oxygen isotope analyses and pleistocene ice volumes abstract the oxygen isotope record from fossil foraminifera in deep sea sediments is commonly used as a proxy for global ice volume the linkage between 18 o and ice volume however is probably nonlinear we have developed a simple numerical model of the isotopic response of the oceans to ice volume change the major features it simulates are 1 the changing mean isotopic composition of snow as a function of ice volume colder snow temperatures forced by climate change and higher elevation accumulation areas imply more negative mean 18 o 2 the nonequilibrium isotopic composition of ice sheets the past history of an ice sheet is integrated into its mean isotopic composition which introduces a lag of isotopic ice volume i e the measured 18 o record scaled to ice volume units behind true ice volume 3 selective preservation of isotopically more negative colder higher latitude ice this geographic effect can selectively amplify or dampen the isotopic response to the ice volume signal we illustrate the response of our model to simple hypothetical ice volume transitions of ice growth and ice decay sensitivity tests are illustrated for all model parameters the results suggest that oxygen isotope records reproduce the general patterns of ice volume change fairly accurately the foraminiferal isotope record however may misrepresent the true amplitude of the ice volume signal and lag true ice volume by 1000 to 3000 yr

modeling phosphorus cycling and carbon burial during cretaceous oceanic anoxic events article i nfo in the greenhouse world of the cretaceous there were episodes of oxygen depletion in the deep ocean associated with enhanced organic carbon burial in sediments black shale formation in this study we use a box model of the oceanic phosphorus p organic carbon orgc and oxygen cycles to explore the hypothesis that variations in marine p availability control deep ocean oxygen depletion anoxia and the formation of black shales under cretaceous ocean conditions we find that for the cretaceous ocean with large continental shelves slow oceanic overturning and high sea surface temperatures oceanic anoxic events oaes can be triggered by enhanced p supply from land and that the system is particularly sensitive to oceanic mixing in our baseline scenario the deep sea becomes completely anoxic while the shelves attain only partial anoxia sedimentary burial differs between the shelves and open ocean while organic carbon burial is enhanced in both regions deep sea reactive p burial decreases dramatically under anoxia but not on the shelves where oxygen depletion is not complete furthermore our model results imply that oaes can be sustained by p recycling from sediments under low oxygen conditions ultimately however the feedbacks which result in the accumulation of atmospheric oxygen terminate the anoxic event atmospheric oxygen is modulated by land processes such as forest fires and oxidative weathering which limit the rise of atmospheric o2 our model findings are corroborated by p burial data from the geological record for oae2 approximately 94 myr bp through a sensitivity analysis we identify two necessary criteria for oaes low mixing of surface and deep waters poor ocean ventilation and enhanced sedimentary p recycling under low oxygen conditions when these criteria are met ocean anoxia is a robust result to a mild increase of continental supply of phosphorus under a wide range of environmental conditions

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

calcareous nannofossil biostratigraphy of the m del casino section northern apennines italy and paleoceanographic conditions at times of late miocene sapropel formation a detailed quantitative calcareous nannofossil analysis has been performed on 138 samples from the astronomically dated monte del casino section with the aim to identify and precisely date the most important calcareous nannofossil events across the tortonian messinian boundary in the mediterranean and to unravel paleoceanographic conditions at times of sapropel formation during the late miocene from the biostratigraphic perspective the genus amaurolithus provides three successive first occurrences fos a primus a c f amplificusand a delicatus dated at 7 446 7 434 and 7 226 ma respectively other bioevents include the base and top of the small reticulofenestrids acme dated at 7 644 and 6 697 ma and the fo fco and lo of r rotaria dated at 7 405 7 226 and 6 771 ma these events appear to be useful in improving biostratigraphic resolution in the tortonian messinian boundary interval at least for the mediterranean quantitative analysis revealed changes in the calcareous nannofossil assemblage associated with the sapropels the observed fluctuations suggest a single mechanism for sapropel formation in the mediterranean during the late neogene sapropels are characterized by a decrease in the total number of coccoliths interpreted mainly as a reduction in calcareous nannofossil production due to increased siliceous plankton production during spring blooms and an increase in reworked specimens interpreted to reflect enhanced continental input via river run off an increase in abundance of the genus rhabdosphaeracan be explained by opportunistic behavior at the end of the spring bloom when nutrient levels start to become impoverished as far as sea surface water temperature indicators are concerned warm water d pentaradiatus shows positive fluctuations in sapropels while cooler water d intercalaris and c pelagicus show negative fluctuations 1999 elsevier science b v all rights reserved

stable isotope anomalies in mediterranean pleistocene records oxygen and carbon isotope records of twelve mediterranean cores raised from west alboran sea to east off israel and of four atlantic cores raised from the western side of gibraltar and located respectively inside below and beyond the modern mediterranean outflow are compared to open ocean records of core 71 139c from the north atlantic and core v19 30 from the east pacific oxygen isotope stratigraphies can be established for deep mediterranean records and the major events of the last 150 ka are easily identifiable for instance the five substages of stage 5 or the 18 ka event stage 2 are identified but the 10 ka event younger dryas is only recorded by globigerina bulloides and benthic foraminifera suggesting that the cooling affected only winter sst 14c dates for the two terminations ia and ib of the last deglaciation which are recorded in sediment cores from areas with high sedimentation rates faro ridge alboran sea sicilian strait are in good agreement with the dates published for the same termination in atlantic cores an intermediate step however has been identified in some cores at 14 ka and divides termination ia into two phases oxygen isotope anomalies are recorded by the shallow water species globigerinoides ruber they correspond to 1 a higher amplitude glacial interglacial change in 18o values which exceeds that of the open ocean by 1 in the western basin and by 1 7 in the eastern basin 2 large isotopic depletions during the deposition of sapropel s1 s3 and s5 they are interpreted as the result of fresh water run off responsible for a strong dilution in the shallower layers of the east mediterranean waters the isotopic effect of this dilution averages 0 75 for sapropel s1 and 1 6 for sapropel s5 during the last glacial maximum the mediterranean still acted as a concentration basin and a gradient of 18o values similar to the modern one 0 75 existed from west to east in the deep waters apparently deep water temperatures were lower during the last glacial but the decrease did not exceed 4 c in the eastern basin major anomalies are also contained in the 13c records of g bulloides and benthic foraminifera the 13c records from surface intermediate and deep waters of the eastern basin and from intermediate and deep waters of the western basin are opposite to that of the open ocean during glacial time 13c values were higher in intermediate and deep waters of the whole mediterranean and also in surface water of the eastern basin at the same time the 13c gradient of surface to deep waters was low this gradient increased during the last deglaciation while 13c values of g bulloides and benthic foraminifera decreased this decrease interrupted at 10 ka may have been related to increased fresh water run off from the bordering contintents due to increased precipitation especially in the tropical belt the 13c depletion is clearly recorded in the levantine and deep water masses and can be traced westward in the mediterranean outflow oxygen and carbon isotope anomalies recorded simultaneously in the east mediterranean by the shallow water species globigerinoides ruber during sapropel deposition indicate that increased precipitation on the bordering continents and strong fresh water run off during the time of the last deglaciation may have caused a density stratification and deep stagnation in the eastern basin uncertainties arise from the fact that in the mixing model deglacial mediterranean waters are mixed with continental fresh waters the isotopic characteristics of which are not entirely understood although increased surface water production of biogenic material can not be excluded as a possible cause of 13c depletion it appears that the river discharge including the nile as well as black sea input are also plausible sources for the fresh water layering

