sulfur isotope partitioning during experimental formation of pyrite via the polysulfide and hydrogen sulfide pathways implications for the interpretation of sedimentary and hydrothermal pyrite isotope records we show that the sulfur isotopic composition of sedimentary and hydrothermal pyrite is a good approximation of the average sulfur isotopic composition of the dissolved sulfide sources from which the pyrite formed consequently pyrite sulfur isotope systematics normally provide little evidence of the pyrite forming mechanism in most natural systems stable sulfur isotope partitioning during pyrite fes2 synthesis via the polysulfide and h2s pathways was investigated between 80 and 120 c iron monosulfide fes was reacted with hydrogen sulfide h2s or tetrasulfide s42 in aqueous solution under strictly anoxic conditions the results provide independent confirmation of the hydrogen sulfide and polysulfide mechanisms the measured isotopic composition of the synthesized pyrite is compared with 1 isotopic mixing models of the reactant reservoirs and 2 predictions based on the suggested mechanisms for the hydrogen sulfide and polysulfide pathways for pyrite formation the isotopic composition of the pyrite product is consistent with the result predicted from the reaction mechanisms pyrite produced via the h2s pathway has a composition reflecting isotopic contributions from both fes and h2s reservoirs pyrite formed via the polysulfide pathway inherits an isotopic composition dominated by the polysulfide reservoir in both cases solubility driven isotope exchange between fes and aqueous s species contribute to the final pyrite composition we show that published experimental sulfur isotope data for pyrite formation which apparently support conflicting pyrite forming pathways are consistent with pyritization via the polysulfide and h2s pathways formation rates of natural pyrite however may be too slow compared to solubility exchange for the influence of the reaction pathway on the isotopic composition to be significant

trace metal signatures of eastern mediterranean sapropels abstract sapropel samples of pliocene to pleistocene age recovered during odp leg 160 from sites 964 ionian basin 969 mediterranean ridge 966 967 top and northern slope of the eratosthenes seamount south of cyprus and 968 cyprus margin were analysed for major and trace elements eastern mediterranean sapropels are characterized by high organic carbon and sulphur contents and by significant enrichments in several redox sensitive and or sulphide forming trace metals bi cd co cr cu mo ni re sb tl u v enrichment factors relative to average shale are comparable to those found in ctbe black shales the re content is extremely high in the sapropels studied with maximum values up to 1000 ng g re mo ratios averaging 2 7 10 3 are close to the seawater value high trace metal enrichments and re mo ratios close to the seawater value point to an anoxic water column during sapropel formation additionally enhanced ba concentrations in the sapropels support the assumption that bioproductivity was also high during these episodes trace metal signatures of sapropels originating from different drill sites on a transect across the eastern mediterranean are not only influenced by water depth but also by their location in the eastern mediterranean metal enrichments seem to be higher at the western sites compared with the eastern sites this probably reflects a change in the circulation pattern during periods of sapropel formation pliocene sapropels exhibit elevated trace metal contents in comparison with pleistocene examples therefore different palaeoceanographic conditions may have developed during the pleistocene compared with the pliocene altering palaeoceanography was probably controlled by climatic change which may be related to the onset of glaciation of the northern hemisphere decreasing summer precipitation throughout the late pliocene and the pleistocene may also have influenced sapropel deposition

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

pyritization processes and greigite formation in the advancing sulfidization front in the upper pleistocene sediments of the black sea pyritization in late pleistocene sediments of the black sea is driven by sulfide formed during anaerobic methane oxidation a sulfidization front is formed by the opposing gradients of sulfide and dissolved iron the sulfidization processes are controlled by the diffusion flux of sulfide from above and by the solid reactive iron content two processes of diffusion limited pyrite formation were identified the first process includes pyrite precipitation with the accumulation of iron sulfide precursors with the average chemical composition of fesn n 1 10 1 29 including greigite elemental sulfur and polysulfides formed from h2s by a reductive dissolution of fe iii containing minerals serve as intermediates to convert iron sulfides into pyrite in the second process a direct pyrite precipitation occurs through prolonged exposure of iron containing minerals to dissolved sulfide methane driven sulfate reduction at depth causes a progressive formation of pyrite with a 34s of up to 15 0 the s isotopic composition of fes2 evolves due to contributions of different sulfur pools formed at different times steady state model calculations for the advancement of the sulfidization front showed that the process started at the pleistocene holocene transition between 6360 and 11 600 yr bp our study highlights the importance of anaerobic methane oxidation in generating and maintaining s enriched layers in marine sediments and has paleoenvironmental implications

anaerobic methane oxidation and a deep h2s sink generate isotopically heavy sulfides in black sea sediments the main terminal processes of organic matter mineralization in anoxic black sea sediments underlying the sulfidic water column are sulfate reduction in the upper 2 4 m and methanogenesis below the sulfate zone the modern marine deposits comprise a ca 1 m deep layer of coccolith ooze and underlying sapropel below which sea water ions penetrate deep down into the limnic pleistocene deposits from 9000 years bp sulfate reduction rates have a subsurface maximum at the so42 ch4 transition where h2s reaches maximum concentration because of an excess of reactive iron in the deep limnic deposits most of the methane derived h2s is drawn downward to a sulfidization front where it reacts with fe iii and with fe2 diffusing up from below the h2s fe2 transition is marked by a black band of amorphous iron sulfide above which distinct horizons of greigite and pyrite formation occur the pore water gradients respond dynamically to environmental changes in the black sea with relatively short time constants of ca 500 yr for so42 and 10 yr for h2s whereas the fes in the black band has taken ca 3000 yr to accumulate the dual diffusion interfaces of so42 ch4 and h2s fe2 cause the trapping of isotopically heavy iron sulfide with 34s 15 to 33 at the sulfidization front a diffusion model for sulfur isotopes shows that the so42 diffusing downward into the so42 ch4 transition has an isotopic composition of 19 close to the 23 of h2s diffusing upward these isotopic compositions are however very different from the porewater so42 43 and h2s 15 at the same depth the model explains how methane driven sulfate reduction combined with a deep h2s sink leads to isotopically heavy pyrite in a sediment open to diffusion these results have general implications for the marine sulfur cycle and for the interpretation of sulfur isotopic data in modern sediments and in sedimentary rocks throughout earth s history

