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Gert J. De Lange - One of the best experts on this subject based on the ideXlab platform.
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riverine supply to the eastern mediterranean during last interglacial Sapropel s5 formation a basin wide perspective
Chemical Geology, 2018Co-Authors: Amalia Filippidi, Gert J. De Lange, G R DaviesAbstract:Abstract Organic-rich Sapropel sediments were repeatedly deposited in the eastern Mediterranean Sea (EMS), in response to insolation-driven freshwater forcing. However, the exact freshwater sources and causal associated paleoclimate-related processes remain unresolved. Sapropel S5, formed during the insolation maximum of the last interglacial, is one of the most intensely developed Sapropels of the Late-Quaternary. Here, detrital sediments of Sapropel S5 obtained from 8 cores, together with 13 EMS surface samples, are analyzed for major elements, rare earth elements (REE), and Sr and Nd isotopes. This permits a basin-wide investigation of the source and distribution of river-borne material to the EMS for Sapropel S5, and its comparison to the present-day and the Holocene Sapropel S1 period. During the Sapropel S5, there was minor Saharan dust input. The marked east–west geochemical gradient in S5 detrital sediments across the EMS is therefore attributed to mixing between fluvial contributions, being Nile discharge, Aegean/Adriatic riverine inputs, and Libyan-Tunisian paleodrainage fluxes. The offshore distribution of Nile sediments during Sapropel S5 was comparable to those during S1 and the present. The Nile sediment contribution appears to be only dominant for the Levantine Basin, decreasing to negligible values south of Crete. This rather limited sediment delivery, despite inferred increased runoff during S5, is related to denser vegetation cover on the Ethiopian Highlands. By contrast, small rivers around the Aegean (and Adriatic) Sea brought large amounts of detrital material into the EMS. This is particularly noticeable around Crete and the northern Ionian Sea. The enhanced riverine input is probably due to strong precipitation seasonality over the northern EMS borderlands, particularly for the early phase of the last interglacial maximum. Furthermore, there are substantial fluvial contributions from the Libyan-Tunisian margin to the Ionian Sea sediments, in particular during the last part of Sapropel S5. The inferred river-borne material was transported via paleodrainage systems reactivated by intensified monsoon precipitation, and derived from central-Saharan mountains. Compared to Sapropel S1, these S5-related paleodrainage fluxes were not only stronger, but also had a more predominant provenance from eastern rather than western Libya. In addition, a similar, averaged endmember of Saharan dust sources is revealed by REE signatures.
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marine productivity leads organic matter preservation in Sapropel s1 palynological evidence from a core east of the nile river outflow
Quaternary Science Reviews, 2015Co-Authors: Rick Hennekam, Gert J. De Lange, Henk Brinkhuis, Niels A G M Van Helmond, Timme H Donders, F P M Bunnik, Francesca SangiorgiAbstract:The formation of Eastern Mediterranean organic matter rich deposits known as Sapropels is the results of two mechanisms: (enhanced) marine productivity and preservation of organic material at depth. However, their relative contribution and their leads and lags with respect to each other remain elusive. Here, we address these questions by studying sediments deposited prior to, during, and after the most recent Sapropel (S1, ~10e6 calibrated ka before present, BP) with an integrated marine and terrestrial palynological approach, combined with existing and newly generated geochemical data. The studied core was retrieved from an area under strong influence of the Nile outflow and has high average sediment accumulation rates allowing a high temporal resolution (of several decades to centuries). Marine productivity, as reconstructed with total dinocyst accumulation rates (ARs) and biogenic CaCO3 content, starts to increase ~1 ka prior to Sapropel formation. A shift in the dinocyst taxa contributing tothe productivity signal at Sapropel onset indicates the rapid development of (seasonal) water column stratification. Pollen and spore ARs also increase prior to Sapropel onset, but a fewcenturies after the increase in marine productivity. Hence, the first shift to a high marine productivity system before Sapropel deposition may have been mostly favoured by the injection of nutrients via shoaling of the nutricline with a minor contributionofnutrientsfromlandviariverinputand floodingoftheshelves.Pollenassemblagesindicatea gradualchangeacrosstheSapropelonsetfromasavanna-like, throughcoastal marshexpansion,towardan open woodland assemblage, which is consistent with enhanced Nile influence and delta development. At Sapropel onset a marked shift in pollen ARs could suggest increased preservation under anoxia. However, major shifts in pollen assemblages and signs of selective- or partial decomposition of terrestrial palynomorphs are absent. We therefore suggest that the high pollen ARs largely result froman increased influx of pollen by enhanced Nile discharge and extension of the freshwater plume. Three centuries after the Sapropel onset, dinocyst ARs and CaCO 3 content indicate that marine productivity starts to decrease, while Sapropeldepositioncontinued.Organiccarboncontentdecreasedonlylaterandlessdramatically.Thismay
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Synchronous basin-wide formation and redox-controlled preservation of a Mediterranean Sapropel
Nature Geoscience, 2008Co-Authors: Gert J. De Lange, John Thomson, Anja Reitz, Caroline P. Slomp, M. Speranza Principato, Elisabetta Erba, C. CorselliAbstract:Organic-rich sedimentary units called Sapropels have formed repeatedly in the eastern Mediterranean Sea, in response to variations of solar radiation. Sapropel formation is due to a change either in the flux of organic matter to the sea floor from productivity changes or in preservation by bottom-water oxygen levels. However, the relative importance of surface-ocean productivity versus deep-water preservation for the formation of these organic-rich shale beds is still being debated, and conflicting interpretations are often invoked1, 2, 3, 4, 5, 6, 7. Here we analyse at high resolution the differences in the composition of the most recent Sapropel, S1, in a suite of cores covering the entire eastern Mediterranean basin. We demonstrate that during the 4,000 years of Sapropel formation, surface-water salinity was reduced and the deep eastern Mediterranean Sea, below 1,800 m depth, was devoid of oxygen. This resulted in the preferential basin-wide preservation of Sapropel S1 with different characteristics above and below 1,800 m depth as a result of different redox conditions. We conclude that climate-induced stratification of the ocean may therefore contribute to enhanced preservation of organic matter in Sapropels and potentially also in black shales.