deglacial warming of the northeastern atlantic ocean correlation with the paleoclimatic evolution of the european continent abstract isotopic micropaleontologic and pollen analyses of deep sea cores from the bay of biscay and the northeastern atlantic ocean show that the deglacial warming of this oceanic area was closely correlated with the paleoclimatic evolution of the adjacent european continent temperatures were at least as warm as those of today in the bay of biscay between 13 300 and 11 000 b p coinciding with the combined bolling allerod warm continental events a major spread of polar water occurred between 11 000 and 10 000 b p during this event which coincides with the younger dryas continental cold event marine temperatures were almost as low as those of the last glacial maximum the final deglacial warming of the norteastern atlatntic ocean occurred during the following 3000 yr

reconstructing past planktic foraminiferal habitats using stable isotope data a case history for mediterranean sapropel s5 abstract a high resolution stable o and c isotope study is undertaken on all planktic foraminiferal species that are reasonably continuous through an eemian sapropel s5 from the western side of the eastern mediterranean the data are considered within a context of high resolution isotope records for two further s5 sapropels from the central and easternmost sectors of the basin alkenone based sea surface temperature records for all three sapropels and planktic foraminiferal abundance records for the same sample sets through all three sapropels results are compared with similar data for holocene sapropel s1 the adopted approach allows distinction between species that are most suitable to assess overall changes in the climatic hydrographic state of the basin including depth related differentiations and the main seasonal developments and species that are most affected by variable biological controls or local regional and transient physico chemical forcings it is found that a priori assumptions about certain species palaeohabitats based on modern habitat observations may become biased when non analogue conditions develop in the case of mediterranean sapropel s5 these consisted of enhanced freshwater dilution elevated productivity shoaling of the pycnocline between intermediate and surface waters and stagnation of the subsurface circulation under these conditions some species are found to shift into habitat settings that differ considerably from those occupied today the present multiple species approach can identify such anomalous responses and thus offers a sound background for further shell chemistry investigations and quantitative interpretation of the isotopic profiles we capitalise on the latter potential and offer the first quantitative estimates of monsoon flooding into the mediterranean during the deposition of eemian sapropel s5

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

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

putting the younger dryas cold event into context abstract the younger dryas event is by far the best studied of the millennial scale cold snaps of glacial time yet its origin remains a subject of debate the long held scenario that the younger dryas was a one time outlier triggered by a flood of water stored in proglacial lake agassiz has fallen from favor due to lack of a clear geomorphic signature at the correct time and place on the landscape the recent suggestion that the younger dryas was triggered by the impact of a comet has not gained traction instead evidence from chinese stalagmites suggests that rather than being a freak occurrence the younger dryas is an integral part of the deglacial sequence of events that produced the last termination on a global scale

nile water as a cause of eastern mediterranean sapropel formation evidence for and against during the late pleistocene sapropels layers of organic carbon rich sediment formed throughout the entire eastern mediterranean basin in close association with glacial interglacial transitions the current theory for the mechanism of sapropel formation involves a density stratification of the water column due to the invasion of a large quantity of low saline water which resulted in oxygen depletion of the bottom waters most workers believe that this low salinity water was glacial meltwater that entered the mediterranean via the black sea and a series of interconnected glacial lakes but the suggestion also has been made that the freshwater originated from the nile river in this study the oxygen isotope values of planktonic foraminifera globigerinoides ruber have been examined in six gravity cores and one piston core from the southern levantine basin and compared with the oxygen isotope records ofg ruber from other areas of the eastern mediterranean this study deals mainly with the latest sapropel which was deposited approximately 7000 to 9000 years ago results indicate that nile discharge probably does reduce salinities somewhat in the immediate area surrounding the mouth of the nile but this water is rapidly mixed with the highly saline waters of the easternmost mediterranean using a mixing equation and surface water salinity limitations an approximate oxygen isotope balance of surface waters was calculated for the time of latest sapropel deposition this calculation shows that neither nile river discharge nor black sea input nor both together are large enough to account for the large scale oxygen isotope depletion associated with latest sapropel deposition in the eastern mediterranean this suggests that part of the isotopic change at termination i is probably due to increased surface water salinities during the last glacial maximum in addition evidence from the timing of sapropel 1 deposition and the dissolved oxygen balance indicates that deposition of the latest sapropel is associated with increased surface water production of biogenic material as much as three times higher than that of present day

carbon and oxygen isotope composition of foraminifera in two cores from the bannock basin area eastern mediterranean abstract two cores from the bannock basin in the eastern mediterranean have been analysed for 18 0 and the 13 c in planktonic foraminifera one core 02 pc was extracted from the anoxic brine the other 08 gc from a plateau east of the brine the absence of sapropelic muds in core 08 gc from the two holsteinian euxinic cycles together with the presence of isotopic spikes suggests that the plateau has risen during the last ca 200 000 years by ca 2 5 mm yr the 18 0 amplitude of globigerinoides ruber in eastern mediterranean cores is only ca 0 5 larger than for this species in north atlantic cores this suggests that the surface oxygen isotopic composition of both bodies of water followed each other fairly closely during the late pleistocene except during the stagnant phases