control of sulfate pore water profiles by sedimentary events and the significance of anaerobic oxidation of methane for the burial of sulfur in marine sediments abstract gravity driven mass flow deposits proven by sedimentary and digital echosounder data are indicative for prevailing dynamic sedimentary conditions along the continental margin of the western argentine basin in this study we present geochemical data from a total of 23 gravity cores pore water so 4 is generally depleted within a few meters below the sediment surface by anaerobic oxidation of methane aom the different shapes of so 4 profiles concave kink and s type can be consistently explained by sedimentary slides possibly in combination with changes in the ch 4 flux from below thus mostly representing transient pore water conditions since slides may keep their original sedimentary signature a combined analysis and numerical modeling of geochemical physical properties and hydro acoustic data could be applied in order to reconstruct the sedimentary history we present first order estimates of the dating of sedimentary events for an area where conventional stratigraphic methods failed to this day the results of the investigated sites suggest that present day conditions are the result of events that occurred decades to thousands of years ago and promote a persisting mass transport from the shelf into the deep sea depositing high amounts of reactive compounds the high abundance of reactive iron phases in this region maintains low hydrogen sulfide levels in the sediments by a nearly quantitative precipitation of all reduced sulfate by aom for the total region we estimate a so 4 or ch 4 flux of 6 6 10 10 moles per year into the zone of aom projected to the global continental slope and rise area this may sum up to about 2 6 10 12 moles per year provided that the sulfur is completely fixed in the sediments it is about twice the global value of the recent global sulfur burial in marine sediments of 1 2 10 12 moles per year as previously estimated thus aom obviously contributes very significantly to the regulation of global sulfur reservoirs which is hitherto not sufficiently recognized this finding may have implications for global geochemical models as sulfur burial is an important control factor in the development of atmospheric oxygen levels over time

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

sediment chemistry and magnetic properties in an anomalously reducing core from the eastern mediterranean sea abstract in core kc19c 19 6 m long recovered in the abyssal plain between crete and cyprus in the eastern mediterranean a large number of organic rich layers sapropels occur which correlate to maxima in the insolation curve in contrast to other sites in the eastern mediterranean porewaters contain sulfide below a few meters below seafloor mbsf geochemical analyses were performed on the porewaters ammonium alkalinity sulfate manganese iron bisulfide chloride eh ph and sediments organic carbon barium total sulfur total iron manganese pyrite dithionite extractable iron in addition a series of magnetic parameters and ratios nrm arm irm in arm irm s ratio arm 20mt arm in were determined in the top of the sediments fe and mn hydr oxides occur at the oxic suboxic boundary just above the youngest sapropel si2 these hydr oxides appear to be more easily demagnetized by means of alternating fields than deeper hydr oxides which presumably are of detrital origin the transition from suboxic to anoxic sediments is located at 2 mbsf sulfide is produced possibly during sulfate reduction through anoxic methane oxidation at 17 5 mbsf from 17 5 mbsf sulfide migrates upward titrating reactive fe resulting in pyrite formation in the entire sediment column up to 2 mbsf at this depth the upward sulfide flux has been totally consumed by reaction with solid phase fe and dissolved fe ii diffusing downward from the suboxic zone above from 2 mbsf downward magnetic intensities are significantly reduced indicating reductive dissolution of fe oxide minerals and pyrite formation as a consequence no reliable nrm data can be obtained in the lower half of the core

tracing water column euxinia in eastern mediterranean sapropels s5 and s7 abstract sapropels s5 and s7 formed in the semi enclosed eastern mediterranean sea ems during peak interglacial periods mis5e and mis7a respectively are considered among the most strongly developed quaternary sapropels this study investigates the redox dynamics of the water column during their formation via fe isotope and fe speciation studies of cores taken at 2550 m depth at site odp 967 both sapropels show an inverse correlation between 56fe and fet al with slopes mostly matching that found for the black sea pointing to a benthic shelf to basin shuttle of fe and subsequent precipitation of fe sulphides in euxinic bottom waters an exception to these black sea type trends occurs during the later peak stages of s7 where the negative 56fe fet al slope shallows fe speciation studies reveal that the dominant highly reactive fe phase fehr in the sapropels is pyrite with fe oxyhydr oxides forming the second major mineral component correspondingly fehr fet plots show increased strengthening of anoxic water conditions during the passage from pre sapropel sediment into the sapropel nevertheless despite the evidence for euxinic conditions from both fe isotopes and high mo concentrations in the sapropel fepy fehr ratios remain below values commonly used to identify water column euxinia this apparent contradiction is ascribed to the sedimentary preservation of a high flux of crystalline fe oxyhydr oxide minerals to the basin which resulted in a relatively low degree of sulphidation despite the presence of euxinic bottom waters thus the operationally defined ferruginous euxinic boundary for ems sapropels is better placed at fepy fehr 0 6 which is somewhat below the usually ascribed lower limit of 0 7 consistent with the significant presence of crystalline fe oxyhydr oxides the change in the 56fe fet al slope during peak s7 is ascribed to an enhanced monsoon driven flux of detrital fe iii oxides from the river nile into the ems basin and comcomitant diagenetic sulphidation euxinic water column conditions in sapropel s5 and s7 are interpreted here to reflect the positive balance between dissolved sulphide formation and rates of reductive dissolution of fe oxyhydr oxide minerals both of these parameters in turn depend on the extent to which water overturn times are reduced and export productivity increased during sapropel formation

