organic geochemistry and origin of late glacial holocene sapropelic layers and associated sediments in marmara sea abstract organic geochemistry of two sapropel sapropelic sediment units dated 10 6 6 4 and 3 8 3 2 kyr bp and associated sediments in two gravity cores from the marmara sea were studied to characterize the organic matter and discuss its paleoceanographic implications vertical trends of c n ratio 13c and hydrogen indices show that the flooding of the marmara sea by the mediterranean waters at 12 kyr bp and onset of deposition of the lower sapropelic layer at 10 6 yr bp are characterized with a high input of terrestrial organic matter this terrestrial input decreased and marine organic matter contribution increased in time towards the top of the upper sapropelic layer at 3 2 kyr bp the lower sapropelic layer is broadly the same age and has a similar distribution of organic matter type as the s1 sapropel of the aegean sea suggesting their depositions may have been controlled by the same events both the lower marmara sapropelic layer and the aegean s1 sapropel were probably deposited during a time of high influx of organic rich river waters from the black sea this influx of black sea water could have induced water stratification in the marmara sea and aegean sea and lead to the deposition of the sapropels

organic rich layers in the metochia section gavdos greece evidence for a single mechanism of sapropel formation during the past 10 my abstract three well developed 10 ma old sapropels from the island of gavdos greece were selected for a detailed geochemical micropaleontological and sedimentological study the sapropels are characterized by a high organic carbon and a low carbonate content productivity was higher during sapropel formation as indicated by increased ba contents and higher percentages of the planktonic foraminiferal species neogloboquadrina acostaensis enrichment of mo and v in the sapropels indicates less oxygenated bottom water conditions which is supported by the flourishing of low oxygen tolerant benthic foraminifera variation in grainsize and the ti al ratio point to an alternating dominance of fluvial sapropels and eolian derived homogeneous intervals terrigenous clastics evidence for a local origin of the enhanced fluvial input comes from the gradual replacement of the sapropels by cyclic turbidite sequences which were fed by bed load type rivers the increased fluvial input during sapropel formation increased the sedimentation rate and caused the observed carbonate depletion the results obtained for the gavdos sapropels are consistent with those of previous studies of younger sapropels and related caco 3 cycles in the mediterranean the consistency in most of the geochemical and micropaleontological characteristics indicates that all sapropels and related layers are the result of a single mechanism for at least the past 10 my namely precession induced dry wet oscillations in the mediterranean climate still the effect of this mechanism on the intensity of surface water productivity dilution and diagenetic signals may differ from site to site depending on location depositional environment and intensity of the astronomical forcing

spatial productivity variations during formation of sapropels s5 and s6 in the mediterranean sea evidence from ba contents abstract we investigated five time equivalent core sections 180 110 kyr bp from the balearic sea menorca rise the easternmost levantine basin and southwest south and southeast of crete to reconstruct spatial patterns of productivity during deposition of sapropels s5 and s6 in the mediterranean sea our indicators are ba total organic carbon and carbonate contents we found no indications of ba remobilization within the investigated core intervals and used the accumulation rate of biogenic ba to compute paleoproductivity maximum surface water productivity up to 350 g c m2 yr was found during deposition of s5 isotope stage 5e but pronounced spatial variability is evident coeval sediment intervals in the balearic sea show very little productivity change suggesting that chemical and biological environments in the eastern and western mediterranean basins were decoupled in this interval we interpret the spatial variability as the result of two different modes of nutrient delivery to the photic zone river derived nutrient input and shoaling of the pycnocline nutricline to the photic zone the productivity increase during the formation of s6 was moderate compared to s5 and had a less marked spatial variability within the study area of the eastern mediterranean sea given that s6 formed during a glacial interval glacial boundary conditions such as high wind stress and or cooler surface water temperatures apparently favored lateral and vertical mixing and prevented the development of the spatial gradients within the eastern mediterranean sea ems observed for s5 a non sapropel sediment interval with elevated ba content and depleted 18o 16o ratios in planktonic foraminifer calcite was detected between s6 and s5 that corresponds to the weak northern hemisphere insolation maximum at 150 kyr at this time productivity apparently increased up to five times over surrounding intervals but abundant benthic fauna show that the deep water remained oxic following our interpretation the interval denotes a failed sapropel when a weaker monsoon did not force the ems into permanent stratification the comparison of interglacial and glacial sapropels illustrates the relevance of climatic boundary conditions in the northern catchment in determining the facies and spatial variability of sapropels within the ems

paleoclimate and paleoceanography over the past 20 000 yr in the mediterranean sea basins as indicated by sediment elemental proxies abstract marine sediments record paleoenvironmental changes over time through variations in major and trace element concentrations the main objective of this paper is to review such changes in the mediterranean sea basins over the last 20 ka using the inorganic chemistry and mineralogy of marine sediment records elemental ratio proxies that are mostly used are discussed and the uncertainties involved in using them for paleoclimate and paleoceanographic reconstructions are evaluated the focus on the mediterranean region is based on the sensitivity of this region to global climate changes due to its semi enclosed nature the elemental ratios that have been particularly useful for reconstructing terrigenous inputs into the mediterranean have been ti al and zr al ratios as proxies for eolian dust input and mg al k al and rb al ratios as proxies for fluvial input redox sensitive elements e g u mo v co ni cr have provided reliable reconstructions of oxygen conditions at the time of deposition some of these elements are also particularly susceptible to post depositional remobilization and record diagenetic processes instead of the original environmental signatures regarding productivity fluctuations most of the paleoproductivity reconstructions are based on the abundance of barite and ba excess algorithms the biogeochemistry of ba is however not fully understood and mechanisms for barite precipitation in the water column are not yet known two case studies are presented the eastern mediterranean sapropel s1 deposited between 10 8 and 6 1 cal ka bp and the westernmost mediterranean paleoclimate record over the last 20 ka

biogeochemical assessment of sources of organic matter and paleoproductivity during the early aptian oceanic anoxic event at shatsky rise odp leg 198 this study investigates organic rich sedimentary sequences deposited during the early aptian oceanic anoxic event oae1a at sites 1207 and 1213 on shatsky rise odp leg 198 in the west central pacific biomarker analyses provide evidence of the algal and bacterial origin of organic matter om in these sediments where the abundance of steroidal components particularly sterenes and sterones suggests that the om includes major contributions from eukaryotic sources in an environment characterized by high phytoplankton productivity the presence of alkenones at site 1213b is diagnostic of om derived from representatives of haptophyte algae among the calcareous nannoplankton and their 13c values average 31 6 are consistent with those expected during elevated pco2 the occurrence and prominence of 2 methylhopanes and 2 methylhopanones indicates significant contributions to the om from cyanobacteria which are also likely contributors of hopanoids based on their 13c compositions these biomarker data suggest that oceanic conditions perhaps nitrate or iron limited were conducive to cyanobacteria production during oae1a which appears to distinguish this event from other cretaceous oae

trans mediterranean comparison of geochemical paleoproductivity proxies in a mid pleistocene interrupted sapropel abstract sapropel layers in the sediment record of the mediterranean sea reflect periods of climate induced elevated marine production associated with precessional minima some of these layers feature interruptions that represent centennial to millennial returns to the predominantly low productivity conditions of this sea we have measured multiple geochemical paleoproductivity proxies in the interrupted sapropel layer that corresponds to insolation cycle 90 955 ka at 1 cm intervals in a four site transect from the balearic basin to the levantine basin to assess similarities and differences in its expression at the four locations the interrupted sapropels are similarly divided by an organic carbon poor interval into an upper layer in which organic carbon concentrations reach 2 7 wt and a lower layer in which they peak between 1 and 3 wt the interruption was essentially synchronous in the balearic basin the tyrrhenian basin and the ionian basin but it was delayed and shorter in the levantine basin lighter nitrogen isotope compositions consistently accompany higher organic carbon accumulation rates in the sapropel layers which implies a shift from coccolith dominated organic matter production towards a mode of primary production in which cyanobacteria were important during times of sapropel deposition organic carbon isotopic compositions become heavier as organic carbon accumulation increases at three of the locations which is consistent with elevated productivity however they become lighter at the levantine basin site which suggests greater delivery of isotopically light fluvial waters to this part of the mediterranean sea the local paleoclimate conditions conducive to sapropel formation evidently were not completely uniform across the mediterranean region but their occurrences were synchronous moreover the co existence of an essentially same age interruption of the sapropels at the four locations shows that climate could change rapidly and concordantly across the region at much less than precessional intervals