geochemical evidence for enhanced productivity during s1 sapropel deposition in the eastern mediterranean the geochemistry of the youngest mediterranean sapropel layer suggests changes in productivity and water column oxygen conditions during sapropel deposition the ba enriched interval is broader than the organic carbon rich interval of this sapropel we suggest that the ba enriched horizon records the original thickness of the sapropel prior to subsequent partial oxidation the main carrier of ba is barite as microcrystals 0 5 5 m having a morphology characteristic of marine barite particularly abundant beneath high productivity regions ba concentrations do not change at the sapropel layer oxidation front and diagenetic barite crystals are absent thus the ba enriched layer reflects original oceanic conditions of increased biological productivity during sapropel deposition and not diagenetic ba remobilization paleoredox indicators point to restricted oxygenated bottom water but not to fully anoxic conditions detrital elements within this layer indicate a lower eolian terrigenous input enhanced humidity and increased precipitation runoff thus likely higher nutrient supply supporting table is available on diskette or via anonymous ftp from kosmos agu org directory apend username anonymous password guest diskette may be ordered by mail from agu 2000 florida ave n w washington dc 20009 or by phone at 800 966 2481 15 00 payment must accompany order

tethyan cenomanian pelagic rhythmic sedimentation and pleistocene mediterranean sapropels is the biotic signal comparable a comparison between the biotic signal recorded in the tethyan cenomanian black shales and in the mediterranean pleistocene sapropels is proposed here to this end the antruiles section northeastern dolomites italy has been investigated as a reference section for the cenomanian black shales the data obtained based on calcareous nannofossils and foraminifera have been compared to those from a core in the mediterranean sea containing a complete succession of late pleistocene holocene sapropels our study suggests that deposition of black shales like sapropels occurred when the water column was stratified as implied by increased abundance of the cenomanian deeper dwellers rotalipora cushmani and r greenhornensis the superficial subsuperficial opportunist form heterohelix reussi which strongly increases in numbers within the black shales could be analogous to the modern surface dweller globigerinoides ruber which is abundant in late pleistocene holocene mediterranean sapropels the peaks of g ruber can be related to decreased salinity in surface water thus the increase of h reussi could also be related to a freshwater superficial layer we hypothesise also that an increase in abundance of watznaueria barnesae reflects conditions of superficial low salinity in black shales increases in abundance of dicarinella algeriana and praeglobotruncana gibba by analogy to modern neogloboquadrina dutertrei could reflect availability of food restricted to subsuperficial waters however a cretaceus equivalent of the pleistocene nannoplankton form florisphaera profunda which proliferates within the deep chlorophyll maximum is not observed in addition the abundance of h reussi indicates a well expanded oxygen minimum zone although less in extent than in pleistocene sapropels as shown by the occurrence within the cenomanian black shales of a benthic fauna even though reduced in size and impoverished spectral analysis applied to calcareous nannofossils identifies close relations with the milankovitch precession and eccentricity cycles in both the black shales and the sapropels

environmental and climatic changes in the jura mountains eastern france during the lateglacial holocene transition a multi proxy record from lake lautrey this paper presents a multi proxy reconstruction of the climatic and environmental changes during the last glacial interglacial transition as recorded by a sediment sequence from lake lautrey jura eastern france this reconstruction is based on analysis of pollen chironomid organic matter oxygen isotope mineralogical magnetic susceptibility and inferred lake level data at a high temporal resolution the chronology is derived using ams radiocarbon dates the position of the laacher see tephra lst and of correlation between the lautrey and grip oxygen isotope records this data set reveals a detailed sequence of environmental changes in the jura mountains from greenland stadial 2a to the early holocene biotic and abiotic indicators allow the recognition of major abrupt changes associated with the gs 2a gi 1e gi 1a gs 1 and gs 1 preboreal transitions and other minor fluctuations related to the cold events gi 1d gi 1b and the preboreal oscillation pbo they also suggest additional cooling spells at ca 14 550 and 14 350 cal yr bp intra bolling cold periods at ca 13 500 and ca 12 700 cal yr bp just before the gs 1 onset and at ca 11 350 cal yr bp just before the pbo as well as an intriguing brief warming episode within gs 1 at ca 12 080 cal yr bp summer temperature increased by ca 5 c at the start of gi 1e and by 1 5 3 c at the holocene onset while it decreased by ca 3 4 c at the beginning of gs 1 major changes in local hydrology and in seasonality appear to be also associated with the gs 2a gi 1e gi 1a gs 1 and gs 1 preboreal transitions pollen and abiotic indicators suggest a greater sensitivity of the vegetation cover to climatic oscillations during the first part of the lateglacial interstadial than during the second part after ca 13 700 cal yr bp when a closed forest had been restored in this area by contrast the restoration of forest cover took less than 300 yr after the end of gs 1 at the beginning of gi 1e and gs 1 no lag occurs within the sampling resolution of 20 50 yr in the responses of aquatic chironomids and terrestrial pollen ecosystems while at the onset of the holocene the response of the vegetation appears slightly delayed in comparison with that of the chironomid community finally the recognition of two successive tephra layers which were deposited just before the lst at ca 12 950 cal yr bp and which originated from le puy de la nugere massif central france provides an additional tephrochronological tool for correlation between lateglacial european sequences

barium in sediments off northwest africa a tracer for paleoproductivity or meltwater events 1 high resolution down core analyses of the solid phase content of total barium batot and total organic carbon toc back to 25 kyr b p were performed on a gravity core from the upper continental slope off cape yubi morocco the observed discrepancy between the two potential paleoproductivity proxies batot and toc initiated supplementary examinations of the pore water the geochemistry of the clay fraction x ray diffraction analyses and the application of a sequential ba extraction method of selected samples additionally we analyzed down core samples of the planktonic foraminifera turborotalita quinqueloba and globorotalia inflata for their ba ca ratios these analyses which were performed for the first time on these species were used to reconstruct past oceanic ba concentrations we suggest that in the study area which is characterized by high accumulation rates the preserved toc content is a valuable proxy for past primary productivity whereas the solid phase batot contents appear to be affected by other mechanisms and factors peaks of total barium content in the clay fraction and of ba ca ratios in the planktonic foraminifera shells found during the younger dryas and the heinrich 1 event are likely to result from increased meltwater influx into the northern north atlantic we suggest that ba enriched meltwater was transmitted by the eastern boundary current system from higher latitudes to the region of the canary islands total barium contents of the clay fraction batot clay and ba ca in planktonic foraminifera shells seem to be reliable proxies for this discharge of meltwater

