence of the benguela current near the equator was strongest during stage 2 a separate regime of coastal upwelling may have existed in the gulf of guinea at this time upwelling and advection may not always respond to the same forcing as sea surface temperature results support the hypothesis that ethmodiscus rex oozes result from high diatom productivity runoff from the zaire and niger rivers was highest at the stage 2 1 transition and just prior to the stage 6 5 transition due to intensification of the african monsoon several other times of increased runoff are indicated periods of increased surface water circulation in the eastern equatorial atlantic appear to correspond to times of aridity in tropical africa conversely intervals of decreased circulation in the eastern equatorial atlantic coincide with times of humidity in tropical africa precessional forcing of continental climate is suggested however precessional forcing of surface ocean circulation can be neither confirmed nor refuted based on the records examined here influx of antarctic bottom water to the eastern equatorial atlantic has been insignificant throughout the last 160 000 years

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