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In marine sediments, the Sr content and isotope composition (87Sr/86Sr) of the terrigenous detrital component are widely used to track changes in provenance and related transport and weathering processes. Accurately separating detrital-Sr from other sedimentary Sr-phases is a prerequisite for such studies. Conventionally, it is assumed that Sr in the carbonate-free residue corresponds to detrital Sr alone. However, the decarbonated residue may contain barite with significant Sr content and a non-detrital 87Sr/86Sr composition; this may substantially affect the measured Sr signal. To examine this chronically overlooked phenomenon, the Mediterranean Sea is an ideal area because 1) detailed provenance studies have been done using Sr and 87Sr/86Sr of the residual fraction, and 2) enhanced levels of barite repeatedly occurred in association with distinct, organic-rich sapropel sediments. Here, we use the most-recent sapropel S1 interval to evaluate the effect of barite-bound Sr in the residual fraction after decarbonation. A total of 130 samples were taken from 10 cores in the eastern Mediterranean Sea (EMS) and 1 core in the western Mediterranean Sea. This selection represents a geographic and bathymetric coverage of the EMS and permits the basin-wide comparison between organic-rich and -lean sediments. After decarbonation using 1 M HCl solution, the residual sediments were subject to NH 4 Cl extraction (2 M, pH 7), known to selectively dissolve barite. Our results demonstrate the presence of Sr-bearing barite after traditional carbonate removal and its effect on the derived "detrital" Sr signature. This barite-Sr effect is considerable for samples with barite-Ba >400 μg/g in bulk sediment. The impact of barite is prominent if accompanied by a detrital provenance background of high 87Sr/86Sr (>0.713) or low Sr/Al (<1.0 mg/g). In such cases, removal of remaining barite is required to obtain an unbiased detrital Sr signal. We recommend an improved procedure for detrital Sr separation in marine sediments, with an additional NH 4 Cl leaching step to eliminate any remaining barite after decarbonation. This approach is particularly important for areas/times of high biological productivity, where sediments are often characterized by abundant barite content. • Sr-bearing barite remains after traditional decarbonation. • Such remaining barite-Sr may affect detrital Sr isotope systematics. • Pertinent examples from 11 Mediterranean basin-wide cores are used for illustration. • Adequate method is provided to improve detrital Sr separation in marine sediments. [ABSTRACT FROM AUTHOR]

Abstract: Suboxic sapropel S1 sediments of the eastern Mediterranean carry an untypically light δ 98/95Mo signal, being even lighter than oxic Mn-enriched sediments and Mn-crusts/nodules, which were previously thought to carry the lightest Mo isotope values. The evaluation and comparison of oxic S1, diagenetically overprinted oxic S1, and suboxic S1 sediments indicates that this light isotope signal is primarily an oxic signal that has been overprinted by secondary diagenetic processes occurring after sediment burial. Such secondary processes bear the potential of additional Mo isotope fractionation in particular in non-steady state diagenetic environments that involve the discontinuous re-location of the redox boundary. [Copyright &y& Elsevier]

Abstract: The Holocene–late Pleistocene distribution of holococcoliths, is quantified by light microscopy from cores from the Western Mediterranean, the Aegean Sea and eight eastern Mediterranean cores recovering sapropel S1. The diversity of fossil holococcoliths is much lower than is seen in the plankton, indicating selective preservation. However the holococcolith phases of Syracosphaera pulchra and Helicosphaera carteri are abundantly preserved allowing a comparison of fossil records of heterococcolith and holococcolith phases of these species. In shallow cores a primary palaeocological signal appears to be preserved, suggesting that under suitable circumstances it is possible to use holococcoliths in palaeoceanography. The common occurrence of holococcoliths in the sapropels from these cores suggests low surface-water productivity, supporting previous inferences that productivity enhancement during sapropel deposition was confined to the deep-chlorophyll maximum. In deeper cores there is dramatic decrease in abundance of S. pulchra holococcoliths within sapropel sediments. From comparison of shallow and deep cores and from Emiliania huxleyi preservation data we conclude that this is a preservation signal. Evidently the calyptroliths produced by S. pulchra have a lower preservation potential than the syracoliths produced by H. carteri, we interpret this as a product of their more open structure. [Copyright &y& Elsevier]