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

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

carbon and oxygen isotope composition of globigerinoides ruber in two deep sea cores from the levantine basin eastern mediterranean abstract carbon and oxygen isotope analyses have been carried out on 114 samples of globigerinoides ruber from two deepsea cores ban 82 15 pc and ban 82 18 gc raised on the outer slopes of the mediterranean ridge these cores 1050 and 462 cm long respectively contain the sedimentary history of the eastern mediterranean in the last 300 000 years and include sapropelitic layers s 1 to s 10 the climatic fluctuations recorded by the isotopic signal are in general well correlatable with those obtained in previous studies on the mediterranean quaternary most sapropelitic intervals correspond to warm climatic conditions with a maximum recorded in core 15 pc at approximately 125 000 yrs b p isotope stage 5e only s 6 and partially s 8 reflect glacial conditions thus indicating the existence of an alternative model for the deposition of organic rich layers the magnitude of fluctuations in oxygen isotope composition about 7 is unusually wide for the eastern mediterranean and the record is generally shifted toward negative values for approximately 1 this is probably due to the nile discharge that strongly affects these levantine basin cores oxygen and carbon curves are in phase showing the large influence of organic productivity on the carbon isotope composition

stratigraphy of the western mediterranean and southern calabrian ridges eastern mediterranean abstract the present paper illustrates the stratigraphic results of a transponder navigated coring program carried out in 1978 on the southern calabrian ridge cobblestone area 4 and western mediterranean ridge cobblestone area 3 semi quantitative investigations of over 600 foraminiferal samples and 450 nannofossil slides from forty cores with a total recovery of 333 m comprise the data base of the study most of the sediments recovered are late pleistocene or holocene in age the high resolution nannofossil biostratigraphic scheme recently proposed for the quaternary coupled with sapropel stratigraphy and with tephrachronology resulted in precise correlation of the cores mid pleistocene sediments were recovered in a single core from area 4 and in one core from area 3 both located on basin walls four cores from basin walls in area 4 yielded pliocene sediments no sediments older than approximately 3 m y foraminiferal zone m pl 4 reticulofenestra pseudoumbilica nannofossil zone are exposed on the explored walls from the southern calabrian ridge early and late pliocene sediments were recovered from the walls of the deepest crater like basin explored in area 3 but only in dredges in this latter area also two peculiar lithologies were cored basically unfossiliferous but thought to be pre pliocene in age a mud breccia whose clasts yield a sparse assemblage of mid cretaceous planktonic foraminifera and a dolomitic mudstone which is attributed to the late messinian on the basis of correlation with a similar lithology cored at dsdp site 374 and substantiated by analogy in x ray controlled mineralogical composition the fairly complete record of late pleistocene and holocene sapropels recovered in the southern calabrian ridge discards the hypothesis that the southern part of the ionian sea did not undergo stagnant cycles during the ice ages another hypothesis relating the origin of cobblestone topography to olistostromes is also considered untenable on the basis of the new data the large number of cores precisely located on a previously mapped highly irregular bottom physiography disproves that large scale chaotic sedimentation occurred debris flows recorded in base of slope cores document local slope failures

orbital and sub orbital scale climate impacts on vegetation of the western mediterranean basin over the last 48 000 yr article i nfo high resolution pollen analysis of alboran sea core md95 2043 provides a 48 ka continuous vegetation record that can be directly correlated with sea surface and deep water changes the reliability of this record is supported by comparison with that of padul sierra nevada spain marine isotope stage mis 3 was characterised by fluctuations in quercus forest cover in response to dansgaard oeschger climate variability mis 2 was characterised by the dominance of semi desert vegetation despite overall dry and cold conditions during mis 2 heinrich events hes 2 and 1 were distinguished from the last glacial maximum by more intensely arid conditions taxon specific vegetation responses to a tripartite climatic structure within the hes are observed in mis 1 the bolling allerod was marked by rapid afforestation while a re expansion of semi desert environments occurred during the younger dryas the maximum development of mixed quercus forest occurred between 11 7 and 5 4 cal ka bp with forest decline since 5 4 cal ka bp on orbital timescales a long term expansion of semi desert vegetation from mis 3 into mis 2 reflects global ice volume trends while holocene arboreal decline reflects summer insolation decrease the influence of precession on the amplitude of forest development and vegetation composition is also detected

paleotemperature and paleosalinity history of the estern mediterranean during the late quaternary abstract faunal and isotopic studies of continuous deep sea cores were used to determine the paleotemperature and paleosalinity history of the eastern mediterranean for the last 500 000 years temperature related changes in the planktonic foraminiferal assemblages appear to be synchronous with glacial interglacial changes in the open ocean the oxygen isotopic records reveal fluctuations of up to 5 much higher than the average open ocean glacial interglacial amplitude the abnormally high depletions in both 18 o and 13 c are consistently associated with sapropel layers and they are considered to be due to reduced surface salinities the apparent phase difference between the isotopic and faunal records for stages 1 7 last 250 000 years does not represent real temporal leads or lags but is due instead to regional salinity changes in the isotopic record superimposed on the global ice volume effect a detailed study of termination ii 127 000 yr b p in a core east of crete reveals a distinct set of paleoceanographic events associated with this rapid deglaciation these include 1 a rapid increase in surface water temperatures at about 127 000 yr b p 2 the deposition of sapropel d at about 125 000 yr b p 3 a localized increase in surface productivity also at 125 000 yr b p and 4 the return to normal open marine conditions by about 120 000 yr b p

circulation changes and nutrient concentrations in the late quaternary aegean sea a nonsteady state concept for sapropel formation sapropel forming conditions we identify the start of seasonal stratification and highlight a lag in d 18 o response of the planktonic foraminifer n pachyderma to termination t1b as identified in the d 18 o record of g ruber by use of a simple model we determine that this offset cannot be a function of bioturbation effects the lag is of the order of 1 kyr and suggests that isolation of intermediate deep water preceded the start of sapropel formation by up to 1 5 kyr using this discovery we propose an explanation for the major unresolved problem in sapropel studies namely the source of nutrient supply required for export productivity to reach levels needed for sustained sapropel deposition we suggest that nutrients had been accumulating in astagnant basin for 1 1 5 kyr and that these accumulated resources wereutilized duringthe deposition of s1 in addition we provide a first quantitative estimate of the diffusive 1 e mixing timescale for the eastern mediterranean in its stratified sapropel mode which is of the order of 450 years index terms 1050 geochemistry marine geochemistry 4835 4850 3030 marine geology and geophysics micropaleontology 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 4267 oceanography general paleoceanography 4870 oceanography biological and chemical stable isotopes keywords sapropel mediterranean holocene foraminifera climate variability

