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The Neogene Lake Pannon was the largest lake that ever existed in Europe. It attained its greatest extent during the Tortonian Thermal Maximum. For the first time, results from a detailed lake record documenting about 85 kyr of Late Miocene time in a continuously recovered, 60-m-long, clay-rich core of Lake Pannon are reported. This record includes the transition from the lake's maximum transgression into its highstand at around 10.4 Ma. The environmental development of Lake Pannon during its maximum extent is interpreted based on integrated paleontological, sedimentological, mineralogical and geochemical data. The maximum extent coincided with stable sedimentation of clay, little influx from the hinterland, low surface productivity and severe bottom-water anoxia. The clay mineralogy of the lower part of the core points to prevailing chemical weathering based on the illite/smectite ratios. Distinct Fe, Mn and Ba enrichments are interpreted to have formed close to sulfate-methane transition zones during the maximum flooding. The highstand phase was marked by rapid environmental shifts with frequent phases of well‑oxygenated bottom waters. These phases are reflected by rich benthic communities including stenohaline tunicates. The increased input of detritic kaolinite suggests a shift towards physical weathering and higher precipitation coinciding with a shift in the provenance of clay minerals. Increasing amounts of nutrients stimulated surface water productivity and nannoplankton blooms. Despite the offshore position of the core at ∼8 km from the mountainous ranges of the Alps, strong fluvial input is reflected from 32.5 to 30.3 m by coarser sediment and the occurrence of terrestrial and freshwater molluscs. The Rhenodanubian Flysch Unit was the main source of the siliciclastics of the core and was drained by the Paleo-Wien river. Drainage from the Calcareous Alps was limited to an exceptionally strong fluvial event and related deposits, which documents the presence of a second river in the southwest, which might represent the Paleo-Liesing. The dominance of smectite throughout the core suggests a temperate climate with distinct seasonality during the Tortonian Thermal Maximum. In view of the autochthonous ascidian sclerites in three samples, and assuming generally similar ecological requirements for both Pannonian and modern tunicates, we conclude a polyhaline salinity for Lake Pannon around 10.4 Ma.

The deposition of Organic-Rich Layers (ORLs) and sapropels in the Mediterranean Sea basins represents an exceptional record of severe changes in oxygenation over the recent geological past. Such changes are also associated to rapid productivity oscillations that involved a major increase in export fluxes of organic carbon. These episodes of enhanced production and preservation of organic matter can be used as a natural archive for studying oxygen fluctuations and deoxygenation events, and a better comprehension of the causes and consequences of past events will provide valuable information to further understand oxygen level variations in future scenarios. In general, sapropel deposition has been related to increased productivity and sluggish water circulation in response to African monsoon variability. To further understand how such conditions led to bottom water oxygen depletion, a multiproxy approach, including diverse geochemical and ichnological proxies, has been applied. Obtained results have provided new insights into the relationship between productivity and oxygen conditions in the water column and at the sediment-water interface. Sapropels intervals from cores recovered at four ODP Leg 160 sites were selected across an East-West transect of the Eastern Mediterranean basin entailing diverse depths and oceanographic regimes. At these sites, sapropel layers had been well characterized in terms of productivity (i.e. Ba/Al and TOC), and new analyses have been performed to provide additional redox proxies, i.e. degree of pyritization (DOP), trace elements ratios, and enrichment factors (EF) that have allowed a high-resolution reconstruction of bottom-water ventilation. Also, a preliminary ichnological approach is coupled with the geochemical information to assess the response of the macrobenthic trace maker community to the redox changes at the sediment-water interface. Trace metal proxies indicate a significant, though variable, decreasing oxygenation during sapropel deposition, also supported by important pyritization within sapropel layers.

The recurrent deposition of organic-rich sapropel layers in the eastern Mediterranean Sea (EMS) has been attributed to deep-water stagnation and enhanced biological production. However, the underlying climatic interactions, paleoceanographic processes, and associated ventilation dynamics are still debated. Here, we present a basin-wide reconstruction of circulation systematics during sapropel S1 formation (∼10.8–6.1 kyr BP), using the Nd isotope composition ( e Nd ) as paleo-seawater tracer. Our e Nd data from fish debris and foraminifera tests are remarkably radiogenic compared to today, and spatially and temporally constant. These results predominantly reflect enhanced Nile versus Atlantic contributions, and indicate that EMS deep-water stagnation prevailed below ∼800 m water-depth during S1 formation. Additional e Nd records obtained from bulk sediment leachates show that such stagnation was preconditioned thousand(s) of years prior to S1 initiation by intensified Nile flooding, whereas it terminated with a basin-wide, deep-water renewal. In addition, decoupling of deep waters between the EMS and western Mediterranean Sea (WMS) is evident for the S1-period. Using a box-model for Nd in the EMS, the observed e Nd distribution can be most adequately explained by a 2-fold increase in Nile discharge, and a 50% decrease in the EMS–WMS exchange that was mostly limited to the surface waters alone. The corresponding circulation during S1 was more sluggish and shallow for the EMS, but largely unaffected for the WMS. This implies that deep-water stagnation is a prerequisite for sapropel formation.

We compare geochemical and pollen data of several well-dated, high-resolution cores to provide an integral Holocene overview of Nile outflow, sedimentation, and vegetation in and around the Nile delta. We show that the focus point of the Nile plume varied considerably, as indicated by planktonic foraminifer Globigerinoides ruber oxygen isotopes tracing Nile discharge differences in an east-west delta transect At 13-11.5 cal kyr BP, Nile discharge was low and runoff was predominantly directed to the western part of the delta. Sediment arriving in the delta during that period was dominated by Ethiopian Highland (similar to Blue Nile) material, shown by high Ti/Al values of the bulk sediment, indicating dry conditions in the source area of the Blue Nile. Nile discharge increased from similar to 11.5 cal kyr BP, and was high across the whole delta from similar to 10-6.5 cal kyr BP. During this time, the Ti/Al values decreased within most Nile-delta sediments, suggesting that the relative contribution of Blue-Nile sediment decreased. This was likely due to an increased vegetation cover causing diminished erosion in the Ethiopian Highlands. Nile discharge gradually decreased from similar to 6.5 cal kyr BP to present. This decrease was more abrupt in the Western Province of the delta and became more gradual towards the east as the shrinking Nile runoff was directed there. The gradual decrease in precipitation in the Nile catchment area seems not to be matched by a gradual response in vegetation growing around the river plain in the lower Nile catchment. Our findings suggest a nonlinear response of northeast African vegetation to precipitation from the middle to late Holocene. (C) 2015 Elsevier Ltd. All rights reserved.