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Geochemical constraints on Pliocene Sapropel formation in the eastern Mediterranean
Marine Geology, 2000Co-Authors: Ivar A Nijenhuis, Gert J. De LangeAbstract: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 δ 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.
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Modes of Sapropel formation in the eastern Mediterranean: some constraints based on pyrite properties
Marine Geology, 1999Co-Authors: Hilde F. Passier, Jack J. Middelburg, Gert J. De Lange, Michael E. BöttcherAbstract: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. δ34S values of pyrite are −33‰ to −50‰. Below the Sapropels δ34S 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.
Eelco J. Rohling - One of the best experts on this subject based on the ideXlab platform.
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The timing of Mediterranean Sapropel deposition relative to insolation, sea-level and African monsoon changes
Quaternary Science Reviews, 2016Co-Authors: Katharine M Grant, Rosina Grimm, Uwe Mikolajewicz, Gianluca Marino, Martin Ziegler, Eelco J. RohlingAbstract:The Mediterranean basin is sensitive to global sea-level changes and African monsoon variability on orbital timescales. Both of these processes are thought to be important to the deposition of organic-rich sediment layers or ‘Sapropels’ throughout the eastern Mediterranean, yet their relative influences remain ambiguous. A related issue is that an assumed 3-kyr lag between boreal insolation maxima and Sapropel mid-points remains to be tested. Here we present new geochemical and ice-volume-corrected planktonic foraminiferal stable isotope records for Sapropels S1 (Holocene), S3, S4, and S5 (Marine Isotope Stage 5) in core LC21 from the southern Aegean Sea. The records have a radiometrically constrained chronology that has already been synchronised with the Red Sea relative sea-level record, and this allows detailed examination of the timing of Sapropel deposition relative to insolation, sea-level, and African monsoon changes. We find that Sapropel onset was near-synchronous with monsoon run-off into the eastern Mediterranean, but that insolation–Sapropel/monsoon phasings were not systematic through the last glacial cycle. These latter phasings instead appear to relate to sea-level changes. We propose that persistent meltwater discharges into the North Atlantic (e.g., at glacial terminations) modified the timing of Sapropel deposition by delaying the timing of peak African monsoon run-off. These observations may reconcile apparent model–data offsets with respect to the orbital pacing of the African monsoon. Our observations also imply that the previous assumption of a systematic 3-kyr lag between insolation maxima and Sapropel midpoints may lead to overestimated insolation–Sapropel phasings. Finally, we surmise that both sea-level rise and monsoon run-off contributed to surface-water buoyancy changes at times of Sapropel deposition, and their relative influences differed per Sapropel case, depending on their magnitudes. Sea-level rise was clearly important for Sapropel S1, whereas monsoon forcing was more important for Sapropels S3, S4, and S5.