reconstruction of changes in export productivity during pliocene sapropel deposition a biomarker approach abstract biomarkers alkenones loliolide isololiolide dinosterol and c30 1 15 diol keto ol representative of four major classes of marine primary producers haptophytes diatoms dinoflagellates eustigmatophytes respectively from three sites of an east west transect spanning the entire eastern mediterranean basin were studied for changes in phytoplankton export production before during and after deposition of a pliocene total organic carbon rich up to 27 sapropel 2 943 ma biomarker contents showed substantial differences between non sapropelic and sapropelic sediments in non sapropelic sediments small contents are observed reflecting extensive oxic degradation in oxic pore waters during deposition in the sapropels biomarker accumulation rates showed a substantial increase from the base to the centre likely resulting from increased biological productivity since the bottom waters were continuously anoxic and preservation conditions are similar the diatom biomarker loliolide isololiolide became distinctly more abundant in the sapropels indicating that the eastern mediterranean basin was enriched in nutrients this caused enhanced export production by the major phytoplankton classes leading to periods of sapropel deposition alkenone based sea surface temperature reconstructions indicated that this change in phytoplankton composition was not influenced by changes in sea surface temperature but was mainly nutrient controlled compound specific 13c measurements did not provide additional evidence for substantially increased primary production rates the 13c values of c37 2 alkenones and loliolide isololiolide showed a slightly negative shift instead of the anticipated positive shift this was probably caused by the enrichment of dissolved inorganic carbon in the upper water column caused by enhanced recycling of respired co2 due to the shallow chemocline

modes of sapropel formation in the eastern mediterranean some constraints based on pyrite properties abstract pyrite formation within and directly below sapropels in the eastern mediterranean was governed by the relative rates of sulphide production and fe liberation and supply to the organic rich layers at times of relatively high so2 4 reduction sulphide could diffuse downward from the sapropel and formed pyrite in underlying sediments the sources of fe for pyrite formation comprised detrital fe and diagenetically liberated fe ii from sapropel underlying sediments in organic rich sapropels input of fe from the water column via fe sulphide formation in the water may have been important as well rapid pyrite formation at high saturation levels resulted in the formation of framboidal pyrite within the sapropels whereas below the sapropels slow euhedral pyrite formation at low saturation levels occurred 34s values of pyrite are 33 to 50 below the sapropels 34s is lower than within the sapropels as a result of increased sulphide re oxidation at times of relatively high sulphide production and concentration when sulphide could escape from the sediment the percentage of initially formed sulphide that was re oxidized was estimated from organic carbon fluxes and burial efficiencies in the sediment it ranges from 34 to 80 varying significantly between sapropels increased palaeoproductivity as well as enhanced preservation contributed to magnified accumulation of organic matter in sapropels

extending the astronomical polarity time scale into the miocene an astronomical time scale is presented for the late miocene based on the correlation of characteristic sedimentary cycle patterns in marine sections in the mediterranean to the 65 n summer insolation curve of la90 1 2 with present day values for the dynamical ellipticity of the earth and tidd dissipation by the moon this correlation yields ages for all sedimentary cycles and hence also for the recorded polarity reversals and planktonic foraminiferal and dinoflagellate events the tortonian messinian t m boundary placed at the first regular occurrence of the globorofuliu conomiozea group in the mediterranean is dated at 7 24 ma the duration of the messinian is estimated at 1 91 myr because the miocene pliocene boundary has been dated previously at 5 33 ma 3 the new time scale is confirmed by oar 3gar ages of volcanic beds and by the number of sedimentary cycles in the younger part of the mediterranean messinian

the oxygen and carbon isotope distribution in the mediterranean water masses abstract the oxygen and carbon stable isotope compositions of the present day mediterranean waters have been measured in order to evaluate their variability which is related to the specific climatic and hydrological conditions within the basin the experimental equation between the 18 o value and the salinity of water based on 300 measurements on surface intermediate and deep waters sampled during the vicomed 2 and 3 cruises in the western central and eastern mediterranean has a slope of 0 27 a value which is significantly lower than the slope of 0 45 as defined in the northeast atlantic ocean this difference in the 18 o salinity relationship which occurs immediately in the alboran basin is basically a characteristic of the climatic regime of the mediterranean i e of an excess evaporation over fresh water input the largest variations of these two parameters 18 o of water and 13 c of co 2 are observed in the surface waters mostly in the western mediterranean this evolution mirrors the progressive eastward restriction which separates the less evaporated and more productive western basins from the more evaporated and less productive eastern basins the intermediate waters constitute a homogeneous layer however their 18 o values decrease eastward by 0 35 at maximum due to progressive dilution by mixing with overlying and underlying water masses their 13 c values decrease also eastward by 0 35 at maximum due to an increasing input of nutrients issued from the regeneration of sinking organic particles the deep waters have similar 18 o values but slightly higher 13 c values often by less than 0 1 than the overlying intermediate waters indicating generally well ventilated conditions due to active winter convection

evidence for the evolution of an oxygen minimum layer at the beginning of s 1 sapropel deposition in the eastern mediterranean the sediments of the eastern mediterranean basin contain a series of organic rich sapropels intercalated with organic poor nannofossil oozes until recently the timing of the onset of sapropel formation was not known accurately because of the low resolution achievable by conventional radiocarbon dating compilation of all available 14c ams dates show that the base of s 1 the most recent sapropel was initiated 8800 years b p 14c age corrected by 400 years for reservoir effect under a 500 m water column and moved progressively into deeper water reaching depths of 3500 m at 8200 years b p the linear correlation between the age of s 1 onset and water depth r 0 71 suggests that formation of sapropels moved into deeper water at a rate of 1000 m 200 year a model is suggested in which export production which sank below the well mixed surface layers 500 m was respired consuming dissolved oxygen in the levantine deep water until a threshold value was reached when sapropels began to be preserved in the sediment this resulted in a progressively deepening oxygen minimum zone with time until eventually the entire deep water in the basin was oxygen depleted assuming that the threshold value for sapropel formation was complete anoxia it was calculated that primary productivity in the basin during the deposition of s 1 was a factor of 5 greater than that found at present

precession driven changes in terrestrial organic matter input to the eastern mediterranean leading up to the messinian salinity crisis abstract eastern mediterranean sediments over the past 12 myr commonly show strongly developed precessional cyclicity thought to be a biogeochemical response to insolation driven freshwater input from run off the mediterranean s dominant freshwater source today and in the past is the nile which is fed by north african monsoon rain other smaller circum mediterranean rivers also contribute to mediterranean hydrology crucially run off through all of these systems appears to vary with precession but there is no direct evidence linking individual water sources to the biogeochemical response recorded in mediterranean sediments consequently it is not clear whether the north african monsoon is entirely responsible for the mediterranean s sedimentary cyclicity or whether other precessional signals such as atlantic storm precipitation drive it organic matter in sediments derives from both marine and terrestrial sources and biomarker analysis can be used to discriminate between the two thereby providing insight into sedimentary and ecological processes we analysed a wide range of lipids from the late miocene 6 6 5 9 ma pissouri section southern cyprus and reconstructed the vegetation supplied to this region by measuring the carbon isotopes of the terrestrial component to identify its geographic source bit branched isoprenoidal tetraether indices reflect changes in the relative abundance of marine vs terrestrial soil organic matter inputs and with the exception of records from the last deglaciation this work is the first application of the bit approach to the reconstruction of orbital impacts on sedimentological processes bit indices show that the organic matter supplied to cyprus changed over the course of each precession cycle and was dominantly terrestrial during insolation maxima when north african run off was enhanced the 13 c values from these intervals are compatible with tropical north african vegetation however the 13 c record indicates that during insolation minima organic material supplied to southern cyprus derives from a more arid source region this is likely to have been aeolian transported organic matter from the anatolian plateau demonstrating that even in mediterranean sedimentary systems influenced by nile run off there is more than one independent precessional organic matter contribution to the sedimentary cyclicity pissouri s organic geochemistry also illustrates a long term trend towards more saline mediterranean conditions during the 600 kyr leading up to the messinian salinity crisis

origin of the plio pleistocene vrica laminites organic geochemical evidence meyers p a 1993 origin of the plio pleistocene vrica laminites organic geochemical evidence mar geol 115 117 127 organic geochemical properties of samples from lower pleistocene laminite layer h at vrica calabria have been examined for evidence of the origin of these dark colored sediments the laminite samples are geochemically distinct from the surrounding gray marly clays they contain less caco 3 and more toc have higher c n ratios and lower 613c values and their hydrocarbon contents indicate larger proportions of land derived organic matter the vrica taminites appear to have originated principally as a consequence of enhanced runoff of land derived organic matter and clastic sediments from nearby land areas during episodes of wetter regional climate freshening of surface waters by the runoff created salinity stratification of the water column diminished availability of oxygen in near bottom waters and improved preservation of organic matter marine productivity was probably also enhanced but not as much as is evident for pelagic sapropels in the eastern mediterranean

modification and complete removal of eastern mediterranean sapropels by postdepositional oxidation sapropels unusually dark organic rich sediment layers whose origin is controversial are widespread in the eastern mediterranean the upper surfaces of these layers appear sharp and show little evidence of bioturbation it has been suggested that postdepositional oxidation may have removed the dark coloration from the upper part of the original layer so that the top of the visible layer now lies somewhat below the original position of the sapropel top such a diagenetic alteration has considerable implications for the interpretation of the sedimentary record where the tops of dark layers are usually correlated with the cessation of sapropel formation geochemical data demonstrate that all visual evidence of a thin example of the most recent eastern mediterranean sapropel has been removed from the sedimentary record by oxidation processes such a process may have thinned all sapropel units by several centimetres the most recent period of sapropel formation probably ended as recently as 5 ka cf cited values between 6 0 and 7 6 ka