sedimentary organic carbon to phosphorus ratios as a redox proxy in quaternary records from the mediterranean abstract in this study organic carbon to organic phosphorus c org p org and total phosphorus c org p tot ratios as bottom water redox proxies are explored for two eastern mediterranean sediment records extending back 600 700 kyrs cores kc19c 19 6 m long 2750 m water depth and kc01b 37 0 m long 3643 m water depth contain numerous organic rich layers sapropels throughout the two cores variations found in the c org p ratios correspond to those for other redox proxies such as total s contents and v al ratios accordingly these are interpreted as variations in bottom water oxygenation and inter sapropel redox variability in core kc19c the original c org p signals seem to have been preserved despite intense post depositional sulfidization high resolution p fractionation data of sapropel s5 from a third core ps25pc 3304 m water depth showing high and relatively stable c org p org ratios indicate that sapropel s5 at this deep location was deposited under permanently reducing conditions while p regeneration from organic matter was intense net p burial increased in the sapropel due to enhanced burial of inorganic calcium phosphate likely biogenic ca p sediment p contents and c org p tot ratios in s5 are variable reflecting short term changes in marine conditions productivity redox and sediment chemistry the c org p org and c org p tot ratios thus provide valuable insight into paleoceanographic conditions and pathways of p cycling for mediterranean sediment records extending back at least 600 700 kyrs

paleoenvironmental changes in the east japan sea during the last 48 ka indications from high resolution x ray fluorescence core scanning paleoceanographic changes in the east japan sea during the late quaternary based on high resolution elemental variations particularly correlations between dark light laminations and millennial scale climatic changes have remained poorly understood because of the lack of the high resolution proxies the recent application of micro x ray fluorescence xrf core scanning provides the potential for high resolution study on the laminations deposited in the east japan sea in this study we present a geochemical study by using micro xrf core scanning on a 730 cm core recovered from the east japan sea elemental variations and factor analysis indicate that the sedimentary environment changed from anoxic to suboxic conditions from marine isotope stage mis 2 3 to mis 1 which is induced by increased contribution of high salinity sea water from the open ocean due to the rising sea level the dark and light laminations during mis 2 3 were correlated with dansgaard oeschger cycles and summer monsoon proxy with dark colored sediments related to higher terrigenous concentration corresponding to warm moist and enhanced summer monsoon period during the interstadial period more terrigenous sediments were transported to the east japan sea via the strengthened fluvial discharge from the surrounding continents caused by enhanced monsoon rainfall thus the development of the east asian summer monsoon and consequent variations in fluvial discharge would have significantly affected the paleoceanographic conditions in the east japan sea during the mis 2 3 sea level lowstand copyright 2012 john wiley sons ltd

trace metals in holocene coastal peats and their relation to pyrite formation nw germany abstract three drill cores from the marshlands of nw germany which cover the entire holocene were analyzed at high resolution for bulk composition al fe selected trace metals and stable sulfur isotopes the drill cores contain two lithological types of peat i basal peats overlying pleistocene sands and ii intercalated peats situated between clastic sediments of predominantly marine origin the peat layers are characterized by distinct enrichments in pyrite due to microbial sulfate reduction under almost open system conditions with respect to seawater sulfate as shown by sulfur isotope partitioning the main fe source seems to be the freshwater environment the determination of dissolved and particulate fe of channels and small rivers close to the study area revealed a 50 fold higher fe content of the freshwater environment when compared with north sea water pyrite enrichments are explained by two scenarios i pyrite formation coincides with fen reed peat growth basal and intercalated under the influence of a brackish water zone salinity app 5 15 and ii pyrite was formed after peat growth in the lowest limnic basal peat intervals maximum pyrite accumulation ts 28 occurs in latter peats that contain thin clastic layers as a result of tidal channel activities after peat formation the occurrence of clastic layers may have favoured the inflow of saline groundwater the peat layers are also characterized by enrichments in redox sensitive trace metals as mo re u and cd whereas co cr cu mn ni pb tl and zn reflect the geogenic background leaching experiments have shown that as co cu mo re and tl are predominantly fixed as sulfides and or incorporated into pyrite the remaining trace metals show no distinct trends only cr reveals a strong relation to the lithogenic detritus seawater is the dominating source for as cd mo re and u the remaining trace elements seem to have a freshwater source similar to fe in contrast to the distribution of pyrite highest amounts of redox sensitive trace metals are seen in fen reed peats basal and intercalated that were formed under a direct influence of seawater and brackish water respectively therefore we suggest that saline groundwater entering the basal peats was probably depleted in redox sensitive trace metals e g owing to microbially induced reduction of trace metals and subsequent precipitation as sulfides or fixation by organic matter

on the late pleistocene holocene sapropel record of climatic and oceanographic variability in the eastern mediterranean sapropels and intercalated marls in a piston core from the eastern mediterranean are chemically and mineralogical distinct kaolinite smectite and total s contents fe a1 ba a1 co a1 mo a1 and v a1 are higher whereas quartz mg calcite illite contents si a1 ti a1 k a1 rb a1 and zr a1 are lower in the sapropels missing and ghost sapropels are identified by mineralogical and chemical properties that are not prone to diagenesis primary production was higher ba a1 and bottom water and or interstitial oxygenation was lower co a1 mo a1 ni a1 and v a1 during sapropel formation wind speeds quartz clay si a1 and zr a1 and bottom water salinities mg calcite calcite were higher during periods of marl formation sapropels represent a fundamentally different sedimentary facies whose formation is linked to changes in the hydrological balance in the basin driven by precessionally modulated changes in monsoon strength and subtropical precipitation changes which altered circulation production and sediment source areas