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Mediterranean climate and oceanography, and the periodic development of anoxic events (Sapropels)
Earth-Science Reviews, 2015Co-Authors: Eelco J. Rohling, Gianluca Marino, Katharine M GrantAbstract:Mediterranean Sapropels are layers with elevated organic carbon concentrations that contrast with surrounding sediments, which are organic poor. Sapropels occur (quasi-) periodically in sedimentary sequences of the last 13.5 million years, and exist both in the eastern and western Mediterranean sub-basins. They have been the subject of extensive study, based on records from both short (conventional) and long (Ocean Drilling Program) sediment cores, and from a wide variety of uplifted marine sediment sequences on the basin margins and islands. Previous syntheses in the 1990s and 2000s have discussed how the formation of Sapropels is commonly ascribed to deep-sea anoxia, enhanced export productivity, or a combination of these effects. However, a wealth of new evidence and insights has emerged during the past 1–2 decades, based on traditional and novel proxy data as well as modelling, which has revealed intriguing new aspects and nuances to the reconstructed conditions. Hence, it is timely to present a new synthesis of current understanding of the processes behind the formation of Sapropels, which have over the past decade also become a matter of commercial interest in sub-salt hydrocarbon exploration. In this review, we present a context of modern Mediterranean climate and oceanography, followed by an integrated assessment of the growing understanding of climatological and ocean circulation changes that were associated with Sapropel deposition. We find that Sapropels predominantly formed during (astronomically timed) episodes when climatic and oceanographic conditions and ecological responses broadly preconditioned the basin for Sapropel deposition. There is strong correspondence with times of monsoon intensification, fuelling runoff from North Africa into the Mediterranean Sea, while preconditioning due to sea-level rise, and regional precipitation and runoff may have contributed as well. Within these broad episodes of surface buoyancy gain and resultant decline in deep-water ventilation, specific deposition under dysoxic, anoxic, or even euxinic conditions occurred within a clearly dynamic system that was characterised by complex spatial and depth-dependent patterns/gradients, with distinct temporal variability on (at least) decadal to centennial–millennial timescales. In the final section, we evaluate the implications of different modes of deep-water removal from silled basins, to investigate why Sapropels are more frequently and often more intensely developed in the eastern Mediterranean than in the western Mediterranean.
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abrupt shoaling of the nutricline in response to massive freshwater flooding at the onset of the last interglacial Sapropel event
Paleoceanography, 2012Co-Authors: Michael Grelaud, Gianluca Marino, Patrizia Ziveri, Eelco J. RohlingAbstract:A detailed assessment of the respective roles of production, export, and subsequent preservation of organic carbon (Corg) in the eastern Mediterranean (EMED) sediments during the formation of Sapropels remains elusive. Here we present new micropaleontological results for both surface samples taken at several locations in the EMED and last interglacial Sapropel S5 from core LC21 in the southeastern Aegean Sea. A strong exponential anticorrelation between relative abundances of the lower photic zone coccolithophore Florisphaera profunda in the surface sediments and modern concentrations of chlorophyll a (Chl-a) at the sea surface suggests that F. profunda percentages can be used to track past productivity changes in the EMED. Prior to S5 deposition, an abrupt and large increase of F. profunda percentages in LC21 coincided (within the multidecadal resolution of the records) with the marked freshening of EMED surface waters. This suggests a strong coupling between freshwater-bound surface to intermediate water (density) stratification and enhanced upward advection of nutrients to the base of the photic zone, fuelling a productive deep chlorophyll maximum (DCM) underneath a nutrient-starved surface layer. Our findings imply that (at least) at the onset of Sapropel formation physical and biogeochemical processes likely operated in tandem, enabling high Corg accumulation at the seafloor.
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reconstructing the seafloor environment during Sapropel formation using benthic foraminiferal trace metals stable isotopes and sediment composition
Paleoceanography, 2010Co-Authors: S Ni C Fhlaithearta, Gert-jan Reichart, Eelco J. Rohling, John Thomson, Christophe Fontanier, Frans Jorissen, G. J. De LangeAbstract:The evolution of productivity, redox conditions, temperature, and ventilation during the deposition of an Aegean Sapropel (S1) is independently constrained using bulk sediment composition and high-resolution single specimen benthic foraminiferal trace metal and stable isotope data. The occurrence of benthic foraminifer, Hoeglundina elegans (H. elegans), through a shallow water (260 m) Sapropel, permits for the first time a comparison between dissolved and particulate concentrations of Ba and Mn and the construction of a Mg/Ca–based temperature record through Sapropel S1. The simultaneous increase in sedimentary Ba and incorporated Ba in foraminiferal test carbonate, (Ba/Ca)H. elegans, points to a close coupling between Ba cycling and export productivity. During Sapropel deposition, sedimentary Mn content ((Mn/Al)sed) is reduced, corresponding to enhanced Mn2+ mobilization from sedimentary Mn oxides under suboxic conditions. The consequently elevated dissolved Mn2+ concentrations are reflected in enhanced (Mn/Ca)H. elegans levels. The magnitude and duration of the Sapropel interruption and other short-term cooling events are constrained using Mg/Ca thermometry. Based on integrating productivity and ventilation records with the temperature record, we propose a two-mode hysteresis model for Sapropel formation.