trace element indicators of increased primary production and decreased water column ventilation during deposition of latest pliocene sapropels at five locations across the mediterranean sea abstract compositions of productivity and redox sensitive trace metals in two upper pliocene sapropel sequences from western mediterranean odp sites 974 and 975 and eastern mediterranean sites 964 969 and 967 provide information about the conditions leading to sapropel deposition except at site 975 closest to the atlantic ocean all sapropels display elevated element al ratios for ba re cd mo u cr cu v and zn high total organic carbon toc concentrations and ba al ratios point to increased primary productivity during sapropel deposition enrichments of redox sensitive trace elements and elevated re mo ratios indicate water column oxygen depletion during sapropel formation anoxia likely was caused by increased fluxes of organic matter to the seafloor that would have enhanced oxygen demand at depth one of the sapropel sequences investigated in this study insolation cycle 178 contains a zone having low toc low ba al ratios and low trace metal contents these features identify this interval as an interruption of the increased productivity associated with sapropels and of the sub oxic anoxic conditions that are fully developed in the upper half of this sapropel layer significant differences in trace metal enrichments between the eastern and western mediterranean indicate that the eastern basin was a focal point for sapropel initiation in contrast site 975 appears to have been heavily influenced by the atlantic ocean during i cycles 178 and 180 and was not strongly influenced by the paleoceanographic changes affecting the rest of the mediterranean

varve calibrated records of carbonate and organic carbon accumulation over the last 2000 years in the black sea sedimentologic and geochemical studies of box and gravity cores recovered from the black sea during the first leg of a multileg international black sea expedition in 1988 allow reconstruction of the basinwide holocene environmental history of the black sea in the deeper parts of the basin box cores typically recovered a flocculent surface layer fluff laminated coccolith marls of unit i 25 45 cm thick and the upper 5 10 cm of finely laminated dark colored sapropels of unit ii fine grained homogeneous mud turbidites are interbedded with units i and ii over much of the basin but the stratigraphie position of these turbidites differs from site to site the deposition of individual turbidites up to 15 cm thick does not appear to have significantly disturbed underlying laminae sediment trap deployments in the black sea suggest that light and dark laminae couplets represent annual increments of sedimentation i e varves we have therefore constructed a varve chronology for the sequence in order to correlate and date distinctive sedimentation and paleoenvironmental events distinctive groups of laminae in unit i can be correlated across the entire deeper basin a distance of more than 1000 km this implies a remarkable homogeneity in production accumulation and preservation of biogenic material over much of the black sea during deposition of unit i the change from deposition of finely laminated organic carbon rich sapropels unit ii to laminated more calcareous coccolith rich marls unit i is thought to represent the crossing of a salinity threshold for emiliania huxleyi the varve chronology sets this change at about 1 63 ka 1633 100 yr b p but the record of magnetic secular variation measured in several cores produces an age estimate of about 2 0 ka for the base of unit i or about 1 2 times the varve age the average of six calibrated accelerator mass spectrometry radiocarbon ages for the base of unit i is 2 7 ka or about 1 7 times the varve age following the initial change to coccolith dominated sedimentation deposition of sapropel resumed for at least one significant period 1 56 1 25 ka since 1 25 ka cycles of carbonate deposition with quasi decadal periodicities have produced characteristic darker and lighter assemblages of laminae these cycles may have been climatically driven geochemical analyses coupled with the varve ages adopted herein indicate that accumulation rates of carbonate are nearly an order of magnitude higher in unit i averaging 35 45 g m 2 yr 1 than in sapropelic unit ii which contains primarily detrital carbonate the accumulation of lithogenic components in parts of unit i is only 1 5 times the rate in unit ii deepwater organic carbon accumulation rates are somewhat higher in unit i 3 5 4 5 g m 2 yr 1 than in the upper part of unit ii organic carbon accumulation rates in unit i are somewhat antithetic to those of carbonate and on the basis of this and additional constraints placed by pyrolysis and carbon isotopic analyses of organic material it appears that terrestrial organic matter is an important component perhaps 25 of total organic carbon burial in the basin unit i in the western part of the black sea has a higher terrestrial organic component and higher accumulation rates of terrigenous clastic material than unit i in the eastern part this difference between eastern and western black sea is to be expected because of the major rivers that empty into the western black sea from eastern europe ukraine and russia shallow slope sites but still within euxinic bottom waters have lower organic carbon accumulation rates and lower pyrolysis hydrogen indices than deepwater basinal sites suggesting selective resuspension and oxidation of organic matter at basin margins and focusing of organic matter deposition toward the basin center a comparison of the black sea data with those from several open ocean sites with similar water depths showed no significant difference between organic carbon accumulation rates under oxic and anoxic conditions for a given bulk accumulation rate the organic carbon accumulation rates normalized to primary productivity are about the same in both settings

development of photic zone euxinia in the eastern mediterranean basin during deposition of pliocene sapropels abstract carotenoids were analysed in ca 1 cm thick subsamples of three laterally time equivalent sapropels from a west east transect of the eastern mediterranean basin to study euxinic periods during pliocene sapropel formation the amount of intact isorenieratene summed all trans and cis isomers ranged from non detectable at the base and top of a sapropel up to 140 g g sediment in the central parts isorenieratene accumulation rates at the central and western site are remarkably similar and increase sharply to levels of up to 3 0 mg m 2 yr 1 in the central part of the sapropel and then drop to low levels this pattern indicates an expansion of euxinic conditions reaching into the photic zone followed by deepening of the chemocline during deposition of this pliocene sapropel the sapropel from the easternmost site of the basin which contains less organic carbon shows much lower isorenieratene accumulation rates and even absence of isorenieratene in the central part of the sapropel ba al ratios indicate enhanced palaeoproductivity during sapropel formation supporting previously proposed models according to which increased productivity is the driving force for the generation of euxinic conditions

productivity generated annual laminae in mid pliocene sapropels deposited during precessionally forced periods of warmer mediterranean climate abstract paleoproductivity estimates for a sequence of five mid pliocene mediterranean sapropels illustrate the importance of insolation maxima in enhancing organic carbon accumulation well laminated sapropelitic intervals in the northern apennines have been studied by a combination of sedimentological and micropaleontological analysis detailed electron microscope description bulk chemical composition carbon isotopic composition and elemental ratios each sapropel formed during precessional minima lasted 7 5 to 10 kyr which is the same duration calculated for coeval counterparts in odp sites in the eastern mediterranean the organic carbon mass accumulation rates of the studied sapropels show the same values of those calculated in the coeval mediterranean sapropels suggesting that the same productivity conditions were controlling sapropel formation in the whole mediterranean despite the differences in depositional setting and the strong variations in sedimentation rate mat forming diatoms play an important role in increasing the settling velocity allowing rapid sinking of organic matter and preventing bacterial remineralization in the water column the consequent partial oxygen depletion at the seafloor increases preservation which is therefore considered an effect rather than a cause of the organic carbon accumulation

origin and transformation of organic matter in pliocene pleistocene mediterranean sapropels organic geochemical evidence reviewed abstract drilling of deep water post messinian sedimentary sequences by odp legs 160 and 161 in the mediterranean sea has shown that occurrence of organic carbon rich sapropels and sapropel like sediments extends from the levantine basin westward into the alboran basin in the eastern mediterranean sapropel deposition started in the early pliocene whereas in the western basin the onset of sapropel formation occurred later in the early pleistocene precessional cycles are apparently the primary external forcing for sapropel formation nevertheless the pattern of sapropel occurrence suggests that the precessional influence is modulated by the glaciation cycles large differences were observed in the organic carbon contents of sapropels recovered in the eastern and western mediterranean correspondence between organic carbon contents rock eval hydrogen index values and elemental c n ratios indicate that both variations in the production and preservation of marine organic matter have led to the accumulation of high amounts of organic matter in sapropels molecular organic geochemical compositions of sapropels from the eastern mediterranean further confirm that the major fraction of organic matter in sapropels is derived from marine algal sources and has undergone variable oxidation enhanced marine productivity and improved preservation of organic matter is central to sapropel formation accumulation of increased amounts of land derived material at times of sapropel formation is also evidenced supporting the hypothesis of significant periodic freshwater discharges