calcareous nannofossils planktonic foraminifera and oxygen isotopes in the late quaternary sapropels of the ionian sea core m 25 4 12 a long piston core 12 20 m recovered in the ionian sea during cruise m25 4 of the r v meteor summer 1993 at a water depth of 2467 m shows an almost complete sequence of sapropels s 1 s 3 to s 10 over the last 330 ka this paper presents the results of an integrated study based on quantitative biostratigraphic analyses performed on both calcareous nannofossils and planktonic foraminifera coupled with the 18o record a decrease in syracosphaera sp 1 and an increase in the abundance of the genus rhabdosphaera and of helicosphaera carteri florisphaera profunda and of the reworked specimens has been found in the calcareous nannofossil assemblage within the sapropels the planktonic foraminiferal assemblage of the sapropels is characterized by a peak in the frequency of globigerinoides ruber var alba and rosea and neogloboquadrina dutertrei the 18o record of globigerinoides ruber and globigerina bulloides allows recognition of isotope stages 1 to 9 and shows a negative fluctuation that corresponds to the sapropel layers these features support the idea of increased productivity coupled to the presence of reduced salinity surface waters that caused the deposition of the sapropels however the need for a good understanding of the ecological requirements of modern assemblages is stressed this is necessary to correctly interpret fossil assemblages this in turn will allow a better understanding of the palaeoceanographic conditions leading to sapropel deposition

response of benthic foraminifera to stagnant episodes a quantitative study of core ban 81 23 eastern mediterranean abstract the core investigated was raised from the floor of the ares crater in the western mediterranean ridge cobblestone area 3 at 35 52 03 n 20 47 46 e at a water depth of 3026 m forty one samples were taken from beneath within and above seven sapropel layers identified as s 1 s 3 s 4 s 5 s 6 s 7 and s 8 and two tephra layers ranging in age from approximately 5000 to approximately 250 000 years b p our study shows that the cyclically repeated stagnant episodes resulted in a strong reduction of the faunal density due to the basinal setting some displaced elements were recorded in resedimented beds anomalinoides minimus displays peak abundances in post sapropel layers thus supporting the interpretation that it is an opportunistic species suitable for a rapid repopulation of the bottom after a stagnant episode this taxon along with eponides tumidulus articulina tubulosa and to a lesser extent miliolinella subrotunda dominates the autochthonous deep water fauna other taxa are recorded in high percentages only at definite stratigraphic levels they are epistominella vitrea beneath s 6 and cassidulina laevigata beneath s 1 we consistently recorded a sparse faunule within the sapropels consisting of shallow water epiphytic rotaliforms interpreted as allochthonous transported by floating algae associated with bolivina spp and anomalinoides minimus the occurrence of bolivina spp and of buliminids in general within the sapropels is accounted for by their capability of tolerating very low oxygen levels the topmost part of the multilayered sapropel s 6 in particular is rich in bulimina exilis cassidulinoides tenuis and ellipsopolymorphina sp this sapropel which unlike the other ones originated during glacial conditions is preceded by peak abundances of faunal density a strong increase in productivity of the bottom living fauna is inferred and supported by similar findings in a nearby plateau core where drastic changes in density and diversity are recorded

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

a comparison between excess barium and barite as indicators of carbon export 1 since dymond et al 1992 proposed the paleoproductivity algorithm based on bio ba which relies on a strong correlation between ba and organic carbon fluxes in sediment traps this proxy has been applied in many paleoproductivity studies barite the main carrier of particulate barium in the water column and the phase associated with carbon export has also been suggested as a reliable paleoproductivity proxy in some locations we demonstrate that baexcess total barium minus the fraction associated with terrigenous material frequently overestimates babarite barium associated with the mineral barite most likely due to the inclusion of barium from phases other than barite and terrigenous silicates e g carbonate organic matter opal fe mn oxides and hydroxides a comparison between overlying oceanic carbon export and carbon export derived from baexcess shows that the dymond et al 1992 algorithm frequently underestimates carbon export but is still a useful carbon export indicator if all caveats are considered before the algorithm is applied babarite accumulation rates from a wide range of core top sediments from different oceanic settings are highly correlated to surface ocean 14 c and chlorophyll a measurements of primary production this relationship varies by ocean basin but with the application of the appropriate f ratio to 14 c and chlorophyll a primary production estimates the plot of babarite accumulation and carbon export for the equatorial pacific atlantic and southern ocean converges to a global relationship that can be used to reconstruct paleo carbon export index terms 3022 marine geology and geophysics marine sediments processes and transport 4267 oceanography general paleoceanography 4825 oceanography biological and chemical geochemistry keywords paleoproductivity barite export production excess barium marine sediments citation eagle m a paytan k r arrigo g van dijken and r w murray a comparison between excess barium and barite as indicators of carbon export paleoceanography 18 1 1021 doi 10 1029 2002pa000793 2003

geochemical studies of the recent sapropel and associated sediment from the hellenic outer ridge eastern mediterranean sea i mineralogy and chemical composition abstract the mineralogy major and minor element geochemistry and the accumulation rate of a single kastenlot core from the eastern mediterranean is reported the sapropel is similar mineralogically and in its major element composition to the associated marl ooze and calcareous clay it differs from these sediments in having higher concentrations of ba cr cu mo ni sr and zn and lower concentrations of mn the enrichments are explained by increased fertility ba organic matter or sulphide association cr cu mo ni and zn and the presence of aragonitic pteropods sr the organic material has a marine origin based on the carbon isotopic value 13 c 20 and c n ratio 10 the sapropel accumulated 3 to 5 times faster than the associated sediments in this particular core the evidence is consistent with the formation of this sapropel by an increased flux of carbon to the sea floor this would have been caused by increased marine primary production in the eastern mediterranean during periods of reversed circulation brought about by high post glacial runoff primarily from northern africa the additional carbon flux would have lowered the oxygen levels of the bottom waters but it is not known whether anoxic conditions ensued or whether they would have been necessary to preserve the deposited carbon

after the deluge mediterranean stagnation and sapropel formation in an east mediterranean marine core the upper sapropel begins soon after the start of a global event a very heavy precipitation which occurred in the equatorial latitudes during the late glacial early holocene this heavy precipitation in africa channelled by the nile river across 35 of latitude produced a low salinity surface layer in the east mediterranean in this confined basin with high bottom salinity the steep salinity gradient stratified the water column the stagnant bottom waters triggered the sapropel formation cretaceous sapropels in the tropical oceans may result from the same chain of events in warm humid climates with contrasting wet and dry seasonal rhythm