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

molybdenum isotope multiple sulfur isotope and redox sensitive element behavior in early pleistocene mediterranean sapropels abstract organic rich sediments sapropels deposited in the mediterranean are presumed to have formed during periods of increased productivity and or deep water oxygen depletion possibly including the development of sulfidic conditions euxinia geochemical redox proxies re mo mo isotopes v fe al and multiple s isotopes in 8 sapropels from the pleistocene confirm water column euxinic conditions of varying intensity during sapropel deposition these same proxies indicate an oxic origin for hemipelagic sediments deposited between sapropel forming episodes in one intensively sampled sapropel deposited between 1 450 and 1 458 ma changing concentrations of organic carbon ba re mo v and fe al track one another closely reflecting coupling between water column euxinia and biological productivity multiple s isotope data from this sapropel suggest that the redox interface where oxidative sulfur cycling occurred was present in the sediments during hemipelagic sedimentation but moved into the water column during sapropel deposition molybdenum isotopes of these 8 sapropels encompass a range of values 98mo 0 2 to 1 7 but are all 98mo depleted relative to seawater 98mo 2 3 suggesting that quantitative removal of mo did not occur this finding contrasts with modern black sea sediments in general re mo ratios in sapropels are greater than in modern seawater implying that the water column was not sufficiently sulfidic during sapropel forming episodes to induce complete removal of both these elements surprisingly the heaviest 98mo values are found within hemipelagic sediments very few of the hemipelagic samples preserve the negative 98mo values commonly associated with modern oxic marine sediments many of the hemipelagic samples also contained higher concentrations of re and mo than are common in oxic sediments these features may be attributable to diffusion from the sapropels of a 98mo enriched component into the hemipelagic sediments

sulphur speciation in anoxic hypersaline sediments from the eastern mediterranean sea abstract the anoxic hypersaline tyro and bannock basins are among the most sulphidic bodies of water in the marine environment h2s 2 mm we report the distribution of elemental sulphur acid volatile sulphur avs organic polysulphides humic sulphur 0 5 m naoh extractable and pyritic sulphur in the sediments from these basins pyritic sulphur appears to be the main phase of inorganic reduced sulphur 50 80 of the total sulphur pool and is at the same level about 250 moles per gram dry weight in cores recovered from the two basins remarkably humic sulphur has been found to account for 17 28 of the total sulphur pool in the tyro basin and for 10 43 in the bannock basin sulphur isotope data show negative 34s values for both pyritic sulphur 34s 19 c to 39 and humic sulphur 34s 15 to 30 this indicates that both pyritic and humic sulphur originate from microbially produced hzs neither basin shows a significant correlation between pyritic sulphur and organic carbon suggesting syngenetic pyrite formation additionally the degree of pyritization in these sediments dop is 0 62 indicates that pyrite formation is limited by the reactivity of fe humic sulphur correlates with the pyritic sulphur distribution and seems to be related with gelatinous pellicles bacterial mats at the interface between oxic seawater and brine both pyritic and humic sulphur can be formed in the water column at the interface of oxic seawater and brine by a syngenetic pathway about 5 of the pyrite is formed in the sediments by diagenetic processes the presence of a bacterial mat and high hzs content in the brines favour such conditions however most of the humic sulphur inventory can be supported by diagenetic processes although these basins differ in their major element chemistry their reduced sulphur species chemistry appears to be similar

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

high resolution geochemical and micropalaeontological profiling of the most recent eastern mediterranean sapropel abstract a combined geochemical and micropalaeontological study of the most recently deposited sapropel s1 from the eastern mediterranean sea is reported from two cores in which the s1 sapropel units were rapidly deposited 15 and 20 cm ky 1 such rapid accumulation rates have largely protected the two s1 units from post depositional oxidation effects and allow a high resolution investigation of conditions before during and after s1 formation the cores are from the adriatic and aegean seas and both record a simultaneous diminution in intensity of sapropel development at 7500 conventional radiocarbon years that divides both visual s1 units into two approximately equal lobes detailed foraminiferal analysis of the aegean core reveals fluctuations in benthic foraminifera species that indicate anoxic or near anoxic bottom water conditions during formation of the upper and lower lobes the central s1 section shows a temporary repopulation by an opportunistic benthic species g orbicularis indicative of improved bottom water oxygen levels the appearance and disappearance of this species in the central section and its reappearance just before the end of s1 times also coincides with increases in abundance of pelagic foraminifera characteristic of cooler surface water conditions and with local mn peaks in the sapropel these features are interpreted as indications of increased deep water ventilation and bottom water o 2 levels centred during s1 time although the s1 c org contents are low at 1 2 wt because of dilution by high detrital fluxes a set of elements ba cr cu mo ni s se u v and zn generally present in other s1 units older sapropels and black shales is clearly present at enhanced levels sulfur enrichment is well correlated with the c org content throughout s1 and fes 2 formation accounts for the bulk of the observed s enrichment