extension of the astronomically calibrated polarity time scale to the miocene pliocene boundary the early pleistocene to late pliocene astronomically calibrated time scale of shackleton et al 1 and hilgen 2 is extended to the miocene pliocene boundary this is done by correlating the detailed record of caco3 cycles in the trubi and the lower part of the overlying narbone formation rossello composite section sicily to the astronomical record using 1 inferred phase relations between these caco3 cycles and the corresponding orbital cycles of precession and eccentricity and 2 calibration points provided by the previously established astronomical calibration of sapropelitic layers which occur in the topmost part of the caco3 record 2 this correlation allows all small scale caco3 cycles in the rossello composite section to be coded after the correlative precession peak and to be dated astronomically with an accuracy of 1 ky in combination with the available high resolution magnetostratigraphy it further allows the construction of an astronomically calibrated geomagnetic polarity time scale for the major part of the gilbert and gauss chrons this new time scale gives ages for the reversal boundaries of the kaena 3 04 3 11 ma and mammoth 3 22 3 33 ma the gilbert gauss chron boundary 3 58 ma and the reversal boundaries of the cochiti 4 18 4 29 ma nunivak 4 48 4 62 ma sidufjall 4 80 4 89 ma and thvera 4 98 5 23 ma these ages are significantly older than the ages given by conventional time scales age discrepancies gradually increase with increasing age the age of 5 32 ma for the miocene pliocene boundary as defined by the base of the trubi on sicily is almost 0 5 m y 9 5 older than the presently accepted age of 4 86 ma 3 these considerable discrepancies with the conventional time scale can either be explained by an consistent error in the decay constants used in k ar radiometric dating or more likely by diffusional loss of radiogenic argon

active post depositional oxidation of the most recent sapropel s1 in sediments of the eastern mediterranean sea abstract over a wide area of the eastern mediterranean basin two mn rich layers have been observed above the most recent sapropel s1 one immediately above the sapropel top and one a few centimetres closer to the sediment surface different mechanisms have been proposed to explain the occurrence of these two mn peaks either both peaks have a diagenetic origin in which case the upper mn peak is actively forming or the lower peak is actively forming and the upper peak has a different formation mechanism high resolution porewater including a gel sampler used for the first time in marine sediments and solid phase data are now used to demonstrate that the oxidation front is located at the level of the lower mn peak which therefore is presently being formed a barium organic carbon relationship is used to calculate the initial organic carbon profile of the s1 sapropel the palaeoproductivity profiles generated by this method demonstrate that the original sapropel unit was bounded by the upper mn peak this implies that the interval between the two mn peaks where a low organic carbon content is now observed was originally part of the sapropel the initially deposited organic carbon has been oxidised by a progressive downwards moving oxidation front the penetration depth of this oxidation front i e the distance between the two mn peaks is mainly determined by the organic carbon content the sediment accumulation rate and the bioturbation depth the upper mn peak appears to have formed as a result of either mn precipitation upon oxygenation of previously anoxic eastern mediterranean deep water or preservation of a surficial mn peak at the end of the high productivity episode in either case the upper mn peak marks the end of sapropel formation as indicated by the ba profiles this means that formation of the s1 sapropel ceased more recently than is indicated by radiocarbon dating of the visible top of s1

geochemical constraints on pliocene sapropel formation in the eastern mediterranean abstract seventeen eastern mediterranean pliocene sapropels from odp sites 964 966 967 and 969 some of which are coeval have been analysed for their geochemistry the sapropels are characterized by very high organic carbon contents up to 30 which are reported to be the result of both increased productivity and improved preservation although the organic matter in the sapropels is mainly of marine origin the 13 c org values and c n ratios appear terrestrial this is the result of anaerobic organic matter degradation which preferentially removed nitrogen and 13 c rich organic components a comparison with ti al profiles which mimic the precession index and a calculation of organic carbon accumulation rates indicate that sedimentation rates were at most 30 lower or at most 50 higher during sapropel formation thus sapropel formation lasted from between 2000 and 10 000 years at site 964 to between 4500 and 12 000 years at site 967 a synthesis of new data and a comparison with existing models indicates that productivity which increased due to extra nutrients supplied as a result of winter mixing and as a result of enhanced input by the nile was the driving mechanism behind sapropel formation the resulting sapropel formation was simultaneous at different depths but lasted longer in the part of the basin closest to the nile

unraveling north african riverine and eolian contributions to central mediterranean sediments during holocene sapropel s1 formation hydroclimate variability has exerted a fundamental control on the alternating deposition of organic lean marl and organic rich sapropel sediments in the eastern mediterranean sea ems however the exact mechanisms regarding the freshwater sources and related changes are still debated here sr and nd isotopes and high resolution elemental data are used to constrain different riverine and eolian supplies to the central mediterranean over the past 9 8 ka the detrital sediments in core cp10bc taken at the margin of the libyan shelf in the southwestern ionian sea can be described by a three endmember mixing system based on sr and nd isotopic compositions the same systematics can also be deduced from ti and k compositional variability the endmembers comprise saharan dust aegean nile and libyan soil representing the eolian supply from north africa the riverine inputs from the aegean nile areas as well as the riverine and shelf derived fluxes from the libyan tunisian margin respectively for the sapropel s1 period in particular we find important detrital supplies from fossil river wadi systems along the libyan tunisian margin activated by intensified african monsoon precipitation combining the temporal profiles with the consistent variability observed in the 87sr 86sr 1000 sr diagram such libyan contribution has been most prominent during the uppermost period of sapropel s1 in core cp10bc this observation is in agreement with hydroclimate reconstructions of northwestern libya comparison of the sr nd isotope data between core cp10bc and four cores taken along a west east transect throughout the ems shows that this detrital supply originated mainly from western libya tunisia and was transported as far eastward as 25 e while being diluted by an increasing nile contribution

the molecular composition of kerogen in pliocene mediterranean sapropels and associated homogeneous calcareous ooze abstract the organic matter of three time equivalent pliocene sapropels was characterized as being predominantly type ii kerogen using rockeval pyrolysis it is dominated by amorphous organic matter originating mainly from marine organisms as indicated by the relatively high abundances of algaenan and chlorophyll derived pyrolysis products in the curie point pyrolysates of the kerogen of the sapropels however a small amount of terrigenous organic matter was also observed in the form of pollen and spores that most probably yielded the oxygenated aromatic pyrolysis products known to derive from sporopollenin lignin pyrolysis products such as methoxyphenol and catechol 1 2 benzenediol commonly used as unequivocal evidence for a contribution of terrestrial higher plants in the form of woody material to the kerogen were absent from the kerogen pyrolysates no major spatial and temporal differences in the kerogen composition of the three time equivalent sapropels were observed palynological studies revealed that organic matter in the homogeneous intervals below and above the sapropels consisted of pollen spores and amorphous organic matter this was confirmed by curie point pyrolysis gc ms results showing a relatively high abundance of algaenan derived compounds and the presence of oxygenated aromatic pyrolysis products the differences observed between the kerogen pyrolysates of the sapropels and their homogeneous intervals are suggested to be governed primarily by enhanced preservation conditions resulting in increased preservation of marine organic matter in the sapropels

late quaternary changes in mediterranean intermediate water density and formation rate three recently acquired eastern mediterranean cores containing late quaternary sediments display a marked faunal contrast between the holocene and older sapropels it is suggested that the absence of neogloboquadrinids in the holocene sapropel and their abundance in older sapropels reflect differences in food availability related to the extent of development of a deep chlorophyll maximum layer dcm and the intensity of new primary production associated with this layer the depth of such a layer which consists of phytoplankton with a characteristic taxonomic composition is determined by the vertical hydrodynamical structure during deposition of the older sapropels the pycnocline was apparently positioned well above the base of the euphotic layer a situation that favors a pronounced dcm and an associated relatively high rate of new production shallowing of the pycnocline implies a relatively low density of the mediterranean intermediate water miw on the other hand during deposition of the holocene sapropel the pycnocline had apparently vanished due to termination of miw formation

three dimensional 3 d finite strain at the central andean orocline and implications for grain scale shortening in orogens three dimensional 3 d finite strain analyses from across the central andes are used to document the contribution of grain scale strain in quartzites and sandstones to the total shortening budget the results are compared to thermal stratigraphic and strain data from other fold and thrust belts to determine the influence of lithologic strength and deformation temperature on strain accommodation during orogenic evolution in the central andes 3 d best fit ellipsoids are inconsistently oriented relative to structural trends have short axes at high angles to bedding z mean plunge 78 21 and have bedding parallel long axes x mean plunge 6 24 ellipsoid shapes are dominantly oblate x y z indicate low natural octahedral shear strains e s 0 03 0 19 and have axial ratios that range from 1 02 1 0 81 e s 0 19 to 1 02 1 0 97 e s 0 03 highly variable r f data r f 1 0 5 0 fluctuations exceeding 100 indicate detrital grain shapes may overwhelm any measurable tectonic strain fabric recorded by grain geometry the best fit ellipsoids may reflect either weak compaction strain or they may be related to a depositional fabric at a minimum granular strain was insufficient to reset the detrital grain fabric and therefore grain scale strain in quartzites and sandstones is not a significant factor in deformation we suggest that the nonstrained nature of these stiffer lithologies indicates a lack of regional penetrative strain in the central andes like that quantified in similar lithologies in other orogens the regional lack of strain may be due to deformation temperatures