Large river systems accumulate, process, and transport huge quantities of organic matter (OM) from their catchments, part of which is exported to the ocean. Although this suite of processes comprises an important component of the global carbon cycle, integrated studies examining the nature and extent of OM processing on a basin-wide scale remain rare. Here, we provide an overview of provenance and composition of OM in suspended and deposited sediments within the Pearl River watershed in South China. We present new data on the organic carbon (OC) and total nitrogen (TN) contents, stable carbon and radiocarbon isotopic compositions of OC (δ 13 C and F m ), as well as grain size distribution and mineral-specific surface area of Pearl River sediments. These results are combined with published data on suspended particulate matter (SPM) and soil profiles in the Pearl River watershed in order to determine the provenance and transformation of OM in this large subtropical fluvial system. We find that the low 14 C contents, expressed as fraction modern (F m ) values, in suspended (F m : 0.58–0.87) and sedimentary OM (F m : 0.38–0.82) are attributed to contributions from 14 C-depleted soils, bedrock, as well as riverine primary productivity (R pp ) that utilizes 14 C-depleted sources of dissolved inorganic carbon (DIC). For SPM, soil OM (F m : 0.87±0.13) is inferred to be the dominant fraction during the wet season, whereas the contributions of R pp (F m : 0.86±0.04) and petrogenic OC (devoid of 14 C) are enhanced during the dry season. This manifests itself in differences in OC soil , OC Rpp , and OC petro contributions in SPM between wet and dry seasons (1.05±0.18 vs. 1.20±0.50%, 0.16±0.03 vs. 0.32±0.15% and 0.21±0.07 vs. 0.38±0.19%). During erosion and transport, the most labile OM in the top soil is rapidly degraded, as indicated by a stronger contribution from soil CO 2 into riverine DIC during the wet season and flood event (39±1% and 45±3%) compared to the dry season (31±2%). River sediments are primarily accumulated during the wet season when suspended sediment fluxes are high. Refractory deep soil OM (F m : 0.74±0.07) dominate in these sediments, whereas moderately labile soil OM components are further degraded during settling and storage. This sedimentary OM is predominantly composed of aged soil (92±4%), with a minor contribution from bedrock (7±4%) and negligible input from R pp (0.2±0%). The longitudinal changes in the composition of suspended and sedimentary OM are mainly controlled by input of R pp and ongoing degradation processes in the river system. The riverine particulate OC flux to the Pearl River estuary and ocean thus contains a mixture of soil, petrogenic and R pp OM, all exhibiting relatively low F m values. The riverine OM transformation and dynamics are important for the short-term carbon cycle, whereas the remaining signature and fate of the extensively processed, refractory OM has implications for the long-term carbon cycle.

Multi-proxy studies are necessary to understand sediment composition and related provenance on continental shelfs. Here it is shown that the spatial distribution of geochemical composition and grain size for surface sediments along the southeastern Italian coast is related to provenance and mechanisms influencing sediment pathways. A northern Adriatic/Italian provenance can be distinguished from a southern Apennine river source. This is done independent of grain size using the element ratios Ce/Ni and Zr/Cr. Furthermore, the origin of organic matter is determined using bulk carbon isotopes and the C/N ratio. Integrating these results with those from complementary studies on δ18O and δ13C of Globigerinoides ruber (white), the BIT index, stable isotopes of plant waxes and dinoflagellate cyst distribution from the same set of samples reveals that: • Sediments from the northwestern Adriatic are transported as far southward as the Gallipoli shelf (eastern Gulf of Taranto) by the Western Adriatic Current (WAC) • Along the WAC, there is a consistent southward decrease in Po river/northern Apennines provenance and a concomitant decrease in terrestrial (soil) organic matter (OM), whereas the percentage of marine OM increases. • The provenance for Gallipoli shelf sediments is for \~80% attributed to Po River/northern Apennines sources and for \~20% to southern Italian sources. • OM in the eastern Gulf of Taranto contains more marine OM than other areas within the WAC, whereas OM and sediments from the western part of the Gulf of Taranto have a more local, riverine provenanc

We present a multiproxy reconstruction of sea surface temperatures (SST) and coastal environmental changes covering the last 600 years on sediments from the Gulf of Taranto, central Mediterranean Sea. The reconstruction is based on UK'37 (alkenones from haptophytes), TEXH86 (membrane lipids of marine crenarchaeota), and d18O and d13C of Globigerinoides ruber (white and pink) and of Uvigerina mediterranea. The amplitudes of the temperature signals reconstructed from I´18O of G. ruber (white), TEXH86 and UK'37 exceed the amplitudes observed in other reconstructions of local and Northern Hemisphere temperature. UKâ�²37-based SSTs reflect mainly winter/spring conditions with an additional influence of changing nutrient supplies related to water column mixing and runoff. TEXH86-based temperatures reflect SSTs of the oligotrophic summer season, while influences from near-coastal areas may complicate its interpretation. Co-variation between both lipid-based SST records suggests a common environmental mechanism during the last 600 years. I´18O of G. ruber (white) also reflects summer conditions and is amplified by changes in salinity and nutrient availability, which are caused by variations in the relative influence of the Western Adriatic Current (WAC) and of the Ionian Surface Waters (ISW). The combination of SST TEX H 86 and I´18O of G. ruber (white) shows that the circulation in the Gulf of Taranto underwent significant changes during the last 600 years.

International audience; Marine sediments at ocean margins vent substantial amounts of methane. Microbial oxidation of the methane released can trigger the precipitation of carbonate within sediments and support a broad diversity of seafloor ecosystems. The factors controlling microbial activity and carbonate precipitation associated with the seepage of submarine fluid over geological time remain poorly constrained. Here, we characterize the petrology and geochemistry of rocks sampled from metre-size build-ups of methane-derived carbonate chimneys located at the Amon mud volcano on the Nile deep-sea fan. We find that these carbonates comprise porous structures composed of aggregated spherules of aragonite, and closely resemble microbial carbonate reefs forming at present in the anoxic bottom waters of the Black Sea. Using U-series dating, we show that the Amon carbonate build-ups formed between 12 and 7 thousand years ago, contemporaneous with the deposition of organic-rich sediments in the eastern Mediterranean, the so-called sapropel layer S1. We propose that the onset of deep-water suboxic or anoxic conditions associated with sapropel formation resulted in the development of intense anaerobic microbial activity at the sea floor, and thus the formation of carbonate chimneys.

X-ray fluorescence (XRF) core-scanning is a convenient non-destructive tool to rapidly assess elemental variations in unprocessed sediments. However, substantial analytical deviations may occur in such data due to physical sedimentary properties. The consequences of these artifacts on element intensities are important for paleoclimatic studies, but as yet have not been adequately studied for high resolution (≤ 1-cm interval) records. We have done a high resolution comparison between results from XRF scanning and from two more conventional methods: XRF with beads and inductively coupled plasma optical emission spectrometry (ICP-OES), both on discrete samples. Our XRF scan data concord reasonably well with those from the conventional methods for most elements. In several discrete intervals large deviations occur that could have been attributed to major paleoceanographic events. However, these deviations appear to be mainly related to water content and distribution. We show that the variability in the water film thickness underneath the plastic foil is highly variable, causing significant apparent variability in all elements from Al to Fe. The unverified use of these elements in ratios can thus lead to deviations in the paleoenvironmental interpretation. Erroneous element (ratio) variability can, however, be recognized and corrected using conventional analytical data of a few discrete samples. The antipathetic behavior of Ca to K or Ti, and their similar behavior to water absorption, leaves their ratios relatively unaffected at variable water film thicknesses. Hence, Ca/K and Ca/Ti ratios are recommended for a preliminary down-core overview of sedimentary variability and for stratigraphic correlations between unprocessed marine cores.