The chemical composition of the Bannock basin has been studied in some detail. We recently showed that unusual microbial populations, including a new division of Archaea (MSBL1), inhabit the NaCl-rich hypersaline brine. High salinities tend to reduce biodiversity, but when brines come into contact with fresher water the natural haloclines formed frequently contain gradients of other chemicals, including permutations of electron donors and acceptors, that may enhance microbial diversity, activity and biogeochemical cycling. Here we report a 2.5-m-thick chemocline with a steep NaCl gradient at 3.3 km within the water column betweeen Bannock anoxic hypersaline brine and overlying sea water. The chemocline supports some of the most biomass-rich and active microbial communities in the deep sea, dominated by Bacteria rather than Archaea, and including four major new divisions of Bacteria. Significantly higher metabolic activities were measured in the chemocline than in the overlying sea water and underlying brine; functional analyses indicate that a range of biological processes is likely to occur in the chemocline. Many prokaryotic taxa, including the phylogenetically new groups, were confined to defined salinities, and collectively formed a diverse, sharply stratified, deep-sea ecosystem with sufficient biomass to potentially contribute to organic geological deposits. [ABSTRACT FROM AUTHOR]

Clarification of the factors involved in the formation of unusual ancient organic carbon-rich deposits (like eastern Mediterranean sapropels) is central in understanding oceanic carbon cycling. The role of oxygenation remains a subject of controversy primarily due to two major uncertainties: (1) it is unknown if ancient organic-rich deposits reflect an accumulation of refractory organic matter (OM) or oxygenation-related aberrant sediment OM recycling, and (2) although marine OM degradation may be slower under anoxic conditions, its ultimate impact on organic carbon (Corg) preservation over geological time remains unclear. Here we provide direct experimental evidence that the Corg in eastern Mediterranean S1 sapropels (deposited >5 ka) is still highly reactive and that a shutdown in labile organic matter degradation under anoxic conditions played a key role in the formation of these deposits. [ABSTRACT FROM AUTHOR]

To extend the knowledge of anaerobic ammonium oxidation (anammox) habitats, bacterial communities were examined in two hypersaline sulphidic basins in Eastern Mediterranean Sea. The 2 m thick seawater-brine haloclines of the deep anoxic hypersaline basins Bannock and L'Atalante were sampled in intervals of 10 cm with increasing salinity. (15)N isotope pairing incubation experiments showed the production of (29)N2 and (30)N2 gases in the chemoclines, ranging from 6.0 to 9.2 % salinity of the L'Atalante basin. Potential anammox rates ranged from 2.52 to 49.65 nmol N2 L(-1) day(-1) while denitrification was a major N2 production pathway, accounting for more than 85.5 % of total N2 production. Anammox-related 16S rRNA genes were detected along the L'Atalante and Bannock haloclines up to 24 % salinity, and the amplification of the hydrazine synthase genes (hzsA) further confirmed the presence of anammox bacteria in Bannock. Fluorescence in situ hybridisation and sequence analysis of 16S rRNA genes identified representatives of the marine anammox genus 'Candidatus Scalindua' and putatively new operational taxonomic units closely affiliated to sequences retrieved in marine environments that have documented anammox activity. 'Scalindua brodae' like sequences constituted up to 84.4 % of the sequences retrieved from Bannock. The anammox community in L'Atalante was different than in Bannock and was stratified according to salinity increase. This study putatively extends anammox bacterial habitats to extremely saline sulphidic ecosystems.

We investigated the top 30-cm sediment prokaryotic community structure in 5-cm spatial resolution, at an active site of the Amsterdam mud volcano, East Mediterranean Sea, based on the 16S rRNA gene diversity. A total of 339 and 526 sequences were retrieved, corresponding to 25 and 213 unique (≥98% similarity) phylotypes of Archaea and Bacteria, respectively, in all depths. The Shannon-Wiener diversity index H was higher for Bacteria (1.92-4.03) than for Archaea (0.99-1.91) and varied differently between the two groups. Archaea were dominated by anaerobic methanotrophs ANME-1, -2 and -3 groups and were related to phylotypes involved in anaerobic oxidation of methane from similar habitats. The much more complex Bacteria community consisted of 20 phylogenetic groups at the phylum/candidate division level. Proteobacteria, in particular δ-Proteobacteria, was the dominant group. In most sediment layers, the dominant phylotypes of both the Archaea and Bacteria communities were found in neighbouring layers, suggesting some overlap in species richness. The similarity of certain prokaryotic communities was also depicted by using four different similarity indices. The direct comparison of the retrieved phylotypes with those from the Kazan mud volcano of the same field revealed that 40.0% of the Archaea and 16.9% of the Bacteria phylotypes are common between the two systems. The majority of these phylotypes are closely related to phylotypes originating from other mud volcanoes, implying a degree of endemicity in these systems.