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

on the origin of upper miocene sapropelites a case study from the faneromeni section crete greece for the first time results of an integrated geochemical and micropalaeontological study of upper miocene sapropelites in a land based section in the mediterranean are presented three sapropelites and adjacent homogeneous intervals in the cretan faneromeni section have been investigated in detail the chemical and foraminiferal characteristics were found to be markedly similar to those of plio pleistocene sapropelites as the physiography and climate of the late miocene mediterranean were not fundamentally different from those of today our preferred model for late miocene sapropelite formation is similar to the one recently developed for plio pleistocene sapropelites increased seasonality and freshwater input during northern hemisphere summer insolation maxima triggered high export production and oxygen consumption rates which in combination with a concomitant decrease in deep water formation rate resulted in the observed high organic matter content of the sapropelites

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

geochemical and micropaleontological characterisation of a mediterranean sapropel s5 a case study from core ban89gc09 south of crete several geochemical and micropaleontological proxies were studied in a well developed sapropel s5 from a core collected south of crete to investigate the causes and the mechanisms of its deposition to reconstruct the paleoenvironmental and paleoceanographical conditions at time of its formation and to detect the roles played by productivity and anoxia the geochemical proxies are also used to unravel the sediment provenance and therefore to help tracing water circulation patterns and freshwater sources the multiproxy approach reveals that the sapropel layer has high internal variability and five different depositional phases can be identified four within the visible sapropel layer an increase in temperature and the development of a deep chlorophyll maximum characterise the onset of the sapropel phase 1 with enhanced productivity being favoured by local riverine input not clearly ascribable to nile river freshwater discharge and by the shoaling of the pycnocline nutricline surface water stratification and productivity develop together with strong seafloor dysoxia anoxia phase 2 is characterised by lower stratification slightly lower temperature and or higher seasonal contrast and still high productivity phase 3 records high productivity high temperature and high stratification probably more sustained by the nile input a sudden partial re oxygenation takes place at the end of this phase changing the main features of the sapropel in the fourth phase productivity starts to decrease water stratification seems to be partially broken down and sediment oxygenation increases a transitional phase phase 5 occurs between the end of the visible sapropel and the normal pelagic post sapropel sedimentation where productivity is still high and oxygenation improves compared to the visible sapropel layer the massive occurrence of polysphaeridium zoharyi cyst of a red tide forming dinoflagellate also characterises this phase the geochemical proxies indicate that pre sapropel and post sapropel sediments are quite different from each other and the provenance shifts from a more mixed to a more markedly southern origin of sediments

organic carbon accumulation in bannock basin evaluating the role of productivity in the formation of eastern mediterranean sapropels abstract three sediment cores from bannock basin a hypersaline anoxic basin in the eastern mediterranean have been studied to evaluate the importance of productivity on organic carbon accumulation and sapropel formation in this region organic carbon accumulation rates were determined for two cores from within the anoxic hypersaline zone and for one core from the oxygenated portion of this basin organic carbon accumulation rates are higher by an order of magnitude in the surficial sediments of the anoxic zone due to better preservation an empirically derived preservation factor which allows calculation of paleoproductivity during the deposition of the most recent sapropel si indicates that productivity increased by an order of magnitude during the formation of si we conclude that increased productivity was coupled with a density stratification and a circulation reversal in the eastern mediterranean which together led to sapropel formation

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

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

organic geochemical evidence of late glacial holocene climate instability in the north aegean sea sedimentary molecular biomarker compositions organic carbon and caco3 concentrations and bulk organic 13c and total 15n values document a series of paleoclimatic changes that have affected organic matter production and sedimentation in the north aegean sea from the termination of the latest glacial maximum through the middle holocene continental environmental conditions have been inferred from land plant biomarkers paleoproductivity patterns of diatoms prymnesiophytes dinoflagellates and nannoplankton were discerned from marine derived biomarkers although organic matter is predominantly marine variations in the proportion of marine and land contributions and in its general preservation are evident rapid changes in the eastern mediterranean thermohaline circulation evidently occurred in parallel to sea surface temperature oscillations enhanced deep water ventilation accompanied cold intervals in the late last glacial the younger dryas and during an interruption of deposition of the s1 sapropel probably in response to strengthening of north winds over the region in contrast decreased thermohaline circulation occurred during the warm interval associated with the s1 sapropel during this period increased freshwater inputs diminished ventilation of deep water masses and enhanced organic matter production and preservation intriguing fluctuations in sea surface temperatures and the concentrations of marine and terrestrial biomarkers within the sapropelic layer most prominently in the interruption from 8 2 to 7 8 calibrated radiocarbon conventional kyr bp support the hypothesis that several distinct events of deep water reoxygenation occurred in the north aegean sea during deposition of the s1 sapropel these events reflect centennial excursions to the more common low productivity and well ventilated conditions of the mediterranean that may possibly be related to north atlantic oscillation cycles

the formation of eastern mediterranean sapropels abstract sapropel formation in the eastern mediterranean is explained by an oceanographic approach it is suggested that sapropels are not only a consequence of eustatic sea level changes as earlier proposed by olausson a model which is widely accepted but rather a result of a very sensitive reaction of the eastern mediterranean to any small climatic amelioration present day aeration of the deep eastern mediterranean basin results from circulation of oxygen rich deep water originating mainly in the adriatic assuming present day conditions a climatic amelioration towards more humid and warmer conditions leading to an increase of the water temperature in the adriatic basin by 0 7 c or to a decrease of its salinity by only 0 2 will cause stratification of water masses and enhance sapropel formation

late pleistocene variability of the carbon isotopic composition of organic matter in the eastern mediterranean monitor of changes in carbon sources and atmospheric co2 concentrations the organic carbon isotopic record of the sapropels s1 and s3 s10 and intercalated marl oozes has been determined in a 12 m piston core from the eastern mediterranean the 13corganic values are systematically lighter mean 21 0 0 82 in all sapropels and heavier mean 18 8 1 07 in the marl oozes these differences are not due to variable marine and terrestrial organic matter mixtures because all values are heavier than modern plankton in the mediterranean there is no relationship between the corganic n ratios and the isotopic values and published information on the abundance and distribution of organic biomarkers shows that terrestrial material constitutes a minor fraction of the total organic matter temperature effects on isotope fractionation are also discounted because the change in 13corganic values between glacial and interglacial horizons is in the opposite sense diagenesis which can produce relatively small changes in the carbon isotopic composition of sedimentary organic matter under certain circumstances is unlikely to have caused the observed differences because this mechanism would cause an enrichment in 12c implying that all values were even heavier originally and there is no secular trend in the 13corganic record the observed differences in 13corganic between the two lithologies are probably produced by changes in the isotopic composition and the concentration of dissolved co2 first freshwater flooding during the formation of the sapropels caused the isotopic composition of the dissolved inorganic carbon in the surface waters of the mediterranean to become lighter because of the 13c deficiency in fresh waters hence photosynthesis would have produced isotopically lighter organic material second changes in atmospheric pco2 between glacial and interglacial periods as shown by the vostok ice core caused marked changes in the concentration of free dissolved co2 in the mixed layer lower values during glacial maxima caused a smaller fractionation of the carbon isotopes by phytoplankton whereas levels were less limiting during the interglacials concentrations of dissolved co2 could also have been much higher during the deposition of the sapropels because of the supply of regenerated co2 to the mixed layer by upwelling and this could have further lightened the 13corganic values in the sapropels themselves carbon isotope records may provide an alternative method for estimating atmospheric pco2 levels over longer time periods than can be obtained from ice cores

middle miocene langhian sapropel formation in the easternmost mediterranean deep water basin evidence from northern cyprus abstract mid miocene langhian 15 4 ma sapropels formed within the easternmost mediterranean basin now uplifted in northern cyprus these sapropels represent the oldest known sapropels in a predominantly marl succession six well developed sapropels were studied strontium isotope dating of twelve samples gave a preferred age of 15 4 ma langhian i e during the final phases of the middle miocene climatic optimum mco the age of the best preserved nannofossil assemblage langhian is close to the strontium ages the langhian strontium ages are preferred over an alternative early serravallian age for less well preserved nannofossil assemblages total organic carbon contents in the sapropels reach maximum values of 3 9 wt relative to the host marls the sapropels show enrichments in terrigenous derived minerals and related major and trace elements sedimentological evidence indicates that the terrigenous sediments were eroded from the northern borderlands of the deep water basin under warm humid conditions high fresh water run off from surrounding landmasses is likely to have promoted a low salinity lid to the eastern mediterranean deep water basin this in turn would have restricted deep water ventilation and promoted widespread anoxia exceptionally high concentrations of chalcophile elements e g cu ni and zn are consistent with anoxic conditions abundant nutrient rich fresh water input is also likely to have stimulated siliceous productivity although any siliceous microfossils did not survive diagenesis a significant role for diagenesis in sapropel formation is indicated by the mobilisation of ba from sapropels to marl directly beneath orbitally induced dry wet oscillation the mechanism invoked to explain the pliocene to holocene sapropels apparently was already in place during the latest stages of the mco when the langhian sapropels accumulated these sapropels accumulated immediately after the middle miocene closure of the southern neotethys when the eastern mediterranean sea apparently became more sensitive to orbital cyclicity the development of a semi enclosed deep water basin was therefore a prerequisite for sapropel formation