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

a model for iron deposition to euxinic black sea sediments sulfur isotope and c s fe elemental data from the lower devonian siegenian emsian hunsruck slate of germany allow the conditions that led to the pyritization of soft bodied fossils to be determined the slates preserving pyritized soft tissues generally contain low concentrations of organic matter 0 3 0 4 percent c and pyrite sulfur 0 0 2 percent s respectively but are unusually rich in total and hcl extractable iron concentrations of iron are significantly lower in samples of the hunsruck slate from areas where fossils lack pyritized soft tissues the fossil pyrite is very enriched in s 34 compared to fine grained disseminated pyrite in the adjacent slates delta fossil sediment 10 to 50 permil suggesting that pyritization of the fossils persisted into later stages of authigenic mineralization pyrite formation in the sediments was limited by the low concentrations of metabolisable organic matter leaving residual sulfate and iron available for continued fossil pyritization in organic rich microenvironments a diffusion with precipitation model indicates that a critical control on the initial preservation of readily metabolisable soft tissue in this way is the presence of high concentrations of sediment iron capable of being solubilized during shallow burial diagenesis in association with low concentrations of metabolisable organic matter in the matrix pore waters rich in dissolved iron allow the sulfide generated by the decay of readily metabolisable soft tissue to be trapped efficiently within the carcass

sources of iron for pyrite formation in marine sediments more than two hundred aerobic continental margin aerobic deep sea dysaerobic and anaerobic euxinic sediments have been examined for their variations in different operationally defined iron fractions each of which represents a different reactivity towards dissolved sulfide aerobic continental margin deep sea and dysaerobic sediments contain similar contents of highly reactive iron dithionite soluble iron plus pyrite iron poorly reactive iron iron soluble in hcl less that soluble in dithionite and unreactive iron total iron less that soluble in hcl by contrast non turbidite euxinic samples from the black sea as well as euxinic samples from the cariaco basin and framvaren are enriched in highly reactive iron these sediments contain a small lithogenous fraction and a large biogenous organic c rich fraction which decays by sulphate reduction in an iron rich water column to form pyrite rich sediment other anaerobic euxinic samples from the black sea orca basin and kau bay contain lower concentrations of biogenous sediment and are not therefore enriched in highly reactive iron degrees of pyritization dop for all the aerobic dysaerobic and anaerobic euxinix samples except those low in biogenous material are consistent with analogous ancient sediments and indicate that most pyrite formation occurs form the highly reactive iron fraction

sulfur biogeochemistry and isotopic fractionation in shallow groundwater and sediments of owens dry lake california groundwater and sediment samples 1 m depth at sites representative of different groundwater pathways were collected to determine the aqueous speciation of sulfur and the fractionation of sulfur isotopes in aqueous and solid phases in addition selected sediment samples at 5 depths from oxic to anoxic layers were collected to investigate the processes controlling sulfur biogeochemistry in sedimentary layers pyrite was the dominant sulfur bearing phase in the capillary fringe and groundwater zones where anoxic conditions are found low concentrations of pyrite b5 9 g kg 1 coupled with high concentrations of dissolved sulfide 4 81 to 134 7 mg l 1 and low concentrations of dissolved fe generally b 1m g l 1 and reducible solid phase fe indicate that availability of reactive fe limits pyrite formation the relative uniformity of down core isotopic trends for sulfurbearing mineral phases in the sedimentary layers suggests that sulfate reduction does not result in significant sulfate depletion in the sediment sulfate availability in the deeper sediments may be enhanced by convective vertical mixing between upper and lower sedimentary layers due to evaporative concentration the large isotope fractionation between dissolved sulfate and sedimentary sulfides at owens lake provides evidence for initial fractionation from bacterial sulfate reduction and additional fractionation generated by sulfide oxidation followed by disproportionation of intermediate oxidation state sulfur compounds the high salinity in the owens lake brines may be a factor controlling sulfate reduction and disproportionation in hypersaline conditions and results in relatively constant values for isotope fractionation between dissolved sulfate and total reduced sulfur d 2005 elsevier b v all rights reserved

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

the architecture of organic matter and its pores in highly mature gas shales of the lower silurian longmaxi formation in the upper yangtze platform south china the nanometer scale architecture of organic matter om and associated pores in highly mature gas shales from the lower silurian longmaxi formation in the upper yangtze platform of south china were investigated using field emission scanning electron microscopy sem focused ion beam sem and low pressure gas n2 and co2 adsorption bulk pore characterization the longmaxi shale comprises fine grained siliciclastic rocks deposited in a marine shelf environment which was dominated by quartz and clay minerals four porous om types were found in the longmaxi shale on the basis of the chemical composition and spatial occurrence of om including 1 isolated original om particles 2 om clay mineral complexes 3 om heavy mineral complexes and 4 secondary migrated bituminous om the pores in the particulate om are not homogeneously distributed and the processes leading to different pores depend on the specific om type the nature of om hosted pores is a result of several factors such as primary porous kerogen mechanical compaction organic inorganic interactions gaseous and liquid hydrocarbon generation retention and expulsion pore volumes and specific surface areas of the longmaxi shale derived from low pressure n2 and co2 adsorption experiments reveal positive linear relationships with total organic carbon contents which indicates that the pore systems in the highly mature longmaxi shale are dominated by om hosted pores additionally the om hosted pores appear connected compared to pores in the mineral matrix therefore the om hosted pore systems offer the preferential storage space and primary migration pathways for natural gas in the longmaxi shale reservoir