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.

Selective degradation of organic matter in sediments is important for reconstructing past environments and understanding the carbon cycle. Here, we report on compositional changes between and within lipid classes and kerogen types (represented by palynomorph groups) in relation to the organic matter flux to the sea floor and oxidation state of the sediments since the early Holocene for central Eastern Mediterranean site ABC26. This includes the initially oxic but nowadays anoxic presapropelic interval, the still unoxidised lower part of the organic rich S1 sapropel, its postdepositionally oxidised and nowadays organic-poor upper part as well as the overlying postsapropelic sediments which have always been oxic. A general ~ 2.3 times increase in terrestrial and marine input during sapropel formation is estimated on the basis of the total organic carbon (TOC), pollen, spore, dinoflagellate cyst, n -alkane, n -alkanol and n -alkanoic acid concentration changes in the unoxidised part of the sapropel. The long-chain alkenones, 1,15 diols and keto-ols, loliolides and sterols indicate that some plankton groups, notably dinoflagellates, may have increased much more. Apart from the terrestrial and surface water contributions to the sedimentary organic matter, anomalous distributions and preservation of some C 23 –C 27 alkanes, alkanols and alkanoic acids have been observed, which are interpreted as a contribution by organisms living in situ. Comparison of the unoxidised S1 sapropel with the overlying oxidised sapropel and the organic matter concentration profiles in the oxidised postsapropelic sediments demonstrates strong and highly selective aerobic degradation of lipids and palynomorphs. There seems to be a fundamental difference in degradation kinetics between lipids and pollen which may be possibly related with the absence of sorptive preservation as a protective mechanism for palynomorph degradation. The n -alkanes, Impagidinium , and Nematosphaeropsis are clearly more resistant than TOC. The n -alkanols and n -carboxylic acids are about equally resistant whereas the pollen, all other dinoflagellate cysts and other lipids appear to degrade considerably faster, which questions the practice of normalising to TOC without taking diagenesis into account. Selective degradation also modifies the relative distributions within lipid classes, whereby the longer-chain alkanes, alcohols and fatty acids disappear faster than their shorter-chain equivalents. Accordingly, interpretation of lipid and palynomorph assemblages in terms of pre- or syndepositional environmental change should be done carefully when proper knowledge of the postdepositional preservation history is absent. Two lipid-based preservation proxies are tested the diol-keto-ol oxidation index based on the 1,15C 30 diol and keto-ols (DOXI) and the alcohol preservation index (API) whereby the former seems to be the most promising.

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.

The Messinian Salinity Crisis is a dramatic event that took place between 5.96 and 5.33 Ma, and resulted not only in the desiccation and reflooding of the Mediterranean but also in the deposition of 0.3–3 km thick evaporites at its seafloor. There has been considerable controversy on the modes of their formation. The first-stage gypsum deposits are considered to have only formed at silled marginal basins, whereas anoxic marls and dolostones are found at deeper settings. We agree with these observations but reject the coincidental presence of similar sills as being too fortuitous to explain gypsum formation in silled basins alone. Alternatively, we present a unifying mechanism in which gypsum precipitation takes place basin-wide at all shallow-water depths but its preservation is limited to silled marginal basins. Taking a realistic early Messinian scenario, including a moderate primary production rate, the sulphate-consumption rate in the deep water appears to exceed the sulphate supply rate as deduced from reported shallow-water gypsum deposition rates. The consequent lower dissolved sulphate content limits gypsum preservation but permits dolomite formation to take place in the deep water. The often observed concurring anoxic environment and absence of gypsum formation is thus related to diminished dissolved sulphate content via organic matter degradation and not to oxygen-free conditions as such.

In this study we investigate benthic phosphorus cycling in recent continental margin sediments at three sites off the Namibian coastal upwelling area. Examination of the sediments reveals that organic and biogenic phosphorus are the major P-containing phases preserved. High Corg/Porg ratios just at the sediment surface suggest that the preferential regeneration of phosphorus relative to that of organic carbon has either already occurred on the suspension load or that the organic matter deposited at these sites is already rather refractory. Release of phosphate in the course of benthic microbial organic matter degradation cannot be identified as the dominating process within the observed internal benthic phosphorus cycle. Dissolved phosphate and iron in the pore water are closely coupled, showing high concentrations below the oxygenated surface layer of the sediments and low concentrations at the sediment–water interface. The abundant presence of Fe(III)-bound phosphorus in the sediments document the co-precipitation of both constituents as P-containing iron (oxyhydr)oxides. However, highly dissolved phosphate concentrations in pore waters cannot be explained, neither by simple mass balance calculations nor by the application of an established computer model. Under the assumption of steady state conditions, phosphate release rates are too high as to be balanced with a solid phase reservoir. This discrepancy points to an apparent lack of solid phase phosphorus at sediment depth were suboxic conditions prevail. We assume that the known, active, fast and episodic particle mixing by burrowing macrobenthic organisms could repeatedly provide the microbially catalyzed processes of iron reduction with authigenic iron (oxyhydro)oxides from the oxic surface sediments. Accordingly, a multiple internal cycling of phosphate and iron would result before both elements are buried below the iron reduction zone.

One of the primary prerequisites for the application of organic proxies is that they should not be substantially affected by diagenesis. However, studies have shown that oxic degradation of biomarker lipids can affect their relative distribution. We tested the diagenetic stability of the U 37 K ′ and TEX86 palaeothermometers upon long term oxygen exposure. For this purpose, we studied the distributions of alkenones and glycerol dialkyl glycerol tetraethers (GDGTs) in different sections of turbidites at the Madeira Abyssal Plain (MAP) that experienced different degrees of oxygen exposure. Sediments were deposited anoxically on the shelf and then transported by turbidity currents to the MAP, which has oxic bottom water. This resulted in partial degradation of the turbidite organic matter as a result of long term exposure to oxic bottom water. Concentrations of GDGTs and alkenones were reduced by one to two orders of magnitude in the oxidized parts of the turbidites compared to the unoxidized parts, indicating substantial degradation. High-resolution analysis of the Pleistocene F-turbidite showed that the U 37 K ′ index of long chain alkenones increased only slightly (0.01, corresponding to U 37 K ′ , while for other Pliocene/Miocene turbidites it either remained unchanged or decreased substantially (up to 0.06, corresponding to ∼6 °C). Previous observations showed that the BIT index, a proxy for the contribution of soil organic matter to total organic carbon, was always substantially higher in the oxidized part in all the turbidites, as a result of preferential degradation of marine-derived GDGTs. This relative increase in soil-derived GDGTs affects TEX86, as the isoprenoid GDGT distribution on the continent can be quite different from that in the marine environment. Our results indicate that the organic proxies are affected by long term oxic degradation to different extents; this should be taken into account when applying these proxies in palaeoceanographic studies of sediments which have been exposed to prolonged oxic degradation.