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hydrogen isotopic compositions of long chain alkenones record freshwater flooding of the eastern mediterranean at the onset of Sapropel deposition
Earth and Planetary Science Letters, 2007Co-Authors: Eelco J. Rohling, Gianluca Marino, Marianne Baas, Marcel T J Van Der Meer, Irene W C Rijpstra, Jaap Sinninghe S DamsteAbstract:Sapropels are organic-rich sediment layers that were intermittently deposited in the Mediterranean Sea, especially in its eastern basin, during the last 10Myr. The associated anoxic events that gave rise to Sapropel formation resulted indirectly from the impact of African monsoon maxima on the basin's hydrography. Sharp shifts in oxygen isotopes (?18O) to values more depleted in the heavy isotope (18O) in carbonates from surface dwelling planktonic foraminifera, slightly preceding Sapropel deposition, suggest that the Mediterranean was flooded by large amounts of freshwater leading to the development of a low salinity of the surface water and a strong density stratification of the water column. However, the degree of freshwater flooding and concomitant drop in sea surface salinity (SSS) remain elusive. Recent work has shown that the hydrogen isotope (?D) values of long-chain alkenones produced by haptophyte algae depend mainly on the ?D of the water and on salinity, and may therefore offer a new tool for salinity reconstructions. Our analysis of the ?D of alkenones from last interglacial Sapropel S5 from the Aegean Sea shows a large decrease in ?D of 25‰ at the onset of Sapropel formation, suggesting a drop in SSS of 6, from 39 to 33. Although the absolute SSS estimates should be interpreted with care as they are subject to relatively large uncertainties, the estimated SSS values appear quite reasonable as they, for example, yield SSS before Sapropel deposition similar to that of the present day Aegean Sea. To reduce uncertainties in SSS estimates, the ?D-salinity relationship has to be better constrained with cultures and also tested in field studies. However, our results do illustrate the promise of a combined use of ?D of alkenones, U37k? of alkenones, and ?18O of surface dwelling planktonic foraminifera, for SSS reconstructions.
G. J. De Lange - One of the best experts on this subject based on the ideXlab platform.
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evaluation and application of foraminiferal element calcium ratios assessing riverine fluxes and environmental conditions during Sapropel s1 in the southeastern mediterranean
Marine Micropaleontology, 2019Co-Authors: Meryem Mojtahid, Rick Hennekam, Gert-jan Reichart, L J De Nooijer, F J Jorissen, Wim Boer, Le S Houedec, G. J. De LangeAbstract:Abstract Paleostudies often rely on foraminiferal calcite chemistry, which reflect past sea water condition through so-called proxy relationships. One way to evaluate robustness of these proxy relationships is to test them in well-studied and during well-constrained climate transitions. The southeastern (SE) Mediterranean is a perfect natural laboratory with a large range of past environmental conditions. These range from low productivity well-ventilated waters like they are at present, to poorly ventilated, high productivity conditions during Sapropels. We here explore the reliability of recently developed foraminiferal-based proxies (Ba/Ca, Mn/Ca, Na/Ca) as tracers for changes in productivity, oxygenation and salinity during the most recent Sapropel S1. We use laser ablation ICP-MS analyses of the planktonic G. ruber and six benthic species (B. alata, G. affinis, G. altiformis, G. orbicularis, H. boueana, U. peregrina). Our results show that planktonic Ba/Ca is a reliable tracer for Ba2+-enriched Nile outflow, where benthic Ba/Ca traces enhanced paleo(export) productivity relatively well. The interpretation of Mn/Ca data is less straightforward, and the low values may suggest a lower precipitation of Mn-oxides under prevailing hypoxia. The decrease in planktonic and benthic Na/Ca is coherent with excess Nile runoff lowering salinities in the
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eastern mediterranean ventilation variability during Sapropel s1 formation evaluated at two sites influenced by deep water formation from adriatic and aegean seas
Quaternary Science Reviews, 2016Co-Authors: Amalia Filippidi, Maria Triantaphyllou, G. J. De LangeAbstract:Abstract Present-day bottom-water ventilation in the Eastern Mediterranean basin occurs through deep-water convection originating from the two marginal basins, i.e. Adriatic and Aegean Seas. In the paleo record, long periods of enhanced deep-water formation have been alternating with shorter periods of reduced deep-water formation. The latter is related mainly to low-latitude humid climate conditions and the enhanced deposition and preservation of organic-rich sediment units (Sapropels). This study focuses on sedimentary archives of the most-recent Sapropel S1, retrieved from two sites under the direct influence of the two deep-water formation areas. Restricted oxygen conditions have developed rapidly at the beginning of S1 deposition in the Adriatic site, but bottom-water conditions have not persistently remained anoxic during the full interval of Sapropel deposition. In fact, the variability in intensity and persistence of sedimentary redox conditions at the two deep-water formation sites is shown to be related to brief episodes of climate cooling. In the Adriatic site, Sapropel deposition appears to have been interrupted twice. The 8.2 ka event, only recovered at the Adria site, is characterized by gradually increasing suboxic to possibly intermittently oxic conditions and decreasing C org fluxes, followed by an abrupt re-establishment of anoxic conditions. Another important event that disrupted Sapropel S1 formation, has taken place at ca. 7.4 cal ka BP. The latter event has been recovered at both sites. In the Adriatic site it is followed by a period of sedimentary conditions that gradually change from suboxic to more permanently oxic, as deduced from the Mn/Al pattern. Using the same proxy for suboxic/oxic sedimentary redox conditions, we observe that conditions in the Aegean Sea site shift to more permanently oxic from the 7.4 ka event onwards. However, at both sites the accumulation and preservation of enhanced amounts of organic matter have continued under these suboxic to intermittently oxic sedimentary conditions. It seems thus, that after 7.4 cal ka BP Sapropel-like surface or deep-chlorophyll-maximum conditions including enhanced productivity continued, whereas bottom-water conditions were at least intermittently oxic. The latter is related to decreasing precipitation, i.e. run-off, and thus a progressive development and deepening of deep-water formation. The shallower Aegean site, would be affected earlier by such deepening ventilation than the slightly deeper Adriatic site. Finally, termination of Sapropel S1 formation as deduced from diminished organic matter contents and Ba/Al, appears to have occurred almost simultaneously in the two areas, namely at 6.6 ± 0.3 and 6.3 ± 0.5 cal ka BP in Adriatic and Aegean sites, respectively.