polar mesosphere summer echoes pmse at halley 76 s 27 w antarctica 1 polar mesosphere summer echoes pmse are a pointer to summer mesospheric conditions and have fuelled the debate over temperature differences between the antarctic and arctic mesopause regions however few pmse observations have ever been made in antarctica we present initial pmse observations from halley 76 s 27 w taken during january and february 2004 these are the first observations at such high southern latitude the first using a dynasonde for detection and the first at 28 mhz pmse are frequently observed and exhibit a double maximum in diurnal occurrence in contrast to published observations at similar arctic latitudes the pmse season ends slightly earlier relative to summer solstice than in the arctic the strength of the pmse appear similar to pmse observed in the northern hemisphere this is consistent with published falling sphere measurements showing similar summer mesopause temperatures in january in the antarctic as in july in the arctic

climate control of sulfate influx to lake hovsgol northwest mongolia during the last glacial postglacial transition constraints from sulfur geochemistry abstract changes in sulfur cycles in lake hovsgol northwest mongolia are discussed on the basis of total organic carbon toc total sulfur ts concentrations and stable sulfur isotope ratios 34 s in two sediment cores x104 and x106 covering the last glacial to the present correlation plots of toc and ts c s plots of the sediment cores indicate dissolved sulfate enrichment in sediment pore water and high sulfate reducing bacteria srb activity during the climate transition from the last glacial to postglacial period lg pg transition from ca 21 to 11 6 cal ka bp in addition positive shifts of 34 s values from 3 7 to 32 6 were observed during the lg pg transition these results suggest a large influx of 34 s rich dissolved sulfate into the lake during this period the 34 s rich dissolved sulfate may have accumulated on the shore wetlands and marshes of lake hovsgol during the last glacial period owing to the increase in atmospheric precipitation and lake level rise during the lg pg transition the 34 s rich dissolved sulfate may have been supplied from the shore to the lake increased sulfate influx during the lg pg transition has also been observed in a lake baikal sediment core our new sulfur geochemical data shows past environmental changes particularly moisture changes within continental asia during the climate transition

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

glacier shrinkage in the daxue and danghenan ranges of the western qilian mountains china from 1957 to 2010 changes in glaciers in the daxue and danghenan ranges were analyzed based on topographic maps satellite images and a digital elevation model dem the results indicate that from 1957 1966 to 2010 the total area and ice volume for the investigated glaciers declined by 17 21 and 24 10 in these respective ranges from 1957 to 2010 the total area and ice volume in the glaciers in the daxue range declined by 16 03 0 30 a 1 and 22 40 respectively with a mean reduction of 0 133 km2 for an individual glacier these glaciers retreated by an average of 258 m 3 4 m a 1 from 1966 to 2010 the total area and ice volume for the glaciers in the danghenan range declined by 18 32 0 42 a 1 and 25 70 with a mean reduction of 0 111 km2 for an individual glacier these glaciers retreated by an average of 159 m 3 6 m a 1 the rate of glacier retreat on the south facing slopes was faster than that on the north facing slopes the area of glaciers on the south and north slopes of the daxue range declined by 22 82 and 15 51 respectively and the area of glaciers on the south and north slopes of the danghenan range declined by 22 39 and 16 76 respectively an analysis of the general trend of climatic change in the study area revealed that rapidly rising air temperatures were most likely the major factor causing the loss of glacier ice within the study area compared with other glaciers in the eastern and middle qilian mountains glaciers in the western qilian mountains appeared to be losing mass at a slower rate the differences of glacier changes in the eastern middle and western qilian mountains are mainly caused by the combination of climatic conditions and glacier morphologic factors

paleoproductivity and paleoredox conditions during late pleistocene accumulation of laminated diatom mats in the tropical west pacific paleoproductivity and paleoredox conditions were reconstructed in a sediment core in the parece vela basin of the eastern philippine sea the core consists of three units from youngest to oldest 1 laminated diatom mats ldm formed by ethmodiscus rex during the last glacial maximum similar to 18 28 kyr b p 2 diatomaceous clay dc and 3 pelagic clay pc elevated levels of export productivity during ldm deposition are indicated by high values for excess ba opal content and toc ti ratios estimated rates of organic carbon degradation ca 98 opal mass accumulation average 1322 g m 2 yr 1 and corrected organic carbon flux average 248 g m 2 yr 1 are comparable to high productivity regions of the modem ocean the ldm is also characterized by moderate enrichment of redox sensitive elements such as u mo cd and zn highly s 34 depleted pyrite sulfur isotopic compositions indicating bacterial sulfate reduction in a sulfate unlimited system and c s fe systematics reflecting limitation of pyrite formation by organic matter rather than reactive fe availability these features suggest mainly suboxic conditions in bottom waters but development of sulfidic anoxic conditions at or close to the sediment water interface association of intensified anoxia with productivity maxima indicates that export production was a more important control on bottom water redox conditions than lateral ventilation the dc and pc accumulated under oxic to suboxic conditions our observations suggest that redox environments during deposition of laminated marine sediments are more complicated and varied than previously thought and thus the use of sediment lamination as an indicator of anoxic bottom water conditions must be approached cautiously c 2012 elsevier b v all rights reserved