The present study investigates hydrocarbon oxidation processes at Isis and Amon mud volcanoes (MV’s), in the eastern Nile deep-sea fan. In the water column, molecular and carbon isotopic signatures of light hydrocarbons indicate that gases rapidly dissolve in seawater and are partially oxidized. In the upper sediments, anaerobic oxidation of the light hydrocarbons takes place, as clearly shown by their molecular and isotopic composition. These processes lead to the presence of a distinct Sulfate–Hydrocarbon Interface at 120–145 cm and 20–50 cm below the seafloor, for Isis and Amon MV’s, respectively. In contrast to processes occurring in the water column, a clear preferential oxidation of methane, propane and n-butane over ethane and i-butane is observed in the anoxic sediments. Furthermore, for the first time, fractionation factors have been determined for the anaerobic oxidation of propane and butane, being respectively −4.80‰ and −0.7‰ for δ13C, and −43.3‰ for δ2H of propane.

In ocean margin sediments both marine and terrestrial organic matter (OM) are buried but the factors governing their relative preservation and degradation are not well understood. In this study, we analysed the degree of preservation of marine isoprenoidal and soil-derived branched glycerol dialkyl glycerol tetraethers (GDGTs) upon long-term oxygen exposure in OM-rich turbidites from the Madeira Abyssal Plain by analyzing GDGT concentrations across oxidation fronts. Relative to the anoxic part of the turbidites ca. 7–20% of the soil-derived branched GDGTs were preserved in the oxidized part while only 0.2–3% of the marine isoprenoid GDGT crenarchaeol was preserved. Due to these different preservation factors the Branched Isoprenoid Tetraether (BIT) index, a ratio between crenarchaeol and the major branched GDGTs that is used as a tracer for soil-derived organic matter, substantially increases from 0.02 to 0.4. Split Flow Thin Cell (SPLITT) separation of turbidite sediments showed that the enhanced preservation of soil-derived carbon was a general phenomenon across the fine particle size ranges (

Although studies have shown that organic-walled dinoflagellate cysts (dinocysts) can undergo species-selective aerobic degradation, the alteration rate of this process is not known. Here we provide data on the decay rates of dinocyst from a degradation experiment in which sediment samples of Holocene age from (a) anoxic Namibian shelf and (b) anoxic part of the eastern Mediterranean S1 sapropel have been exposed to oxic and anoxic conditions in natural environments. The two types of sediment were stored in bags composed of a dialyse membrane that allows oxygen penetration but prevents bacterial exchange. Sediment bags were placed in open containers connected to sediment traps and moored for 15 months in anoxic brines and oxic intermediate waters of the Urania and Bannock Basins areas. Within the short experimental time (15 months), exposure to oxygenated waters resulted in a 24% to 57% reduction in concentration of cysts attributable to Brigantedinium spp. and Echinidinium granulatum. Other taxa such as Spiniferites spp., Lingulodinium machaerophorum and Echinidinium spp. appear to be less sensitive. A slight increase in cyst concentration is observed for Nematosphaeropsis labyrinthus, Echinidinium aculeatum, Operculodinium israelianum, and Impagidinium aculeatum, indicating that these cyst species are more resistant to aerobic degradation. Exposure to anoxic conditions has not lead to detectable differences between initial and exposed composition and concentration. Our study is the first to document that species-selective degradation of dinocysts in oxygenated natural environments is a rapid process that changes considerably dinocyst concentrations and assemblages.

For the high-resolution study of trace metal profiles in laminated anoxic sediments, a specially adapted method of resin embedding has been developed. Fluid displacement is the preferred means of sediment dehydration, offering optimum structural preservation and facilitating desalination. Exchanges of deionized water, acetone, and low-viscosity resin are performed in an oxygen-deficient atmosphere to maintain anoxia in the sediments. Analysis of the rinsing fluids indicates both efficient removal of brine salts and minimal dissolution of redox-sensitive trace metals. This contrasts with oxic fluid displacement experiments, in which several metals appear to be removed from the solid phase during desalination. Laser Ablation-Inductively Coupled Plasma- Mass Spectrometry (LA-ICP-MS) scanning of the embedded blocks shows that the adapted preparation viably preserves both the redox-sensitive chemistry and physical structure of the sediment.

The Isis mud volcano is an active camembert-like mud expulsion structure in the eastern Nile deep-sea fan area. It has been investigated during the NAUTINIL (2003) and MIMES (2004) cruises carried out within the MEDIFLUX project. Active, gas-rich fluid venting occurs at the Isis mud volcano as indicated by enhanced gas content in the sediments, having a measured 7.5 mmol of methane per liter of wet sediment in the central area of the mud volcano. In addition, gas bubble expulsions have resulted in the formation of multiple hydrocarbon plumes in the water column, with methane concentrations as high as 1550 nmol/L, compared to ∼ 1 nmol/L for background levels in deep water. In view of the stable carbon and hydrogen isotopic composition of methane (δ13C = − 55.1‰ VPDB, δD = − 203‰ VSMOW) and of higher hydrocarbons (δ13C of − 30.3‰, − 26.1‰, − 28.4‰, and − 25.0‰ VPDB, for ethane, propane, i-butane and n-butane, respectively), their origin is mainly thermogenic. These isotopic data also show that the wet compounds are co-generated with oil and we suggest they predominantly originate from type II kerogen source rocks of potentially variable maturity levels. At the centre of the mud volcano, the distinct kink observed in the pore water isotopic and dissolved species composition and its depth level change between subsequent cruises indicates a high frequency of fluid/gas expulsion. The seawater signature of the pore fluid in the upper part of the sediment column suggests that each expulsion is followed by a downward migration of overlying seawater. Such downward advection of bottom seawater may not only be related to the replacement of the ejected gas but also to the replacement of lower density pore fluid by bottom seawater. This mechanism is thought to be a common feature at mud volcanoes and gas seepage sites. In the peripheral zone, pore fluid is at seawater concentration and isotopic composition, down to a coring depth of 430 cmbsf. We suggest that the deeper downward advection of bottom seawater is related to the less frequent fluid/gas expulsion occurring at these sites compared to the centre sites. In this paper we show that a combination of geochemical tools used for hydrocarbons and pore water geochemistry is a powerful approach to detect sources of ascending fluid and to reveal post-eruptional fluidodynamic processes within mud volcanoes.