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reconstructing the seafloor environment during Sapropel formation using benthic foraminiferal trace metals stable isotopes and sediment composition
Paleoceanography, 2010Co-Authors: S Ni C Fhlaithearta, Gert-jan Reichart, Eelco J. Rohling, John Thomson, Christophe Fontanier, Frans Jorissen, G. J. De LangeAbstract:The evolution of productivity, redox conditions, temperature, and ventilation during the deposition of an Aegean Sapropel (S1) is independently constrained using bulk sediment composition and high-resolution single specimen benthic foraminiferal trace metal and stable isotope data. The occurrence of benthic foraminifer, Hoeglundina elegans (H. elegans), through a shallow water (260 m) Sapropel, permits for the first time a comparison between dissolved and particulate concentrations of Ba and Mn and the construction of a Mg/Ca–based temperature record through Sapropel S1. The simultaneous increase in sedimentary Ba and incorporated Ba in foraminiferal test carbonate, (Ba/Ca)H. elegans, points to a close coupling between Ba cycling and export productivity. During Sapropel deposition, sedimentary Mn content ((Mn/Al)sed) is reduced, corresponding to enhanced Mn2+ mobilization from sedimentary Mn oxides under suboxic conditions. The consequently elevated dissolved Mn2+ concentrations are reflected in enhanced (Mn/Ca)H. elegans levels. The magnitude and duration of the Sapropel interruption and other short-term cooling events are constrained using Mg/Ca thermometry. Based on integrating productivity and ventilation records with the temperature record, we propose a two-mode hysteresis model for Sapropel formation.
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florisphaera profunda and the origin and diagenesis of carbonate phases in eastern mediterranean Sapropel units
Paleoceanography, 2004Co-Authors: J Thomson, G. J. De Lange, Caroline P. Slomp, Elisabetta Erba, C. Corselli, D Crudeli, S E CalvertAbstract:High relative concentrations of the lower photic zone nannofossil Florisphaera profunda have been reported in all recent eastern Mediterranean Sapropels. In the most recent Sapropel (S1), high bulk sediment Sr/Ca ratios occur along with high F. profunda contents toward the base of the unit, exemplified here in four cores from 1.5–3.5 km water depth. Co-occurring biogenic carbonates contain insufficient Sr to account for these high Sr concentrations, and X-ray diffraction and selective leaching show that the high Sr/Ca ratios are due to aragonite, the CaCO3 polymorph that is rarely preserved in deep marine sediments, with ∼1 wt % Sr. The possible sources of this aragonite include (1) precipitation with surface ocean production, (2) detrital input from shallow-water sediments by high continental runoff, or (3) postdepositional diagenetic formation driven by increased pore water alkalinity resulting from sulphate reduction. The third formation mechanism for the aragonite is favored, in which case the similarity in the positions of the aragonite and F. profunda abundance maxima in Sapropels is probably related to Corg accumulation and resulting sulphide diagenesis that produces high pore water alkalinity. There is clear micropaleontological evidence that dissolution of the less soluble biogenic low-Mg CaCO3 is occurring, or has occurred, during early diagenesis in these sediments despite the coexistence of the more soluble high-Mg calcite and aragonite polymorphs. Similar Sr/Ca maxima are also found associated with older Sapropels, always located close both to local minima in surface ocean δ18O that signal maximum monsoon-driven runoff and to maxima in diagenetic sediment sulphide contents. High freshwater flows from monsoons are believed to drive eastern Mediterranean Sapropel formation through water column stabilization that favors F. profunda production and later through development of deep water column dysoxia/anoxia because of reduced ventilation. The relative abundances of F. profunda are high between 5 and 11 14C kyr B.P. with a maximum at ∼9 14C kyr B.P. The surface ocean production changes marked by F. profunda therefore begin earlier and finish later than the formation of the S1 Sapropel, which only develops between 6 and 10 14C kyr B.P.
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magnetic properties and geochemistry of the active oxidation front and the youngest Sapropel in the eastern mediterranean sea
Geophysical Journal International, 2001Co-Authors: Hilde F. Passier, G. J. De Lange, Mark J. DekkersAbstract: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.
Kay-christian Emeis - One of the best experts on this subject based on the ideXlab platform.
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Late glacial initiation of Holocene eastern Mediterranean Sapropel formation.