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

the occurrence and significance of pleistocene and upper pliocene sapropels in the tyrrhenian sea numerous sapropels and sapropelic strata from upper pliocene and pleistocene hemipelagic sediments of the tyrrhenian sea show that intermittent anoxia possibly related to strongly increased biological productivity was not restricted to the eastern mediterranean basins and may be a basin wide result of late pliocene pleistocene climatic variability even though the sapropel assemblage of the tyrrhenian sea clearly originates from multiple processes such as deposition under anoxic conditions or during spikes in surface water productivity and lateral transport of organic rich suspensates many pelagic sapropels have been recognized stratigraphic ages calculated for the organic rich strata recovered during odp leg 107 indicate that the frequency of sapropel formation increased from the lowermost pleistocene to the base of the jaramillo magnetic event coinciding with a period when stable isotope records of planktonic foraminifera indicate the onset of climatic cooling in the mediterranean a second very pronounced peak in sapropel formation occurred in the middle to late pleistocene 0 73 0 26 ma formainifers studied in three high resolution sample sets suggest that changes in surface water temperature may have been responsible for establishing anoxic conditions while salinity differences were not noted in the faunal assemblage however comparison of sapropel occurrence at site 653 with the oxygen isotopic record of planktonic foraminifers established by thunell et al proc odp sci results 107 1990 indicates that sapropel occurrences coincide with negative 18o excursions in planktonic foraminifers in thirteen of eighteen sapropels recognized in hole 653a a variant of the meltwater hypothesis accepted for sapropel formation in the late pleistocene eastern mediterranean may thus be the cause of several anoxic events in the tyrrhenian as well model calculations indicate that the amount of oxygen advection from western mediterranean deep water exerts the dominant control on the oxygen content in deep water of the tyrrhenian sea inhibition of deep water formation in the northern adriatic and the balearic basin by increased meltwater discharge and changing storm patterns during climatic amelioration may thus be responsible for sapropel formation in the tyrrhenian sea

north african paleodrainage discharges to the central mediterranean during the last 18 000 years a multiproxy characterization using elemental geochemistry clay mineralogy grain size end member modeling and planktonic foraminiferal 18o we characterize the provenance of central mediterranean sediments over the past 18 ka the provenance is dust dominated before and after the african humid period ahp by contrast during the ahp 11 5 ka largely concurrent with organic rich sapropel s1 formation it is predominantly riverine from north african sources such fluvial supply is suggested to come from paleodrainage networks that were reactivated by intensified monsoon precipitation during the ahp the supply is characterized by high mg al and smectite contents and has been accompanied by considerable freshwater influx as indicated by the enhanced grain size and lighter foraminiferal 18o the clay mineral assemblages in our core and in nearby cores correspond with a provenance from the libyan tunisian margin mainly via the paleo river irharhar the inferred fluvial discharge is strongest during the late ahp 8 5 5 ka coinciding with reported enhanced fluvial dynamics and wettest conditions over western libya and tunisia algeria this period is not only synchronous with the largest extension of open water bodies in north africa and lowest saharan dust inputs but also consistent with precipitation records of the west african monsoon moreover our records show a remarkable correspondence with that of a paleodrainage system towards the atlantic west african margin inferring a common headwater region in the central saharan mountains and a similar climate mechanism taken together we suggest a dominant control of north african humid surfaces on the paleodrainage delivery modulated by groundwater level in response to the insolation driven west african monsoon precipitation

geochemistry of eastern mediterranean sediments primary sediment composition and diagenetic alterations abstract two cores recovered in the eastern mediterranean were analysed for major minor and trace elements the primary chemical composition of the sediment is different at each location probably because the lithological sources and the relative biogenic contributions differ carbonates are important for the concentration of ca mg and sr whereas aluminosilicates determine the concentration of si al k li y and be and to a lesser extent that of fe cr ti mg zn and zr in sapropels organic carbon and sulphur seem to be closely related bromine mo p fe v cu zn co ni and cr are closely associated with organic and sulphidic compounds the concentration versus depth profile for organic carbon in two sapropels points to a rapid establishment of conditions that gave rise to sapropel formation followed by a gradual transition back to normal conditions the primary composition is overprinted by diagenetic processes sulphate reducing conditions occurred during and just after sapropel deposition a progressive oxidation front mechanism which became active after sapropel deposition is responsible for additional major geochemical changes this diagenetic phenomenon has strong implications for the chemistry of fe mn ni co zn cu cr v u as and sb

late quaternary mediterranean sapropels iii assessment of source of input and palaeotemperature as derived from biological markers abstract sources of input contributing to the organic matter of four different mediterranean sapropels s1 s5 s6 s7 are inferred from the relative distributions of terrigenous and marine biological markers in these quaternary deposits the relative terrigenous contribution does not vary significantly within the marine contribution there is a significant compositional variation a contribution from dinoflagellates is relatively important in the s1 sapropel whereas sapropels s6 and s7 are characterized by a relatively large contribution from prymnesiophyte algae and planktonic cyanobacteria the abundance of diatoms in sapropel s5 as deduced from microscopic observations is probably reflected by a high concentration of loliolide variations in sea surface water temperatures can be deduced from the relative abundance of di and triunsaturated c37 ketones uk37 index and from the relative abundance of esterified 27 nor 24 methylcholesta 5 22e dien 3 ol and cholesta 5 22e dien 3 ol sti index these two molecular temperature indices are consistent with the 18o record and with the pollen record of the sapropels investigated

mediterranean functioning and sapropel formation respective influences of climate and hydrological changes in the atlantic and the mediterranean abstract during ocean drilling program odp legs 160 and 161 sapropels were recovered both in the western and eastern mediterranean this obliges to a reassessment of the previous studies focused on sapropels from only the eastern mediterranean and to consider the changes which occurred in the mediterranean climate but also in the water characteristics both in the atlantic and in the western mediterranean in the north atlantic the position of the polar front which migrated southwards during glacial times and the melting of northern ice caps during interglacial periods together with the convection in the labrador and norwegian seas appear essential to control the salinities of the waters facing the strait of gibraltar the salinities of the surface and intermediate layers constitute the first driving force of the mediterranean dynamics the second driving force being the mediterranean climate the stagnation of deep waters leading to sapropel deposition in the western mediterranean may be explained by a drastic weakening of the density difference between mediterranean outflow and atlantic intermediate waters facing the strait of gibraltar this weakening was induced primarily by the salinity decrease of atlantic surface water and secondly by a rather high salinity in the atlantic intermediate layer rather than by a drastic deterioration of the mediterranean climate this scenario probably concerns most of the sapropel events and it may be used for the knowledge of atlantic and mediterranean functioning over climatic changes

redistribution and geochemical behaviour of redox sensitive elements around s1 the most recent eastern mediterranean sapropel the youngest eastern mediterranean sapropel s1 is generally believed to have formed 7 9 14c ky b p the distribution of redox sensitive elements above in and below the sharply defined organic rich unit reveal that s 1 has already suffered heavy diagenetic alteration its present thickness based on its dark colour is only a fraction of its original thickness in one core visual evidence of s1 with an inferred initial thickness of 6 cm has been destroyed and a similar thickness appears to have been lost from the tops of another two examples this is caused by oxidation of the upper reaches of s 1 by a progressive oxidation front which commenced 5 2 5 4 14c ky ago and still appears to be active in the three cores studied diagenetic relocation of many redox sensitive elements has occurred most elements expected to be enriched in sapropels or sulphide rich sediments already have maximum concentrations above or below rather than in the present s 1 layers similarities are observed in the geochemical behaviour of as fe and p of co cu mn ni and zn and of cd mo sb ti u and v the behaviour of ba is distinctive and its immobility as barite makes it an indicator for palaeoproductivity and the original high s1 corg content the elements se and i exhibit particularly large sharp concentration peaks and together are proposed as useful indicators of the present boundary between oxic and post oxic conditions

water column dynamics during the last interglacial anoxic event in the mediterranean sapropel s5 1 marine organic rich sediments are important for long term carbon sequestration and as a source of fossil hydrocarbons but the processes underlying their formation remain elusive we present a multiproxy analysis of a relatively recent well preserved mediterranean organic rich deposit known as sapropel s5 which formed 124 119 thousand years ago ka b p where b p references year 1950 combining planktonic foraminiferal abundance records with stable isotope and organic biomarker data we reconcile the apparently contradicting coexistence of deep dwelling foraminiferal faunas with green sulphur bacteria that indicate photic zone euxinia s5 started with a rapid freshwater induced increase of density stratification that inhibited vertical mixing and deepwater ventilation through the first 900 years anoxic to euxinic deepwater conditions developed and extended up to roughly 200 m water depth then followed a 4100 year period of variability in the depth intensity of winter mixing with a roughly 1400 year periodicity coincident with fluctuations in water column stability s5 terminated with a marked decrease in density stratification and consequently renewed convective overturn