Suboxic sapropel S1 sediments of the eastern Mediterranean carry an untypically light δ98/95Mo 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.

CaCO3 contents in eastern Mediterranean sapropels are generally lower than in the enclosing marl sediments. In sediments of a transect from ∼ 650 to 2100 m water depth at the Sirte continental slope, the opposite feature was observed. Although the increased Sr/Ca ratios observed in these sediments agree with such feature observed in other eastern Mediterranean S1 sediments, their absolute magnitude is much higher. The enhanced Sr/Ca ratio in these sediments is associated with their aragonite content, which for the Sirte transect reaches levels of up to ∼ 40 wt.%. The aragonite content and Sr/Ca ratios in the S1 sediments of this transect decrease with increasing water depth and decrease with distance to the African coast for all eastern Mediterranean cores. In view of the lack of a coherent relationship with sedimentary reduced sulphur contents and porosity, and considering the major amount of aragonite found specifically in the sediments of the Sirte transect, authigenic precipitation can contribute only a limited fraction at most. SEM observation and electron-microprobe analyses showed that the needles and needle clusters are morphologically aragonite, contain the highest Sr/Ca ratio, and are similar to skeleton fragments of the green alga Halimeda. Consequently, a detrital/biogenic source is the likely mechanism for the major part of the aragonite enrichments found in S1 sediments. Possibly, offshore-directed surface water flows related to wind stress and/or enhanced run-off (consistent with enhanced precipitation during sapropel S1) may have assisted in the transport of near-coastal aragonitic organisms to more coast-remote areas.

Fe cycling at two sites in the Mediterranean Sea (southwest of Rhodes and in the North Aegean) has been studied, combining the pore water determination of nutrients, manganese, and iron, citrate-bicarbonate-dithionite (CDB) and total sediment extractions, X-ray diffraction, and 57Fe Mossbauer spectroscopy (MBS). At the Rhodes site, double peaks in the CDB-extractable Mn and Fe profiles indicate non-steady-state diagenesis. The crystalline iron oxide hematite, identified at both sites by room temperature (RT) MBS, appears to contribute little to the overall Fe reduction. MBS at liquid helium temperature (LHT) revealed that the reactive sedimentary Fe oxide phase was nanophase goethite, not ferrihydrite as is usually assumed. The pore water data at both sites indicates that upon reductive dissolution of nanophase goethite, the upward diffusing dissolved Fe2+ is oxidized by Mn oxides, rather than by nitrate or oxygen. The observed oxidation of Fe2+ by Mn oxides may be more common than previously thought but not obvious in sediments where the nitrate penetration depth coincides with the Mn oxide peak. At the Rhodes site, the solid-phase Fe(II) increase occurred at a shallower depth than the accumulation of dissolved Fe2+ in the pore water. The deeper relict Mn oxide peak acts as an oxidation barrier for the upward diffusing dissolved Fe2+, thereby keeping the pore water Fe2+ at depth. At the North Aegean site, the solid-phase Fe(II) increase occurs at approximately the same depth as the increase in dissolved Fe2+ in the pore water. Overall, the use of RT and cryogenic MBS provided insight into the solid-phase Fe(II) gradient and allowed identification of the sedimentary Fe oxides: hematite, maghemite, and nanophase goethite.

In studying the Holocene–late Pleistocene record of the Eastern Mediterranean, considerable Emiliania huxleyi size/shape variation not clearly assignable to primary or secondary calcification was observed. Accordingly, different morphotypes were distinguished by light microscope (LM). A subsequent scanning electron microscope (SEM) analysis of selected samples has indicated that Emiliania huxleyi coccoliths are variably affected by carbonate diagenesis in these sediments. A series of diagenetic stages were qualitatively defined, comprising well-preserved specimens, three overgrowth (OG1 to OG3) and one etching (E1) stage. Comparing SEM and LM observations, a tentative correlation between the E. huxleyi calcified LM-morphotypes and E. huxleyi SEM-overgrowth stages is proposed here. Our study not only indicates that Emiliania huxleyi coccoliths are strongly influenced by carbonate diagenesis, but also that they show effects of carbonate precipitation and dissolution much more clearly than other coccoliths. The relative abundances of the different LM-morphotypes were used to define an E. huxleyi overgrowth index (EXO) that qualitatively estimates carbonate precipitation/dissolution on coccoliths in this sediment. This resulted in definition of five ‘‘Diagenetic’’ intervals (D1 to D5). Deposition of sapropel S1 was a time of good preservation with variable dissolution and no overgrowth of E. huxleyi coccoliths, whereas calcite overgrowth was high during the Last Glacial Maximum (LGM) and interglacial period and, to a lesser extent, during the Younger Dryas and through the last 5 ka. D 2004 Elsevier B.V. All rights reserved.

A high-resolution study of an active Fe 2+ /Fe 3+ redox horizon has been carried out on sediments of the central equatorial Atlantic. The multidisciplinary approach combining geochemical and rock-magnetic parameters gives evidence of the interrelation of the redox horizon with the last change from glacial to interglacial conditions (T1). Distinct enrichments of redox-sensitive elements (Mn, Fe, V, and U) reveal a characteristic depth-sequence, indicating non-steady-state diagenetic conditions caused by a decrease in productivity and an increase in oxygen content in the bottom water during T1 and a reversal during the Holocene. Thus, the redox boundaries first moved down into the sediment and subsequently upwards. The movement of the redox boundaries led to the development of conspicuous double peaks for Fe and Mn. The reconstruction based on geochemical data is supported by susceptibility and magnetization measurements of the sediments displaying well-defined anomalies in the vicinity of active and paleo redox boundaries. The combination of geochemical and rock-magnetic parameters, like the ferrimagnetic susceptibility, and total Fe concentration ( χ f /Fe) are suitable for characterizing distinct zones of dissolution and precipitation of ferromagnetic mineral phases (e.g. magnetite). Moreover, the small scale movement of the Fe 2+ /Fe 3+ redox-boundary, could be traced in detail by overlaying the peak-shape pattern of V/Al and of χ f / χ tot .