Nature communications, 2015Co-Authors: Rosina Grimm, Gerhard Schmiedl, Katharine M Grant, Uwe Mikolajewicz, Martin Ziegler, Ernst Maier-reimer, Katharina Müller-navarra, Fanny Adloff, Lucas Joost Lourens, Kay-christian EmeisAbstract:Recurrent deposition of organic-rich sediment layers (Sapropels) in the eastern Mediterranean Sea is caused by complex interactions between climatic and biogeochemical processes. Disentangling these influences is therefore important for Mediterranean palaeo-studies in particular, and for understanding ocean feedback processes in general. Crucially, Sapropels are diagnostic of anoxic deep-water phases, which have been attributed to deep-water stagnation, enhanced biological production or both. Here we use an ocean-biogeochemical model to test the effects of commonly proposed climatic and biogeochemical causes for Sapropel S1. Our results indicate that deep-water anoxia requires a long prelude of deep-water stagnation, with no particularly strong eutrophication. The model-derived time frame agrees with foraminiferal δ(13)C records that imply cessation of deep-water renewal from at least Heinrich event 1 to the early Holocene. The simulated low particulate organic carbon burial flux agrees with pre-Sapropel reconstructions. Our results offer a mechanistic explanation of glacial-interglacial influence on Sapropel formation.
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reconstructing past planktic foraminiferal habitats using stable isotope data a case history for mediterranean Sapropel s5
Marine Micropaleontology, 2004Co-Authors: Eelco J. Rohling, Kay-christian Emeis, Ioanna Bouloubassi, Mario Sprovieri, T R Cane, J S L Casford, S Cooke, Ralf Schiebel, Mike Rogerson, Angela HayesAbstract:Abstract A high-resolution stable O and C isotope study is undertaken on all planktic foraminiferal species that are reasonably continuous through an Eemian Sapropel S5 from the western side of the eastern Mediterranean. The data are considered within a context of high-resolution isotope records for two further S5 Sapropels from the central and easternmost sectors of the basin, alkenone-based sea surface temperature records for all three Sapropels, and planktic foraminiferal abundance records for the same sample sets through all three Sapropels. Results are compared with similar data for Holocene Sapropel S1. The adopted approach allows distinction between species that are most suitable to assess overall changes in the climatic/hydrographic state of the basin, including depth-related differentiations and the main seasonal developments, and species that are most affected by variable biological controls or local/regional and transient physico–chemical forcings. It is found that a-priori assumptions about certain species’ palaeohabitats, based on modern habitat observations, may become biased when non-analogue conditions develop. In the case of Mediterranean Sapropel S5, these consisted of enhanced freshwater dilution, elevated productivity, shoaling of the pycnocline between intermediate and surface waters, and stagnation of the subsurface circulation. Under these conditions, some species are found to ‘shift’ into habitat settings that differ considerably from those occupied today. The present multiple-species approach can identify such ‘anomalous responses’, and thus offers a sound background for further shell-chemistry investigations and quantitative interpretation of the isotopic profiles. We capitalise on the latter potential, and offer the first quantitative estimates of monsoon flooding into the Mediterranean during the deposition of Eemian Sapropel S5.
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benthic foraminiferal record of ecosystem variability in the eastern mediterranean sea during times of Sapropel s5 and s6 deposition
Palaeogeography Palaeoclimatology Palaeoecology, 2003Co-Authors: Gerhard Schmiedl, Angelika Mitschele, Kay-christian Emeis, Christoph Hemleben, Hartmut Schulz, Michael R Sperling, Stefan Beck, Syee WeldeabAbstract:High-resolution benthic foraminiferal and geochemical investigations were carried out across Sapropels S5 and S6 from two sediment cores in the Levantine Sea to evaluate the impact of climatic and environmental changes on benthic ecosystems during times of Sapropel formation. The faunal successions indicate that eutrophication and/or oxygen reduction started several thousand years prior to the onset of Sapropel formation, suggesting an early response of the bathyal ecosystems to climatic changes. Severest oxygen depletions appear in the early phases of Sapropel formation. The initial reduction of deep-water ventilation is caused by a warming and fresh water-induced stratification of Eastern Mediterranean surface waters. During the late phase of S5 formation improved oxygenation is restricted to middle bathyal ecosystems, indicating that at least some formation of subsurface water took place. During S6 formation oxygen depletions and eutrophication were less severe and more variable than during S5 formation. Estimated oxygen contents were low dysoxic at middle bathyal to anoxic at lower bathyal depths during the early phase of S6 formation but never dropped to anoxic values in its late phase. The high benthic ecosystem variability during S6 formation suggests that water column stratification at deep-water formation sites was in a very unstable mode and susceptible to minor temperature fluctuations at a millennial time-scale. 5 2002 Elsevier Science B.V. All rights reserved.