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

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

paleoceanographic implications of nitrogen and organic carbon isotopic excursions in mid pleistocene sapropels from the tyrrhenian and levantine basins mediterranean sea abstract comparison of the total nitrogen and organic carbon isotopic compositions of sediment sequences from the tyrrhenian and levantine basins that contain three same age sapropels reveals evidence of both similarities and differences in mid pleistocene sapropel forming conditions in the western and eastern mediterranean sea total 15 n values systematically decrease at both locations from 5 in background sediments to 1 in the sapropels the lower 15 n values signify that nitrogen fixation was important to the increased marine productivity implied by the higher organic carbon concentrations which is consistent with widespread salinity stratification of surface waters when sapropels accumulated organic 13 c values systematically increase from 25 in the background sediments to 22 in the sapropels at the tyrrhenian site which confirms that increased marine productivity accompanied sapropel deposition in contrast 13 c values decrease in the sapropel layers in the levantine basin even though organic carbon concentrations are higher in these sapropels the different types of 13 c excursions associated with increased organic matter production at the two locations indicates a difference in the dissolved carbon pool from a combination of greater fluvial delivery of continental carbon and stronger recycling of organic matter in the levantine sea than in the tyrrhenian sea this difference implies that the shifts to wetter climate during times of sapropel deposition were stronger in the eastern than in the western mediterranean

enhanced deepwater circulation and shift of sedimentary organic matter oxidation pathway in the okinawa trough since the holocene 1 high resolution biogeochemical and magnetic property analyses of a 20 kyr sediment core in the okinawa trough revealed a significant upward decrease in total sulfur content ts at around 10 cal ka bp which coincides with a transformation from foliation to anomalous sedimentary magnetic fabric which indicates an enhancement of deepwater circulation synchronous change in biogeochemical and magnetic properties in sediments was likely triggered by the intensified kuroshio current which strengthened surface water productivity and the relative input of marine organics to the sediments however this event did not promote sedimentary sulfur burial instead the synchronously enhanced deepwater circulation switched the organic carbon oxidation pathway from sulfate reduction to aerobic respiration which resulted in ts depleted sediments

the diagenetic formation of metal rich layers in sapropel containing sediments in the eastern mediterranean two cores recovered from different locations in the eastern mediterranean contain intercalations of organic rich sapropels in organic poor hemipelagic sediments in both cores enrichments of mn and fe were found in the oxidised section of the sediment above the sapropel s1 the sediments followed a diagenetic cycle which began after the sapropel formation finished about 7000 years ago first during a non steady state diagenetic phase metal rich layers were formed at a downward moving oxidation front the front decelerated at the top of the sapropel as a consequence of increasing amounts of corg and sulphides that had to be oxidised during the second part of this non steady state phase the oxidation front starts moving upwards with respect to the sapropel manganese is remobilised in preference to iron due to thermodynamics reinforced by kinetics when the upward movement of the oxidation front becomes equal to the sedimentation rate steady state is established with respect to the new organic poor sedimentary circumstances at location 31g1 the system is at or close to steady state at location 9g1 however this steady state phase has never been reached between 1900 and 1350 years bp the organic carbon accumulation rate probably increased suddenly inducing a retreat of the oxidation front and the non steady state formation of double peaks

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

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

magnetic properties and geochemistry of the active oxidation front and the youngest sapropel in the eastern mediterranean sea summary magnetic properties irm arm xin s ratio at 0 3 t room temperature rt hysteresis and thermomagnetic curves and geochemical data fe s mn al ti organic c were studied in two eastern mediterranean boxcores abc26 and bc19 at a resolution of 3 5 mm the boxcores contain sapropel s1 9 6 kyr bp at a few decimetres below seafloor the magnetic fraction consists predominantly of single domain sd to pseudo singledomain psd magnetite in the entire cores the original input of magnetic grains comes from two sources aeolian dust both cores and volcanic ash from the minoan eruption of santorini core bc19 only non steady state diagenesis has changed the magnetic mineralogy considerably in these alternating organic rich organic poor sediments during deposition of sapropel s1 reductive diagenesis and pyritization in and just below the sapropel caused lower magnetic intensities coarser magnetic grain sizes and partial maghemitization in thermomagnetic curves two types of pyrite can be identified one oxidizes below 450 uc and the other above 450 uc the higher oxidation temperature is predominantly found below the sapropel this may be related to the microtexture of pyrite which is euhedral below sapropels and mainly framboidal within sapropels since the end of sapropel deposition a downward moving oxidation front has oxidized the upper half c 5 cm of the sapropel the oxidized part of the sapropel is enriched in diagenetically formed fe oxides with relatively high coercivity and arm the maximum coercivity is found in a distinct layer between the present day mn and fe redox boundaries at the top of the unoxidized sapropel the freshly precipitated fe oxides in this centimetre thick layer contain a mixture of superparamagnetic sp grains and high coercivity sd magnetite higher in the oxidized zone the freshly precipitated fe oxides have aged into generally slightly lower coercivity sd grains with relatively high arm in addition to the diagenetic formation of fe oxides at the top of the sapropel formation of a ferrimagnetic fe monosulphide may have occurred within the sapropel during later stages of diagenesis which may have enhanced the arm signal in the organic rich interval in particular