The carbon (C) and phosphorus (P) geochemistry of sapropels from four sites in the eastern Mediterranean Sea was determined to obtain more insight into the role of differences in sediment accumulation rates and bottom water anoxia on P regeneration and burial in sediments. Sediment Corg/Porg (with ORG=organic) ratios above Redfield indicate enhanced regeneration of P relative to C from organic matter during formation of the most recent sapropel S1 and a Pliocene sapropel (ODP-site 969E; i-282c). Release of P from Fe-oxides was relatively unimportant. Increased burial of Ca-P (authigenic carbonate fluorapatite and/or biogenic hydroxyapatite) occurred but was of minor importance compared to the enhanced P release from organic matter. For sapropel S1, Corg/Porg and Corg/Preac, (with REAC=reactive, defined as the sum of organic, Fe-bound, authigenic and biogenic Ca-P) ratios decreased with increasing sedimentation rate and oxygen exposure and decreasing water depth. Whether the water column in the deep basin was dysoxic/semi-euxinic (S1) or euxinic (Pliocene) does not appear to affect the estimated burial efficiencies of Porg and Preac. Enhanced Corg burial under the euxinic water column explains the much higher Corg/Porg and Corg/Preac ratios in the Pliocene sapropel (on average ~2860 and ~760, respectively) compared to sapropel S1 (on average ~530 and ~160, respectively)

Despite growing concerns about potential enhancement of global warming and slope failure by methane produced by gas hydrate dissociation, much uncertainty surrounds estimates of gas hydrate reservoir sizes, as well as methane fluxes and oxidation rates at the sea floor. For cold seep sediments of the eastern Mediterranean Sea, depth-dependent methane concentrations and rates of anaerobic oxidation of methane (AOM) are constrained by modeling the measured pore-water sulfate profile. The calculated dissolved methane distribution and flux are sensitive to the advective flow velocity, which is estimated from the depth distributions of conservative pore-water constituents (Na, B). Near-complete anaerobic oxidation of the upward methane flux of ∼6.0 mol m−2 yr−1 is supported by the depth distributions of indicative biomarkers, and the carbon isotopic compositions of organic matter and dissolved inorganic carbon. Pore-water and solid-phase data are consistent with a narrow depth interval of AOM, 14–18 cm below the sediment–water interface. Based on an isotopic mass balance, the biomass of the microbial population carrying out oxidation of methane coupled to sulfate reduction at the given methane flux represents ∼20% of the total organic carbon, which is a significant pool of in situ formed organic matter. Model results indicate that the asymptotic methane concentration is reached a few meters below the sediment surface. The predicted asymptotic concentration is close to the in situ saturation value with respect to gas hydrate, suggesting that the rate of shallow gas hydrate formation is controlled by the ascending methane flux. The proposed model approach can be used to predict the formation of gas hydrate, and to quantify methane fluxes plus transformation rates in surface sediments where fluid advection is an important transport mechanism.

A detailed sequential extraction scheme (MESEX) was developed to distinguish Fe and Mn phases in eastern Mediterranean sediments. After calibration and validation using single natural minerals and a mixed mineral standard, MESEX was applied to Holocene eastern Mediterranean sediments from (1) a former brine basin, and (2) a normal setting, including the organic-rich sapropel S1. In both sediments the Mn(II)/Mn(III,IV) redox boundary is clearly distinguished with carbonate-related Mn being enriched below, and Mn oxides occurring only above it. A clear Fe(II)/Fe(III) redox boundary is present in the normal eastern Mediterranean sediments and is located just below the Mn(II)/Mn(III,IV) redox boundary. The Fe(II)/Fe(III) boundary closely coincides with the visible boundary between the lower unoxidised and the upper oxidised (burned-down) part of the original sapropel S1 interval. Pyrite is only present within the unoxidised interval, whereas Fe oxides are abundant above it. The Fe(II)/Fe(III) redox boundary in the former brine sediments resides on top of the organic-enriched sediments, as deduced from the distribution of Fe oxides and pyrite. As a result of burn-down of the sapropel S1 unit in the normal sediments, a vanadium peak has been formed below the oxidation front, whereas no such V peak was observed in the former brine sediments. This, together with the location of the Mn(II)/Mn(III,IV) redox boundary well above the organic-enriched sediments, suggests that no burn-down has taken place into the sapropelic sediments of the former brine basin, resulting in the preservation of the relationships of trace metal to organic carbon or pyrite. In these latter sediments, Mn and Co appear to be associated with pyrite, whereas Ni, Cu and Zn, as well as V, are more related to organic matter. On the basis of MESEX, variations have also been detected in the terrigenous component, i.e. aluminosilicates. (Fe/Al)clay, (Mg/Al)clay, and several trace metal to Al ratios are higher in sapropelic than in non-sapropelic sediments. These results indicate that sources of terrestrial material have been different during sapropel times compared to the period immediately after it. On the other hand, the fairly constant K/Alclay ratio suggests that no major changes may have occurred in the relative illite contribution.

A sequential extraction method (BASEX) was developed to determine the different Ba fractions in sediments. Calibration of BASEX with pure barite and a home-made mixed mineral standard showed that barite is separated from all other major Ba containing mineral phases, such as clay minerals and Fe and Mn oxides. This method permits the direct determination of sedimentary barite content and of the Ba/Al ratio of clay, and is, therefore, a useful tool in palaeoclimatic studies. Application of BASEX to eastern Mediterranean sediments, including sapropel S1, revealed that the enrichment in Ba concentrations observed in this sapropel consists predominantly of barite. The relationship of barite-Ba with organic carbon in sapropel S1 sediments appears to be independent of water depth, of organic matter fluxes and of the sedimentation rate for cores ranging from 2150 to 3300 m water depth. Apparently, organic carbon remineralisation has been virtually absent in the water column deeper than 2150 m. This might have been caused by suboxic to anoxic conditions present in the deep eastern Mediterranean basin during the formation of sapropel S1. Because of the constant relationship between barite and organic carbon in sapropelic sediments, we suggest that the barite content can be used to quantify the initial organic carbon content of the sediment in the oxidised sapropel interval.

Studies of past glacial cycles yield critical information about climate and sea-level (ice-volume) variability, including the sensitivity of climate to radiative change, and impacts of crustal rebound on sea-level reconstructions for past interglacials. Here we identify significant differences between the last and penultimate glacial maxima (LGM and PGM) in terms of global volume and distribution of land ice, despite similar temperatures and radiative forcing. Our analysis challenges conventional views of relationships between global ice volume, sea level, seawater oxygen isotope values, and deep-sea temperature, and supports the potential presence of large floating Arctic ice shelves during the PGM. The existence of different glacial ‘modes’ calls for focussed research on the complex processes behind ice-age development. We present a glacioisostatic assessment to demonstrate how a different PGM ice-sheet configuration might affect sea-level estimates for the last interglacial. Results suggest that this may alter existing last interglacial sea-level estimates, which often use an LGM-like ice configuration, by several metres (likely upward).

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.