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benthic foraminiferal record of ecosystem variability in the eastern mediterranean sea during times of Sapropel s5 and s6 deposition
Palaeogeography Palaeoclimatology Palaeoecology, 2003Co-Authors: Gerhard Schmiedl, Angelika Mitschele, Kay-christian Emeis, Christoph Hemleben, Hartmut Schulz, Michael R Sperling, Stefan Beck, Syee WeldeabAbstract:Abstract High-resolution benthic foraminiferal and geochemical investigations were carried out across Sapropels S5 and S6 from two sediment cores in the Levantine Sea to evaluate the impact of climatic and environmental changes on benthic ecosystems during times of Sapropel formation. The faunal successions indicate that eutrophication and/or oxygen reduction started several thousand years prior to the onset of Sapropel formation, suggesting an early response of the bathyal ecosystems to climatic changes. Severest oxygen depletions appear in the early phases of Sapropel formation. The initial reduction of deep-water ventilation is caused by a warming and fresh water-induced stratification of Eastern Mediterranean surface waters. During the late phase of S5 formation improved oxygenation is restricted to middle bathyal ecosystems, indicating that at least some formation of subsurface water took place. During S6 formation oxygen depletions and eutrophication were less severe and more variable than during S5 formation. Estimated oxygen contents were low dysoxic at middle bathyal to anoxic at lower bathyal depths during the early phase of S6 formation but never dropped to anoxic values in its late phase. The high benthic ecosystem variability during S6 formation suggests that water column stratification at deep-water formation sites was in a very unstable mode and susceptible to minor temperature fluctuations at a millennial time-scale.
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the Sapropel record of the eastern mediterranean sea results of ocean drilling program leg 160
Palaeogeography Palaeoclimatology Palaeoecology, 2000Co-Authors: Kay-christian Emeis, Rolf Wehausen, Tatsuhiko Sakamoto, Hans-jürgen BrumsackAbstract:Research on sediments recovered during Ocean Drilling Leg 160 has concentrated on two issues: the first concerned the stratigraphy of Sapropel formation, the second was oriented to clarify specific processes that explain Sapropel origin. Progress has been made in the construction of stratigraphic composites out of sedimentary sequences from individual holes at each of the palaeoceanographic sites. On the composites, initial work has resulted in the establishment of high-resolution and intermediate-resolution stratigraphies for three sites (963, 964, 967); correlation of sedimentary cycles to astronomical (insolation) cycles extends the stratigraphies to Sites 969 and 966. The Sapropel occurrences in the marine and land sequences over the entire Eastern Mediterranean are correlated; with the resolution that can be obtained from isotope studies, groups of Sapropels occurred simultaneously over the entire basin. In detail, however, the temporal and facies patterns of Sapropel sequences differ between individual sites and depositional basins. The differences may be related to effects of water depth, diagenesis, and post-depositional tectonic attenuation of sequences. Studies on the geochemistry and facies of Sapropels agree that anoxic conditions favoured preservation of organic matter in Sapropels, caused the enrichment of trace metals associated with Sapropels, and helped to preserve primary sedimentary structures. Besides, all evidence is consistent with elevated fluxes of organic matter and associated elements during Sapropel events.
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florisphaera profunda and the origin and diagenesis of carbonate phases in eastern mediterranean Sapropel units
Paleoceanography, 2004Co-Authors: J Thomson, G. J. De Lange, Caroline P. Slomp, Elisabetta Erba, C. Corselli, D Crudeli, S E CalvertAbstract:High relative concentrations of the lower photic zone nannofossil Florisphaera profunda have been reported in all recent eastern Mediterranean Sapropels. In the most recent Sapropel (S1), high bulk sediment Sr/Ca ratios occur along with high F. profunda contents toward the base of the unit, exemplified here in four cores from 1.5–3.5 km water depth. Co-occurring biogenic carbonates contain insufficient Sr to account for these high Sr concentrations, and X-ray diffraction and selective leaching show that the high Sr/Ca ratios are due to aragonite, the CaCO3 polymorph that is rarely preserved in deep marine sediments, with ∼1 wt % Sr. The possible sources of this aragonite include (1) precipitation with surface ocean production, (2) detrital input from shallow-water sediments by high continental runoff, or (3) postdepositional diagenetic formation driven by increased pore water alkalinity resulting from sulphate reduction. The third formation mechanism for the aragonite is favored, in which case the similarity in the positions of the aragonite and F. profunda abundance maxima in Sapropels is probably related to Corg accumulation and resulting sulphide diagenesis that produces high pore water alkalinity. There is clear micropaleontological evidence that dissolution of the less soluble biogenic low-Mg CaCO3 is occurring, or has occurred, during early diagenesis in these sediments despite the coexistence of the more soluble high-Mg calcite and aragonite polymorphs. Similar Sr/Ca maxima are also found associated with older Sapropels, always located close both to local minima in surface ocean δ18O that signal maximum monsoon-driven runoff and to maxima in diagenetic sediment sulphide contents. High freshwater flows from monsoons are believed to drive eastern Mediterranean Sapropel formation through water column stabilization that favors F. profunda production and later through development of deep water column dysoxia/anoxia because of reduced ventilation. The relative abundances of F. profunda are high between 5 and 11 14C kyr B.P. with a maximum at ∼9 14C kyr B.P. The surface ocean production changes marked by F. profunda therefore begin earlier and finish later than the formation of the S1 Sapropel, which only develops between 6 and 10 14C kyr B.P.