sahel megadroughts triggered by glacial slowdowns of atlantic meridional overturning 1 the influence of the large scale ocean circulation on sahel rainfall is elusive because of the shortness of the observational record we reconstructed the history of eolian and fluvial sedimentation on the continental slope off senegal during the past 57 000 years our data show that abrupt onsets of arid conditions in the west african sahel were linked to cold north atlantic sea surface temperatures during times of reduced meridional overturning circulation associated with heinrich stadials climate modeling suggests that this drying is induced by a southward shift of the west african monsoon trough in conjunction with an intensification and southward expansion of the midtropospheric african easterly jet

calcareous nannofossil paleoecology in the sapropel s1 of the eastern ionian sea paleoceanographic implications a high resolution study performed by means of calcareous nannofossils on two box cores located in the south eastern ionian basin allowed recognition of fluctuations in the assemblage which can be related to the climatic and paleoceanographic changes that occurred during the deposition of the holocene sapropel s1 this study reports a decrease of the coccolith abundance and of the genus reticulofenestra in the s1 sapropel interval considered as whole with its mn and fe oxidized intervals florisphaera profunda shows an increase at the base of the dark corg rich interval while helicosphaera carteri and rhabdosphaera claviger show an increase in abundance within the fe enriched interval of the oxidized sapropel braarudosphaera bigelowii is very rare in the interval studied as a whole however it shows a small but significant increase in abundance in the mn enriched interval of the oxidized sapropel sapropel deposition is probably related to important climatic changes that influenced the abundance of the various nannofossil species as a function of their paleoecological preferences our results indicate that three different paleoceanographic phases exist in s1 suggesting eutrophication at the beginning of s1 deposition followed by an intermediate stage characterized by nutrient depletion and finally by stagnation

turbidites and megaturbidites from the herodotus abyssal plain eastern mediterranean unrelated to seismic events abstract a transect of 9 piston and gravity cores was taken across the southeast flank of the mediterranean ridge the transect extends from the abyssal plain to a location 290 m shallower than the abyssal plain and 50 km north of the edge of the ridge each core contains two or more turbiditic layers which belong to two discrete types here called a and b type a essentially consists of black plastic clays rich in smectite with silt fraction of terrigenous nature source area is the nile cone and age is middle or late pleistocene type b turbidites are pale brown to whitish in color coarse grained carbonate rich and bioclastic in composition with shallow water fossils dominant they are poor in smectite and the silt fraction is very rich in carbonates calcite and aragonite the source area is the north african shelf south of the abyssal plain a megabed belonging to type b turbidites is correlatable from core to core with a thickness in excess of 10 m in the abyssal plain and an estimated volume of 10 km 3 its stratigraphic position in the latest pleistocene suggests that its origin is related to a sudden collapse of bioclastic sediments accumulated in a canyon head during a low sea level stand the source areas of the two discrete turbidite types belong to the essentially aseismic north african continental margin although they are presently recorded on the tectonically active mediterranean ridge no seismic events are required to account for the presence of either type of turbidite

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

calcareous nannofossils and the origin of eastern mediterranean sapropels a quantitative analysis of calcareous nannofossil assemblages was carried out with an optical microscope on four deep sea cores raised from the eastern mediterranean and selected to form a nw se transect a total of 748 samples were studied including a very detailed analysis of sapropels s5 and s6 in two out of the four cores this paper is restricted to the discussion of the results obtained on florisphaera profunda which provided important insights on the mechanisms of sapropel formation an intricated and unravelled puzzle for the scientists of the last decades on the basis of abundance variations of f profunda the only species of calcareous nannoplankton which inhabits the lower part of the photic zone i suggest that sapropel formation was triggered by increased primary production either confined to a deep chlorophyll maximum dcm a concept previously introduced by rohling and gieskes 1989 or extended to a thicker layer of the photic zone when increased primary production was confined to the dcm sapropel s3 s4 s5 s7 and s1 this latter only in the eastern part of the basin the abundance of f profunda was enhanced greatly with respect to all other species living in the higher part of the photic zone on the contrary when the increased primary production was extended to a thicker layer of the photic zone glacial sapropels s6 and s8 the production of most nannoplankton species was favored decreasing the relative proportion of f profunda

organic carbon variations of the eastern mediterranean holocene sapropel a key for understanding formation processes abstract this work reports on the organic carbon content of the s1 holocene sapropel the youngest and most extensively researched of the eastern mediterranean sapropels the peak organic carbon percentage of the s1 sapropel varies between 1 2 and 3 4 at varying locations these variations could not be correlated with sapropel thickness or with spatial location in contrast there was a close linear correlation with water depth the deeper samples containing the highest values of organic carbon within the s1 layer the highest values were found in the top of the sapropel even if primary productivity increased during the s1 sapropelic period the main factors responsible for sapropel deposition were changes in the degradation and preservation of organic matter in the water column and at the sediment water interface water column stratification created an oxygenated surficial layer 0 350 400 m thick and a stagnant deep water layer the majority of the organic material escaping the surficial layer was remineralised either at the sediment water interface or just below it organic matter preserved in sapropelic sediments can be assumed to have remained for a significantly longer time 1000 years within the benthic boundary layer than in the water column organic flux decreased with depth through the stagnant deep water layer when stagnation was established water exchanges either did not exist or were limited vertical oxidant transport depended on eddy diffusion while oxidant fluxes at the sediment water interface decreased with depth the organic matter mineralisation rate also decreased and the burial efficiency increased the linear relationship between sapropel organic content and depth was reflected in a linear decrease in oxidant flux regardless of location the same organic carbon percentage was preserved at the same depth in contrast in the same area but at different depths organic carbon content ranges between 1 2 and 3 4 this observation suggests that primary productivity was of the same order of magnitude basinwide the organic carbon concentration of sediment should be used with caution as a quantitative record of palaeoproductivity