Sediments from a boxcore in the previously anoxic brine-filled Poseidon Basin, eastern Mediterranean, have been studied and compared to sediments deposited in a ‘normal’ eastern Mediterranean environment. The boxcore can be divided into three main sedimentary intervals based on AMS-radiocarbon ages, foraminiferal and geochemical zonations. From the base of the core upwards these are: (1) 12.3‐31.2 cm, organic-rich sediments redeposited from within the brine; (2) 6.6‐12.3 cm, sediment containing a ‘cold’ foraminifera fauna redeposited from above the brine into the basin while the brine was still present; (3) 0‐6.6 cm, oxic pelagic sediment accumulated since the reoxygenation of Poseidon Basin which occurred1800 yrs BP. Near the base of the latter unit, a Mn-oxide peak has formed and it marks the present boundary between oxic and suboxic environments. A progressive downward oxidation front, which is usually found in ‘normal’ sapropel S1 sediments, has never formed in Poseidon Basin sediments. This has resulted in the preservation of the relationship between organic carbon and organic-related trace elements, e.g. Se, in the organic-rich sediments of Poseidon Basin, whereas such a relationship has been obliterated in ‘normal’ sapropel S1 sediments. On the basis of the carbonate content as well as the Sr=Ca ratio, preservation of carbonates appears to be better in the brine sapropel sediments of BC15 than it is in ‘normal’ sapropel S1 sediments. The high opal content of BC15 shows that biogenic opal is also much better preserved. The overall lower Corg=Ba ratio in BC15 suggests a better preservation of barite relative to that of organic carbon in shallow brine sediments, but is as yet inconclusive for the organic carbon preservation potential of brine relative to ‘normal’ unoxidised sediments. © 1999 Elsevier Science B.V. All rights reserved.

Sulphur isotope compositions and S/C ratios of organic matter were analysed in detail by combustion-isotope ratio monitoring mass spectrometry (C-irmMS) in eastern Mediterranean sediments containing three sapropels of different ages and with different organic carbon contents (sapropel S1 in core UM26, formed from 5–9 ka ago with a maximum organic carbon content of 2.3 wt%; sapropel 967 from ODP Site 160-967C, with an age of 1.8 Ma and a maximum organic carbon content of 7.4 wt%; and sapropel 969 from ODP Site 160-969E, with an age of 2.9 Ma and a maximum organic carbon content of 23.5 wt%). Sulphur isotopic compositions (δ34S) of the organic matter ranged from -29.5 to +15.8‰ and the atomic S/C ratio was 0.005 to 0.038. The organic sulphur in the sediments is a mixture of sulphur derived from (1) incorporation of 34S-depleted inorganic reduced sulphur produced by dissimilatory microbial sulphate reduction; and (2) biosynthetic sulphur with an isotopic signature close to seawater sulphate. The calculated biosynthetic fraction of organic sulphur in non-sapropelic sediments ranges from 68–87%. The biosynthetic fraction of the organic sulphur of the sapropels (60–22%) decreases with increasing organic carbon content of the sapropels. We propose that uptake of reduced sulphur into organic matter predominantly took place within sapropels where pyrite formation was iron-limited and thus an excess of dissolved sulphide was present for certain periods of time. Simultaneously, sulphide escaped into the bottom water and into sediments below the sapropels where pyrite formation occurred.

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, χ 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.

The origin of hypersaline brines from Urania and Bannock deep anoxic basins in the eastern Mediterranean Sea has been investigated by integrating geochemical data and boron isotopic ratios. Bottom brines from Urania basin have chloride contents up to 4200 mmole/kg H2O and a marine Na/Cl ratio (0.87). All the other ionic ratios are different from the marine ratios and show a relative enrichment in Ca, K, Br, and B and depletion in Mg and SO4, as normalized to the chloride ion. The δ11B values of the Urania brines (δ11B = 29.8 ± 2.9‰; n = 7) are lower than that of Mediterranean seawater (39‰). The concentrations of Cl and Na, which make up 95% of the total dissolved ions (in molal units), suggest that the Urania brines were derived from eightfold evaporated seawater. The relative enrichment of Ca and depletion of Mg and SO4 reflect dolomitization, gypsum precipitation, and sulfate reduction processes which modified the original evaporated seawater while the brines were entrapped as interstitial waters in the sedimentary section of the Mediterranean. The relative enrichments of Br, B, and K, and the low δ11B value of the Urania brines suggest high-temperatures interactions of the evaporated sea water with sediments. Mass-balance calculations suggest that desorption of exchangeable B from the sediments (δ11B ∼ 20‰) modified the marine B isotopic composition of the original eightfold evaporated seawater. Potassium was also leached from clay minerals whereas Br was contributed from degradation of organic matter in the sediments. This is consistent with a thermal anomaly (up to 45°C) recorded at depth in the region of Urania basin. In contrast, bottom brines and shallow interstitial fluids from Bannock basin with low temperatures (15°C) show marine δ11B (δ11B = 39.6 ± 2.8‰; n = 5; 38.5 ± 2.2‰; n = 5, respectively) and B/Cl ratios (7 × 10−4). The B isotope data confirm that the Bannock brines were derived from twelvefold evaporated seawater. We argue that the brines from both basins are relics of fossil evaporated seawater that was entrapped in Late-Miocene sediments and accumulated in the deep basins of the Mediterranean seafloor.

A set of oxidized and unoxidized sediment intervals from the f-turbidite identified in two piston cores from the Madeira Abyssal Plain (MAP) was analyzed for calcium carbonate, total organic carbon (TOC), total nitrogen (TN), stable carbon composition of TOC (δ13C toc ), total hydrolyzable amino acids (THAA), total neutral sugars (TSUG), lignin phenols (LIG), two different lipid biomarkers of marine phytoplankton origin and vascular plantwax n-alkanes and n-acids. Comparison shows changes for all properties depicting the effect of post-depositional, aerobic oxidation. The oxidation process re-mineralized approximately 80% of the TOC and approximately 60% of the TN in the original deposit and left the residual organic matter depleted in 13C by 1.7–2.9‰ THAA and TSUG account for 10% or less of the TOC in all samples leaving approximately 90% of the TOC chemically unidentified. THAA, TSUG, LIG, marine phytoplankton biomarkers and plantwax n-acids were lost from the oxidized deposit to an extent as great as that for TOC. Two non-protein amino acids (β-alanine and γ-aminobutyric acid) and plant wax n-alkanes displayed much less degradation (9–37%) and concentrated 3.3–4.8 times relative to TOC by the oxidation process. These observations show that both marine and terrestrial components contribute to the re-mineralized TOC fraction. A binary mixing approach was used to model quantitatively the change in δ13C toc and plantwax n-alkane concentration. Results suggest that terrestrial organic carbon contributes approximately 15% to the TOC content of the original turbidite, its abundance increases approximately 2–4 times as a consequence of the oxidation process and approximately 40 and 90% of the terrestrial and marine component of TOC in the original turbidite, respectively, was destroyed by the oxidation process. Although selective preservation of terrestrial relative to marine organic carbon is a well-documented phenomenon in sedimentary processes, this study represents the first attempt to assess the sensitivity of terrestrial organic matter to oxidative degradation in a sedimentary environment.