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a dynamic concept for eastern mediterranean circulation and oxygenation during Sapropel formation
Palaeogeography Palaeoclimatology Palaeoecology, 2003Co-Authors: J S L Casford, Gerhard Schmiedl, Eelco J. Rohling, Ramadan H Abuzied, Christophe Fontanier, Frans Jorissen, Melanie J Leng, J ThomsonAbstract:We propose that intermittent bottom water ventilation occurred throughout periods of Sapropel deposition, and that the recently reported Sapropel ‘interruptions’ represent centennial-scale episodes of enhanced frequency/intensity of that process. In essence, the modern high-frequency variability in deep water formation (affected by climatic variability over the northern basins on seasonal to longer time scales) prevailed also at times of Sapropel deposition, although the overall ventilation state was much reduced. This concept is supported by: detailed multiple-species isotope records for three Aegean cores; the presence of abundant Globorotalia truncatulinoides within especially Sapropels S7 and S8 in the western Levantine basin; observations of three rapid benthic repopulations within Sapropel S6 in the deep western Levantine basin; a report of continuous benthic presence through Sapropel S1 at intermediate-deep locations offshore Libya; and further supporting information from the literature. In the Aegean records, concomitant abundance of low-oxygen tolerant benthic foraminifera and presence of the more oxyphilic benthic foraminifer Uvigerina mediterranea, with surface-similar δ13C values, indicate repeated deep water re-oxygenation events throughout the deposition of S1. The observations of a continuous benthic presence through S1 (offshore from Libya) imply that no persistent anoxia developed at mid-depth levels in that region, which is far removed from direct deep ventilation influences. The abundance of deep mesopelagic G. truncatulinoides through several Sapropels from the western Levantine basin also suggests the presence of bio-available oxygen at many hundreds of meters of depth. Moreover, the rapid/intermittent benthic repopulations within Sapropels from the deep eastern Mediterranean imply that bottom water anoxia was spatially restricted and/or of a highly intermittent nature. The short time scales of these repopulation events are incompatible with titration of an extensively anoxic water column and subsequent re-establishment of water-column anoxia. We suggest that where anoxic/azoic conditions were present, they most likely were restricted to a veneer at the sediment/water interface. The extent of such an anoxic ‘blanket’ depends on the balance between advective oxygen supply into the deep sea, and biological and chemical oxygen demand. The demand functions imply a decoupling of oxygenation from water mass advection, allowing export production and Corg posting rates to the sea floor to delimit the extent of the anoxic blanket in both space and time. Low-productivity regions would develop no anoxic blanket, allowing for the observed persistence of deep dwelling planktonic and bottom dwelling benthic faunas.
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high resolution geochemical and micropalaeontological profiling of the most recent eastern mediterranean Sapropel
Marine Geology, 2001Co-Authors: D Mercone, Ramadan H Abuzied, Ian W. Croudace, J Thomson, Eelco J. RohlingAbstract: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.
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review of recent advances in the interpretation of eastern mediterranean Sapropel s1 from geochemical evidence
Marine Geology, 1999Co-Authors: J Thomson, G. J. De Lange, D Mercone, P J M Van SantvoortAbstract:Abstract The sediments of the eastern Mediterranean basin contain C org -enriched layers (Sapropels) interbedded with the C org -poor sediments which form by far the greater part of the record. While it is generally appreciated that different surface ocean productivity and bottom water conditions are necessary for the formation and preservation of these two sediment types, less attention has been paid to diagenetic effects which are an expected consequence of transitions between dramatically different bottom water oxygenation levels. A geochemical interpretation has emerged of post-depositional oxidation of the most recent Sapropel (S1), initially based on the relationship of the Mn, Fe, C org and S concentration/depth profiles observed around S1, and the characteristic shapes of these elemental profiles known from other situations. This indicates that post-depositional oxidation has removed approximately half of the visual evidence of the Sapropel (∼6 cm from a total of ∼12 cm in the deep basin). The oxidation interpretation from redox-sensitive element redistribution profiles has subsequently been consolidated with evidence from pore water (O 2 , NO − 3 , Mn 2+ and Fe 2+ ) studies, from characteristic solid phase Ba profiles which yield palaeoproductivity records, and from oxidation-sensitive indicator trace elements (I and Se). So far, these geochemical observations have been concentrated in the deeper central parts of the basin, where sediment accumulation rates are lower than on the basin margins, and radiocarbon dating indicates that S1 formation occurred between 5.3 and 9.0 ky (uncorrected conventional radiocarbon time). It remains to be demonstrated whether or not these times are applicable to the entire E. Mediterranean basin. The implications of these findings to guide sampling in future work on the S1 productivity episode and on older Sapropels for palaeoenvironmental investigations are discussed.