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

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

abrupt temperature changes in the western mediterranean over the past 250 000 years a continuous high resolution western mediterranean sea surface temperature sst alkenone record spanning the past 250 000 years shows that abrupt changes were more common at warming than at cooling during marine isotope stage mis 6 sst oscillated following a stadial interstadial pattern but at lower intensities and rates of change than in the dansgaard oeschger events of mis 3 some of the most prominent events occurred over miss 5 and 7 after prolonged warm periods of high stability climate during the whole period was predominantly maintained in interglacial interstadial conditions whereas the duration of stadials was much shorter

late quaternary pelagic sedimentation on the southern calabrian ridge and western mediterranean ridge eastern mediterranean abstract cores from plateaus lying some 150 200 m above the basin floors in areas of strong vertical relief visited during the cobblestone project consist entirely of pelagic marls with sapropels and tephras as minor lithologies all the plateau cores were correlated by means of isochronous lithologies and biostratigraphically calibrated a core from area 3 no 29 and two cores from area 4 no 45 and 6 were selected as reference sections and studied quantitatively in terms of grain sizes carbonate content and microfossil content faunal curves based on selected species of planktonic foraminifers correlate between the three cores which extend back in time to approximately 185 000 yr for area 4 and to 430 000 yr for area 3 winnowing resulted in a reduced sedimentation rate in area 3 in unusually high percentages of the coarser sediment fraction and in extended hiatuses at the top of the cores the highest temperature in surficial waters as indicated by the foraminiferal faunas is recorded in all three references sections at the base of an interval correlative with isotopic stage 5e 125 000 yr b p within sapropel s 5 clay mineralogy indicates basically uniform conditions in the two areas with the exception that smectite is more abundant in the calabrian ridge which is closer to its source area sicily sicily channel carbonates include calcite magnesian calcite and some dolomite sapropels sedimentary expression of stagnation represent up to 25 of the sedimentary column in an interval encompassing isotopic stage 5 through 7 the average organic carbon content in analysed sapropels is 3 1 versus 0 29 in normal pelagic sediments sapropels s 6 and s 8 are consistently accompanied by a foraminiferal fauna that is indicative of low salinity cool surficial waters whereas sapropels s 1 s 5 and s 7 occur in coincidence with the warmest peaks of the climatic faunal curve average sedimentation rate is 3 2 cm 1000 yr for core 29 5 5 cm 1000 yr for core 45 sedimentation rates calculated for basin cores are five to ten times higher sedimentation rates of sapropels and tephras are independent from regional sedimentation rates hiatuses in plateau cores correlate with debris flows in base of slope cores both occurring during times of enhanced bottom circulation and submarine erosion related to low stands of sea level in cold periods

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

marine productivity changes during the end permian crisis and early triassic recovery abstract the latest permian mass extinction lpme coincided with major changes in the composition of marine plankton communities yet little is known about concurrent changes in primary productivity earlier studies have inferred both decreased and increased productivity in marine ecosystems immediately following the end permian crisis here we assess secular and regional patterns of productivity variation during the crisis through an analysis of the burial fluxes of three elemental proxies total organic carbon toc phosphorus p and biogenic barium babio primary productivity rates appear to have increased from the pre crisis late permian through the early triassic in many parts of the world although the south china craton is unusual in exhibiting a pronounced decline at that time most of the 14 permian triassic study sections show concurrent increases in sediment bulk accumulation rates suggesting two possible influences linked to subaerial weathering rate changes 1 intensified chemical weathering resulting in an increased riverine flux of nutrients that stimulated marine productivity and 2 intensified physical weathering leading to higher fluxes of particulate detrital sediment to continental shelves thus enhancing the preservation of organic matter in marine sediments an additional factor especially in the south china region may have been the intensified recycling of bacterioplankton derived organic matter in the ocean surface layer reducing the export flux rather than primary productivity per se the ecosystem stresses imposed by elevated fluxes of nutrients and particulate sediment as well as by locally reduced export fluxes of organic matter may have been important factors in the 2 to 5 million year long delay in the recovery of early triassic marine ecosystems

holocene palaeohydrology and climate variability in northeastern spain the sedimentary record of lake estanya pre pyrenean range abstract this multi proxy study of sediment cores from karstic lake estanya pre pyrenean range ne spain provides the first complete continuous record of the hydrological evolution in the northeastern iberian peninsula over the last 9500 yr six sedimentary facies and four main sedimentary units have been defined after integration of sedimentological mineralogical and geochemical analyses the use of total sulphur content and sedimentary facies as paleohydrological proxies allows reconstruction of relative changes in lake level the estanya record shows a large increase in water availability after 9 2 ka fluctuating lake levels and salinity during the period 9 2 4 2 ka and generally higher lake levels after 1 7 ka periods of increased run off and sediment delivery and less saline conditions occurred at 8 5 8 2 6 7 5 9 and 4 9 4 2 ka dominant lower lake levels and concentrated waters during the period 4 2 0 8 ka were punctuated by a higher lake level higher clastic input episode ca 1 7 1 ka fluctuating but higher lake levels occurred during the last 800 years the main hydrological phases in lake estanya are coherent with western mediterranean and north atlantic holocene reconstructions but they also show similarities with northern african records

extensional tectonics of the toledo ductile brittle shear zone central iberian massif abstract the toledo mylonite in the central area of the iberian massif represents a major ductile shear zone only a small part of which has been exposed to view mylonites derived largely from migmatite occupy a 300 350 m thick gently s dipping zone along the southern margin of the toledo crystalline massif the upper plate comprises palaeozoic lower grade metasedimentary rocks intruded by a late hercynian pluton the juxtaposition of the upper and lower plates with different structural and metamorphic conditions indicates that the shear zone is a significant structure with a large displacement progressive simple shear under conditions of a clearly decreasing confining pressure and temperature is supported by a microbrecciated mylonite cataclasite and ultracataclasite sequence overlying the mylonites the top of the ledge of cataclasites corresponds to the detachment fault part of the shear zone structural relations combined with meso and micro structural evidence stretching lineations and asymmetric shear sense indicators support the conclusion that the mylonites and cataclasites associated with the detachment faulting formed during a continuous extensional deformation detachment fault models developed for the formation of metamorphic core complexes can be applied in the toledo massif we propose a model that implies a transition from ductile to brittle deformation associated with extension at greater structural depths during lower permian time

late quaternary climatic changes on the southwestern balearic slope western mediterranean isotopic faunal and mineralogical relationships abstract we report the results of a research on the carbonate mineralogy planktonic foraminifera distribution and oxygen and carbon isotope composition of g bulloides in hemipelagic carbonate oozes of the southwestern balearic slope western mediterranean to contribute to the understanding of climatic and ecological variations during the last quaternary interglacial glacial cycle and their influences on the carbonate sedimentary processes of the western mediterranean oxygen isotope stages 1 2 and 3 have been identified and correlated to those established in tyrrhenian cores the carbon isotope records display several anomalies which are explained by productivity variations and diagenetic processes pelagic carbbonates low mg calcite and aragonite and detrital minerals quartz high mg calcite and dolomite display variations that are climate related pelagic carbonates increase during warm intervals while intense low mg calcite dissolution and greater quantities of detrital minerals are found in colder intervals our results suggest that the carbonate distribution of the western mediterranean correlates to the reported from the atlantic ocean nevertheless the molar mgco3 content in low mg calcite disagree to the established temperature relationship in other oceans