combined organic and inorganic geochemical reconstruction of paleodepositional conditions of a pliocene sapropel from the eastern mediterranean sea layers of organic carbon rich sapropels in the sediment record of the mediterranean sea give evidence of repetitive changes in regional plio pleistocene climate results from biomarker molecule and major and trace element analyses of closely spaced samples are used to reconstruct the conditions leading to deposition of a pliocene sapropel at ocean drilling program odp site 969 on the mediterranean ridge organic carbon concentrations increase from 0 2 outside the sapropel and peak to more than 30 within it major and trace elemental composition and biomarker derived parameters indicate elevated productivity depletion of water column dissolved oxygen content and changes in sediment provenance in response to climatic changes budgets of rhenium thallium and other trace metals indicate that deep water exchange between the mediterranean subbasins and the atlantic ocean was not completely interrupted during sapropel formation enrichment factors of redox sensitive and sulfide forming trace metals as well as the presence of isorenieratene derivatives and high stanol sterol ratios point to an extended zone of anoxic water masses depth profiles of biomarker compositions sterols long chain alkenones alkandiols and ketols fatty acids indicate great floral diversity during deposition of a single sapropel and highlight the sensitive response of the marine community to variable environmental conditions changes in water mass circulation and eolian transport can be reconstructed by use of both lithogenic elements and average chain lengths of n alkanes acl index

organic matter and trace element rich sapropels and black shales a geochemical comparison a distinct pliocene eastern mediterranean sapropel i 282 recovered from three ocean drilling program odp leg 160 sites has been investigated for its organic and inorganic composition this sapropel is characterized by high organic carbon corg and trace element contents and the presence of isorenieratene derivatives the latter suggests that the base of the photic zone was sulphidic during formation of the sapropel combined with evidence of bottom water anoxia preservation of laminae high redox sensitive trace element contents and the abundance and isotopic composition of pyrite this leads to the tentative conclusion that almost the entire water column may have been anoxic this anoxia resulted from high productivity and not from stagnation because an approximation of the trace element budget during sapropel formation shows that water exchange with the western mediterranean is needed entire water column anoxia has been suggested earlier for several black shales with regard to the depositional environment and the corg content however only the cenomanian turonian boundary event ctbe black shales appear to be comparable to this sapropel the proposed trace element removal mechanism of scavenging and co precipitation in an anoxic water column is thought to be similar for both types of deposits the ultimate trace element source for the sapropel however is seawater whereas it is hydrothermal and fluvial input for ctbe black shales because they have a larger temporal and spatial distribution nonetheless the corg rich eastern mediterranean pliocene sapropel discussed here may be considered to be a younger analogue of ctbe black shales

transfer functions to reconstruct ocean palaeoproductivity a comparison oceanic plankton export productivity contributes to the control of glacial to interglacial changes in atmospheric co2 concentration the extent of this contribution may be deciphered from global reconstructions of palaeoproductivity we quantitatively estimate palaeoproductivity over the last 350 000 years in the eastern equatorial atlantic using equations based on foraminiferal assemblages and marine organic carbon accumulation rates and make qualitative estimates using diatom and radiolarian accumulation rates these proxydata are calibrated to data on modern primary production

cyclic variations in the chemical composition of eastern mediterranean pliocene sediments a key for understanding sapropel formation abstract two pliocene mediterranean sediment cores from ocean drilling program odp leg 160 sites 964 pisano plateau ionian basin and 967 lower northern slope of eratosthenes seamount south of cyprus have been analyzed for major and minor elements si ti al fe mg ca k ba cr ni v zn zr by x ray fluorescence analysis at a depth resolution of 3 to 4 cm a total of 430 samples core 964c 9h comprises five sapropels with up to 9 7 total organic carbon toc one 2 5 m thick turbidite and a 50 cm segment of a second turbidite whereas core 967b 9h contains eight sapropels with toc contents of up to 6 7 cyclic variations in carbonate content and detrital matter composition are evident at both sites at site 964 pisano plateau terrigenous detrital matter chemistry reflects periods of stronger saharan dust input higher si al and zr al ratios alternating with fluvial input from the northern borderlands higher mg al ratios cyclicity is not well expressed at this location because turbidites and winnowing occur site 967 eratosthenes seamount sediments are strongly influenced by discharge from the nile river during humid periods low k al and mg al ratios at site 967 sapropels occur only during periods of enhanced nile discharge with correspondingly lower si al ti al mg al k al and zr al ratios accumulation rates of carbonate and terrigenous detrital matter were 30 lower during such episodes because of the reduction in eolian input and carbonate production and or carbonate dissolution periodical ba enrichments which are not only seen in the sapropels but in every k al minimum document the association of enhanced bioproductivity and sapropel formation as calculated from excess ba concentrations productivity increased by up to a factor of five during intervals of intensified nile runoff fluviatile discharge seems to be responsible for an enhanced input of nutrients and suspended matter containing low mg al and k al ratios based on organic carbon concentrations episodes of sapropel formation lasted at least from 1000 to 4000 years at site 964 and from 2000 to 6000 years at site 967 periods of enhanced bio productivity as defined by ba enrichments lasted from 8000 to 12 000 years at site 967 episodes of high river discharge and corresponding nutrient input as well as conditions of sapropel formation seem to have lasted longer in the eastern part of the basin site 967 than at the pisano plateau site 964

diagenetic pyritisation under eastern mediterranean sapropels caused by downward sulphide diffusion recurrent organic rich layers sapropels in eastern mediterranean sediments are enriched in corg fe and s sulphur and fe are enriched in a zone immediately below the sapropels whereas corg is not 34s values of bulk sediments and simple mass balance calculations indicate that so42 reduction has taken place in an open system with all hs formed at or close to the sediment surface formation of pyrite in the sapropel was fe limited and consequently excess hs was able to migrate downwards downward sulphidisation this resulted in the formation of pyrite below the sapropel by reaction of this hs with solid phase ferric iron and fe2 diffusing upwards from underlying sediments the fe2 source probably includes fe hydr oxide layers formed at former oxidation fronts above previously deposited and buried sapropels this downward sulphidisation mechanism allows accumulation of twice as much s in alternating organic rich anoxic organic poor suboxic sediments compared to what is preserved in organic rich anoxic sediments

paleomagnetic and geochemical record from cores from the sea of marmara turkey age constraints and implications of sapropelic deposition on early diagenesis abstract we present results of a multi proxy analysis of two sediment cores from the marmara sea the cores were analyzed using paleomagnetic and geochemical measurements two sapropels are documented in the last 11 kyr and are recorded in several locations across the marmara sea these two sapropels have contrasting magnetic properties the magnetic record is affected by intense early diagenesis the most recent upper sapropelic layer has low remanence and susceptibility values a record of paleomagnetic inclinations could still be isolated above the diagenesis front and is compared with secular variation models the lower sapropel is identified in the deep part of the oldest studied core klg07 and has distinct magnetic properties characterized by high remanence and susceptibility values using the magnetic properties it is possible to constrain bottom water ventilation and reconnection episodes between the marmara sea and the black sea following the sea level rise during the last glacial to inter glacial transition

efficiency of heavy liquid separation to concentrate magnetic particles summary low temperature rock magnetic measurements have distinct diagnostic value however in most bulk marine sediments the concentration of ferrimagnetic and antiferromagnetic minerals is extremely low so even sensitive instrumentation often responds to the paramagnetic contribution of the silicate matrix in the residual field of the magnetometer analysis of magnetic extracts is usually performed to solve the problems raised by low magnetic concentrations additionally magnetic extracts can be used for several other analyses for example electron microscopy or x ray diffraction the magnetic extraction technique is generally sufficient for sediments dominated by magnetite in this study however we show that high coercivity components are rather underrepresented in magnetic extracts of sediments with a more complex magnetic mineralogy we test heavy liquid separation using hydrophilic sodium polytungstenate solution na6 h2w12o40 to demonstrate the efficiencies of both concentration techniques low temperature cycling of zero field cooled field cooled and saturation isothermal remanent magnetization acquired at room temperature was performed on dry bulk sediments magnetic extracts and heavy liquid separates of clay rich pelagic sediments originating from the equatorial atlantic the results of the thermomagnetic measurements clarify that magnetic extraction favours components with high spontaneous magnetization such as magnetite and titanomagnetite the heavy liquid separation is unbiased with respect to high and low coercive minerals thus it represents the entire magnetic assemblage