pyrite oxidation during sample storage determines phosphorus fractionation in carbonate poor anoxic sediments abstract we investigated the phosphorus p and iron fe fractionation in four cores with anoxic sediments deposited during the mid cretaceous oceanic anoxic event 2 94 ma and the paleocene eocene thermal maximum 55 ma that were exposed to oxygen after core recovery surprisingly p associated with iron oxyhydroxides fe bound p was a major p phase in these laminated sediments deposited under euxinic conditions a significant fraction of total fe was present as poorly crystalline ferric fe this fraction increased with increasing storage time of the investigated cores in carbonate poor samples fe bound p accounted for up to 99 of total p and its abundance correlated with pyrite contents in samples with higher caco3 contents 5 wt in the investigated samples p was mostly present in authigenic ca p minerals irrespective of pyrite contents we conclude that the p fractionation in anoxic carbonate poor sediments is strongly affected by pyrite oxidation that occurs when these sediments are exposed to oxygen pyrite oxidation produces sulfuric acid and iron oxyhydroxides the abundance of poorly crystalline fe oxyhydroxides provides further evidence that these were indeed formed through recent post recovery oxidation rather than in situ tens of millions of years ago the acid dissolves apatite and the released phosphate is subsequently bound in the freshly formed iron oxyhydroxides pyrite oxidation thus leads to a conversion of authigenic ca p to fe bound p in more calcareous samples caco3 can act as an effective buffer against acidic dissolution of ca p minerals the results indicate that shielding of sediments from atmospheric oxygen is vital to preserve the in situ p fractionation and to enable a valid reconstruction of marine phosphorus cycling based on sediment records

magnetic mineral inventory of equatorial atlantic ocean marine sediments off senegal glacial and interglacial contrast summary in complex sedimentary environments with different sources of the magnetic particles it is vital that all factors contributing to and affecting the magnetic signals be well understood for a better constrained interpretation of palaeomagnetic and climatic data palaeoclimatically driven signals may be convolved with volcanic and cosmogenic sources and diagenesis may alter the primary magnetic mineral assemblage rock magnetic methods and electron microscopy provide suitable means to characterize magnetic assemblages in this study of core retrieved sediments from the last 150 kyr off the coast of senegal nw africa the occurrence of magnetic spherules of volcanic origin and cosmogenic particles appeared to be insignificant in glacial stages ferrimagnetic iron and iron titanium oxides magnetically dominate with few signs of a diagenetic overprint low and room temperature magnetic results reveal evidence for haematite and goethite while haemoilmenite and titanomagnetite were identified from low temperature ac susceptibility measurements and sem observations in contrast the interglacial samples appeared to have been severely affected by diagenesis with pyrite making up over 50 per cent of the iron bearing phases the verwey transition observed at 110 k confirms the presence of magnetite the glacial and interglacial contrast reveals the close link between northwest african climate and the magnetic mineralogy of the sediments

sedimentary pyrite formation in the arabian sea abstract in this study pyrite formation in relation to environmental conditions was investigated in sediment records from the northern arabian sea considering the low bottom water oxygen concentrations in the oxygen minimum zone omz and the high rates of primary productivity on the oman and pakistan margins sedimentary pyritic s concentrations are unexpectedly low on average 0 4 wt compared to organic contents sediments located deeper than the omz exhibit a good correlation between organic carbon and reduced sulphur conversely the c versus s distribution for omz sediments indicates a partial decoupling between organic carbon accumulation and pyrite formation early post depositional sulphidisation resulted in the diagenetic sulphur enrichment of organic poor intervals this is evidenced by the presence of pyrite enrichments located below organic rich intervals pyrite formation in the sediments within the arabian sea omz was limited by the availability of reactive iron oxides this was caused by the low oxygen concentrations of the omz which resulted in the reduction of iron oxides in the water column or at the sediment water interface however on the basis of the relatively high sedimentary c s ratios and the presence of bioturbation it is clear that no euxinic conditions developed in the omz in the arabian sea during the last 120 kyr

review and new aspects concerning the formation of eastern mediterranean sapropels abstract in this paper it is proposed that the formation of eastern mediterranean sapropels occurred in an anti estuarine type of circulation which was to some degree weakened relative to the present in response to reduction of the eastern mediterranean excess of evaporation over freshwater input this reduction of excess evaporation would have been imposed by intensifications of 1 the indian ocean summer sw monsoon influencing the eastern mediterranean via increased nile discharge and 2 the system of mediterranean depressions an element of the westerly atlantic system causing increased precipitation and decreased evaporation both the indian ocean summer monsoon and the westerly atlantic system would be intensified in response to the occurrence of distinct minima in the cycle of precession it is demonstrated that reduced excess evaporation whether or not coinciding with global phases of deglaciation would lead to reduction of surface water salinities in the eastern mediterranean causing isolation of previously formed high salinity cooler deep water thus mixing was severely reduced possibly even restricted to eddy diffusion with only occasional convective events that because of the existing density gradient hardly ever would reach the deepest parts of the basin the consequently diminished oxygen advection down from a few hundred meters in the water column favoured preservation of the sinking organic matter this would however suffice only to enable the formation of sapropels with low organic carbon contents the high organic carbon contents observed in various sapropels are argued to reflect superimposed increases of export production the described scenario accounts for previously reported 1 increases of organic carbon content with increasing depth of deposition within individual sapropels and 2 asymmetrical sequences of sapropel deposition characterized by gradual build up and rather abrupt ending it is furthermore in agreement with 3 isotopic and faunal reconstructions of the history of exchange transports through both the strait of sicily and the strait of gibraltar and 4 faunal and floral reflections of the presence or absence of a distinct deep chlorophyll maximum with its associated increases in export production indicating the presence or absence of a shallow pycnocline within the euphotic layer moreover the described scenario 5 is in no way conflicting with the reports of sapropels in the western mediterranean and 6 seems to be endorsed by occasionally intercalated intervals suggestive of somewhat improved oxygenation amidst anoxic benthic desert levels a situation that has been observed in a few quaternary and pliocene sapropels

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