synchronisation of palaeoenvironmental events in the north atlantic region during the last termination a revised protocol recommended by the intimate group abstract the north atlantic intimate group of the inqua palaeoclimate commission has previously recommended an event stratigraphy approach for the synchronisation of records of the last termination using the greenland grip isotopic record as the regional stratotype and intcal98 for the calibration of radiocarbon dates lowe j j hoek w intimate group 2001 inter regional correlation of palaeoclimatic records for the last glacial interglacial transition a protocol for improved precision recommended by the intimate project group quaternary science reviews 20 1175 1187 here we present a revised protocol for time stratigraphic correlation in the north atlantic region over a more extended time period 30 8 ka this employs the new ngrip isotopic record and associated greenland ice core chronology 2005 gicc05 as the regional stratotype intcal04 for the calibration of radiocarbon dates bayesian based statistical procedures for the construction of age models and tephrochronology to validate correlations between regional site records

floral and solution patterns of coccoliths in surface sediments of the north pacific coccolith assemblages from core top samples of the north pacific seafloor follow the distribution of surface water masses gephyrocapsa caribbeanica umbellosphaera tenuis and coccolithus pelagicus are the most important identifiers of surface water mass different multivariate statistical techniques group shallow samples in somewhat different spatial patterns factor analysis condenses the information contained in sixteen ies percentages to four new variables that can be interpreted as species assemblages by canonical correlation analysis these assemblages can in turn be related to the environment the first canonical correlation indicates that factor 2 the g caribbeanica assemblage is represented in samples underlying cooler surface water a second possible correlation describes a direct relationship between factor 3 the umbilicosphaera sibogae assemblage and the remaining environmental variable surface water salinity factor 1 the g oceanica assemblage and factor 4 the emiliania huxleyi assemblage are not as closely related to the selected environmental measures of temperature salinity dissolved oxygen and inorganic phosphate phosphorus as are factor 2 and factor 3 because samples were coded according to their overlying water mass group separations produced by discriminant analysis are easily interpreted in terms of the environment overlap of group assignments occurs for samples from the south china sea and extreme western pacific even partially dissolved samples retain the signature of surface water mass group assignment for those samples is generally reliable with the exception of samples from the central water mass where almost half of the shallow and half of the deep samples show strongest affinities with one of the other three water masses selective solution therefore only partially obscures the record of floral provinciality partial dissolution of coccolith assemblages does not proceed according to one systematic rank order the sequence of species removal is variable from region to region the more abundant species tend to consistently appear at an extreme of the ranking for example umbilicosphaera sibogae is among the least resistant and c leptoporus and g oceanica are among the most resistant species maximum depths of coccolith lysocline and compensation depth occur generally in the central part of the basin and shoal towards its margins as previously observed for planktonic foraminifera

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

connection between south mediterranean climate and north african atmospheric circulation during the last 50 000 yr bp north atlantic cold events abstract high resolution clay mineralogical analyses were performed on sediment deposited during the last 50 000 yr in the alboran sea odp site 976 the clay mineral record is compared with pollen assemblages and with annual precipitation pann and mean temperatures of the coldest month mtco reconstructed with the modern analog technique mat enhanced contribution of palygorskite a typical wind blown clay mineral characterizes the north atlantic cold climatic events coeval development of the semi arid vegetation artemisia rich associated with a drastic fall of reconstructed precipitations and temperatures suggest cold and arid continental conditions in the west mediterranean area during north atlantic cold events the clay mineral association especially the palygorskite content and the illite to kaolinite ratio indicate western morocco as one of the major source of the clay size fraction during the north atlantic cold events the maximum abundance of artemisia associated with the presence of argania pollen both indicate morocco as the main origin for pollen during these cold periods the comparison of these pollen and clay mineral specific features allows us to pinpoint western morocco as the dominant source of wind blown particles during north atlantic cold events these specific mineralogical composition and palynological assemblages reveal enhanced aridity over north africa and intensification of winds favouring dust erosion and transport from north africa toward the alboran sea during the north atlantic cold events according to atmospheric models such a meridian transport 1 likely results from the development of strong and stable anticyclonic conditions over the tropical atlantic and north africa similar to today s summer meteorological configuration and 2 implies a northward position of the westerly winds during north atlantic cold events finally the synoptic situation over the west mediterranean during the north atlantic cold events is compared with the north atlantic oscillation nao suggesting that during the cold atlantic events weather regimes over europe and north africa may have been systematically shifted towards a positive nao situation

climatic forcing of eastern mediterranean deep water formation and benthic ecosystems during the past 22 000 years abstract lateglacial and holocene faunal and stable isotope records from benthic foraminifers in the eastern mediterranean sea ems suggest a high spatiotemporal variability of deep water oxygenation and biogeochemical processes at the sea floor during that time changes in the oxygenation and food availability of the deep sea ecosystems are closely linked to the hydrology of the ems borderlands they reflect orbital and suborbital climate variations of the high northern latitudes and the african monsoon system during the last glacial maximum cool surface waters and high evaporation resulted in maximum convection and oxic deep waters in all sub basins strong wind induced mixing fostered surface water production with seasonal phytodetritus fluxes during the glacial termination and the holocene oxygenation and food availability of deep sea benthic ecosystems were characterized by a pronounced regional differentiation local deep water formation and trophic conditions were particularly variable in the northern aegean sea as a response to changes in riverine runoff and black sea outflow during the interval of sapropel s1 formation in the early holocene average oxygen levels decreased exponentially with increasing water depth suggesting a basin wide shallowing of vertical convection superimposed by local signals in the northernmost aegean sea deep water ventilation persisted during the early period of s1 formation owing to temperature driven local convection and the absence of low salinity black sea outflow at the same time severe temporary anoxia occurred in the eastern levantine basin at water depths as shallow as 900 m this area was likely influenced by enhanced nutrient input of the nile river that resulted in high organic matter fluxes and related high oxygen consumption rates in the water column in the southern aegean and levantine seas we observe a gradual increase in deep water residence times preceding s1 formation by approximately 1 1 5 kyr once oxygen levels fell below a critical threshold the benthic ecosystems collapsed almost synchronously with the onset of s1 deposition the recovery of benthic ecosystems during the terminal phase of s1 formation is controlled by subsequently deeper convection and re ventilation over a period of approximately 1500 years after the re ventilation of the various sub basins had been completed during the middle and late holocene deep water renewal was more or less similar to recent rates during that time deep sea ecosystem variability was driven by short term changes in food quantity and quality as well as in seasonality all of which are linked to millennial scale changes in riverine runoff and associated nutrient input