influence of water column anoxia on the burial and preservation of carbon and phosphorus in marine shales abstract organic p and organic c concentrations were measured in several well characterized phanerozoic marine shale sequences with the primary focus being the camp run member of the devonian mississippian new albany shale sequences were selected with close spatial association of bioturbated and laminated sediments which reflect deposition from oxic and anoxic waters respectively average organic c p mole ratios calculated from the data are 150 for bioturbated shales and 3900 for the laminated shales of the new albany differences in the extent and mechanisms of early diagenesis related to the oxygenation of waters at the sediment water interface can account for the c p ratios of buried organic matter low c p ratios of bioturbated sediments are attributed to 1 1 the increased ability of bacteria to store p in well oxygenated environments which leads to the production of low c p ratio bacterial biomass and 2 2 the extensive oxidation of sedimentary organic matter resulting in the formation of residual organic phases with low c p ratios high organic c p ratios of laminated sediments are explained by a combination of 1 1 the limited ability of bacteria to store p under anoxic conditions 2 2 extensive p regeneration from sedimentary organic matter 3 3 enhanced c preservation relative to the bioturbated shales it is also shown that relative to organic c laminated shales are not as effective a p sink as are bioturbated shales this provides a mechanism in anoxic environments for burying large quantities of organic matter without simultaneously sequestering the p needed to sustain further productivity

distribution of exchangeable fixed organic and total nitrogen in interbedded turbiditic pelagic sediments of the madeira abyssal plain eastern north atlantic abstract nitrogen compounds in the interbedded turbiditic pelagic sediments of the madeira abyssal plain from hereon map have been divided in separate extracted fractions such as exchangeable nitrogen nex fixed nitrogen nfix and organic nitrogen norg nex is found to be directly proportional to the amount of organic matter corg in the sediment and is not related to the amount of ammonium in the porewater only at a relatively low corg content is the nex determined by the mineralogy of the sediment the norg as determined from norg ntot nfix nex is strongly related with corg the nfix content and the n fix al ratio for organic rich sediments are high compared with other sediments and have not changed upon post depositional oxidation of the organic matter post depositional oxidation of organic matter through oxygen does lead to a decrease in the c n ratio of the remaining organic matter in the organic rich turbidites the c n ratio calculated for the organic matter that has been decomposed through oxygen is similar to that calculated through stoichiometric modelling for decomposition under reducing circumstances c n ratios of 17 and 18 respectively this implies that for the sediments of the map the c n ratio is identical for organic matter decomposed under oxygenated and under reducing conditions

black shale deposition on the northwest african shelf during the cenomanian turonian oceanic anoxic event climate coupling and global organic carbon burial high resolution geochemical records from a depth transect through the cenomanian turonian c t tarfaya basin northwest african shelf reveal high amplitude fluctuations in accumulation rates of organic carbon oc redox sensitive and sulphide forming trace metals and biomarkers indicative of photic zone euxinia these fluctuations are in general coeval and thus imply a strong relationship of oc burial and water column redox conditions the pacing and regularity of the records and the absence of a prominent continental signature suggest a dynamic depositional setting linked to orbital and higher frequency forcing determining the dominant frequency depends on the definition of the most pronounced oceanic anoxic event oae2 and its duration we propose that eccentricity is the main forcing factor at tarfaya and controlled fluctuations in wind driven upwelling of nutrient rich oxygen depleted intermediate waters from the adjacent atlantic and the periodic development of photic zone and bottom water euxinia on the mid cretaceous northwest african shelf accumulation records clearly identify the basin center as the primary site of sediment deposition with highest temporal variability and an up to six fold increase in oc burial from similar to2 g m 2 yr prior to the oae2 to similar to12 g m 2 yr during the oae2 photic zone and bottom water euxinia alternated with periods of greater oxygenation of the water column in response to climate forcing mass balance calculations imply that similar to2 of the overall global excess oc burial associated with the oae2 was deposited in the tarfaya basin an area that represented only similar to0 05 of the total global c t ocean floor in fact the lateral extent of similar black shales along the african continental margin indicates that this part of the ocean contributed significantly to the global increase in organic carbon burial during the oae2

sulphidic mediterranean surface waters during pliocene sapropel formation sapropels organic matter rich layers are common in neogene sediments of the eastern mediterranean sea the formation of these layers has been attributed to climate related increases in organic matter production1 2 3 and increased organic matter preservation due to oxygen depletion in more stagnant bottom waters2 3 here we report that eastern mediterranean pliocene sapropels4 contain molecular fossils of a compound isorenieratene known to be synthesized by photosynthetic green sulphur bacteria suggesting that sulphidic euxinic and therefore anoxic conditions prevailed in the photic zone of the water column these sapropels also have a high trace metal content which is probably due to the efficient scavenging of these metals by precipitating sulphides in a euxinic water column the abundance and sulphur isotope composition of pyrite are consistent with iron sulphide formation in the water column we conclude that basin wide water column euxinia occurred over substantial periods during pliocene sapropel formation in the eastern mediterranean sea and that the ultimate degradation of the increased organic matter production was strongly influential in generating and sustaining the euxinic conditions

recent sapropel formation in the eastern mediterranean during the 1983 expedition of the rv tyro in the eastern mediterranean a combined programme of seismological micropalaeontological and geochemical research was performed the geochemical research focused mainly on the interstitial water and the chemical composition and origin of sapropels for this purpose box cores piston cores and bottom water samples were collected we report here that some of these cores showed clear evidence of long term stagnant bottom water conditions in a small basin south of crete for which we propose the name tyro basin 1 the bottom water is strongly anoxic whereas the sediment down to at least 400 cm is sapropel to sapropelic as salt concentrations in the bottom water are eight times higher than in normal seawater the anoxic conditions in this basin are probably due indirectly to dissolution of salt from a nearby diapir

pliocene holocene evolution of depositional conditions in the eastern mediterranean role of anoxia vs productivity at time of sapropel deposition a multiproxy geochemical study of nine sapropel layers from odp hole 964a odp leg 160 in the eastern mediterranean spanning the pliocene holocene time interval provides new insights into the evolution of sapropel deposition paleoenvironmental proxies were used for reconstruction of productivity ba derived from marine barite oxygen conditions trace metal ratios and sedimentary regime clay minerals detrital elements these proxies reveal a significant increase in river runoff relative to decreasing aeolian input during sapropel deposition over the whole time interval ba excess supports the argument that a significant increase in export productivity is the main triggering mechanism for sapropel deposition although preservation also played an important role furthermore major differences exist in depositional conditions including both oxygenation and productivity since the pliocene productivity fluctuated substantially and was higher during the pliocene and pleistocene than during the holocene at the same time decreasing oxygen availability parallels the enhanced productivity dysoxic to anoxic conditions appear to coincide with marine productivity maxima thus suggesting that oxygen depletion may be linked to greater consumption rather than restricted circulation this correspondence supports the hypothesis that productivity fluctuations resulting from climate oscillations were the main cause of enhanced organic matter contents and also a main controlling factor for reduced oxygen availability

a novel selective extraction of barite and its application to eastern mediterranean sediments abstract a sequential extraction method basex was developed to determine the different ba fractions in sediments calibration of basex with pure barite and a home made mixed mineral standard showed that barite is separated from all other major ba containing mineral phases such as clay minerals and fe and mn oxides this method permits the direct determination of sedimentary barite content and of the ba al ratio of clay and is therefore a useful tool in palaeoclimatic studies application of basex to eastern mediterranean sediments including sapropel s1 revealed that the enrichment in ba concentrations observed in this sapropel consists predominantly of barite the relationship of barite ba with organic carbon in sapropel s1 sediments appears to be independent of water depth of organic matter fluxes and of the sedimentation rate for cores ranging from 2150 to 3300 m water depth apparently organic carbon remineralisation has been virtually absent in the water column deeper than 2150 m this might have been caused by suboxic to anoxic conditions present in the deep eastern mediterranean basin during the formation of sapropel s1 because of the constant relationship between barite and organic carbon in sapropelic sediments we suggest that the barite content can be used to quantify the initial organic carbon content of the sediment in the oxidised sapropel interval

trace elemental derived paleoceanographic and paleoclimatic conditions for pleistocene eastern mediterranean sapropels abstract eastern mediterranean sediments are characterized by cyclic deposition of organic rich sediments known as sapropels enhanced primary productivity combined with bottom water oxygen depletion are thought to be the main drivers for sapropel deposition we selected sapropel layers from a suite of odp leg 160 cores and applied a set of geochemical proxies to determine paleo productivity variations redox conditions of the water column during deposition and provenance of detrital material high sedimentary ba al and corg contents indicate enhanced primary production whereas the sedimentary la lu ratio points to an enhanced contribution from a north african riverine source during sapropel formation these features are especially pronounced on sapropels s5 and s7 deposited during a particularly warm climatic interval this indicates a more intense north african drainage weathering and consequently run off for those sapropels that have the most enhanced expression of productivity too correspondingly the latter has also resulted in bottom water redox conditions that have been more severe during these sapropels than during others deepwater formation from adriatic and aegean areas thought to be mainly controlled by sustained cooling of preconditioned surface waters triggers the onset of bottomwater ventilation thus sapropel duration our data therefore suggest that the intensity of sapropel formation is determined by the north african monsoonal system whereas their duration is directed by northern borderlands climatic conditions