The occurrence of organic-walled dinoflagellate cysts in (fossil) sediments depends on several factors, including as the ecological preferences of the cyst-forming dinoflagellates, cyst production, transport and preservation. Although laboratory experiments have shown that several cyst species are sensitive to chemical treatment, no information about the selective preservation of dinoflagellate cyst species in natural environments has previously been presented. Here, we present data on the effects of oxygen availability in bottom sediments on a cyst assemblage from the ungraded Madeira Abyssal Plain f-turbidite of which only the upper layer has been oxidized. Based on differences in species composition between the oxidized and underlying, unoxidized layers of this turbidite, the influence of oxygen availability on the preservation of individual species has been estimated. Cyst species have been classified in ascending order of resistance to oxygen availability in sediments as: (1) highly sensitive (cysts formed by Protoperidinium species), (2) moderately sensitive (e.g. Spiniferites species), (3) moderately resistant (e.g. Impagidinium paradoxum and Nematosphaeropsis labyrinthus) and (4) resistant (e.g. Impagidinium aculeatum).

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 μmoles 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 δ34S values for both pyritic sulphur (δ34S: −19%c to −39%) and humic sulphur (δ34S: −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.

Quantitative analyses on calcareous nannofossil assemblages on high temporal resolution (600-800 years) have been carried out from Core KC01B in the Ionian Sea (Eastern Mediterranean) throughout Marine Isotope Stage (MIS) 13-9, between 500 and 300 ka. This is an interval of considerable climate changes, known as the Mid-Brunhes event, which includes MIS 11, considered as a possible analogue for future interglacial conditions. In the Mediterranean core, the interval is characterized by the dominance of Gephyrocapsa spp., as also known from ocean records. Calcareous nannofossil abundance fluctuations have been interpreted in terms of modification of sea surface primary productivity/water stratification and temperature. Specifically, the increase in abundance of Gephyrocapsa caribbeanica and small Gephyrocapsa coupled with decreases of Florisphaera profunda, Syracosphaera spp. and Rhabdosphaera spp. suggests enhanced primary productivity/mixed surface waters during interglacial stages and at the Terminations, which can be interpreted in terms of interaction between climate changes and mesoscale oceanographic circulation. On the other hand, distributions of Calciosolenia spp., Oolithotus spp. and Umbilicosphaera sibogae, which are in phase with delta O-18 curve showing higher abundances at the lighter values of the marine isotope record, are considered as warm-water indicators. Biotic proxies point to peculiar climate dynamics through the MIS 12-11 transition (i.e. Termination V). High productive, cool, low salinity and turbid surface waters characterize the early MIS 11(421-408 ka) and likely reflect enhanced continental humidity/monsoon activity over North Africa and increased runoff into the basin. A late surface water warming with respect to Termination V is established at about 403 ka, during a period of low insolation forcing, almost coeval with the deposition of sapropel S11. A climate optimum, lasting about 15 ky (403-389 ka), is then recorded during a period of low insolation forcing centred at 398 ka. The later part of MIS 11 is characterized by climate deterioration at about 389 ka. Comparison with results from subtropical to polar Atlantic records suggests a remarkable relation between Mediterranean and Atlantic climate regimes.

Fossil remnants of benthic foraminifera consist of carbonate tests and their organic linings. The macromolecular and stable isotopic composition of these benthic foraminiferal organic linings was characterized to evaluate their potential use as paleoclimate proxies. Using Curie point pyrolysis–GC–MS (Py–GC–MS) we show that benthic foraminiferal organic linings consist of protein and polysaccharides, bound together in a complex macromolecular structure. Both chitin derivatives and traces of guaiacols and syringols, usually assigned to lignin are found. Although the five species of benthic foraminifera all contain chitin derivatives and proteins, the relative contribution of these compounds tends to vary considerably. Oxygen stable isotopic analyses of the organic linings of the benthic foraminiferal species Ammonia tepida indicates that ∂ 18 O OL values are in line with fractionation between seawater and organic matter. In contrast a ∂ 13 C deliberate tracer experiment showed that metabolic carbon is the main source for the carbon fixed in the organic lining. The different pathways of carbon and oxygen stable isotopes into the foraminiferal linings have important implications for future proxy development as they reflect different components of the environment compared to the carbonate bound stable isotopes. Still, the future application of benthic foraminiferal organic linings and their isotopic values critically relies on improvements in calibration and sample size required for isotopic analyses.

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. N-15 isotope pairing incubation experiments showed the production of N-29(2) and N-30(2) 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 N-2 L-1 day(-1) while denitrification was a major N-2 production pathway, accounting for more than 85.5 % of total N-2 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.

Organic carbon, sulphur, δ13Corg, iron, manganese and calcium have been measured across a subsurface-weathering front in Pliocene sediments in southern Sicily. The results show an almost quantitative removal of Corg and sulphur and an increase in iron and manganese oxides over the weathering front, accompanied with a significant shift of the δ13Corg to lower values. These data are among the first to support the rapid, extensive weathering of sedimentary organic matter and sulphur, a basic assumption made in global biogeochemical models on a Phanerozoic timescale.

High-resolution sedimentary records of major and minor elements (Al, Ba, Ca, Sr, Ti), total organic carbon (TOC), and profiles of pore water constituents (View the MathML sourceSO42-, CH4, Ca2+, Ba2+, Mg2+, alkalinity) were obtained for two gravity cores (core 755, 501 m water depth and core 214, 1686 m water depth) from the northwestern Black Sea. The records were examined in order to gain insight into the cycling of Ba in anoxic marine sediments characterized by a shallow sulfate–methane transition (SMT) as well as the applicability of barite as a primary productivity proxy in such a setting. The Ba records are strongly overprinted by diagenetic barite (BaSO4) precipitation and remobilization; authigenic Ba enrichments were found at both sites at and slightly above the current SMT. Transport reaction modeling was applied to simulate the migration of the SMT during the changing geochemical conditions after the Holocene seawater intrusion into the Black Sea. Based on this, sediment intervals affected by diagenetic Ba redistribution were identified. Results reveal that the intense overprint of Ba and Baxs (Ba excess above detrital average) strongly limits its correlation to primary productivity. These findings have implications for other modern and ancient anoxic basins, such as sections covering the Oceanic Anoxic Events which Ba is frequently used as a primary productivity indicator. Our study also demonstrates the limitations concerning the use of Baxs as a tracer for downward migrations of the SMT: due to high sedimentation rates at the investigated sites, diagenetic barite fronts are buried below the SMT within a relatively short period. Thus, ‘relict’ barite fronts would only be preserved for a few thousands of years, if at all.

phylotypes, which were previously only detected in anoxic Black Sea sediments. In the same section of the core, the most abundant haptophyte sequence showed highest similarity with uncultivated haptophytes that were previously shown to grow mixotrophically as predators of picocyanobacteria, an adaptation that promotes growth in oligotrophic marine waters. Sequences with highest similarities to clones found in marine surface waters predominated in the S1 after ∼8 14 C kyr B.P. We discuss whether the shifts in haptophyte and dinoflagellate populations inferred from the preserved DNA reflect known environmental changes that occurred during the formation of sapropel S1.

A multicomponent diagenetic model was developed and applied to reconstruct the conditions under which the most recent sapropel, S1, was deposited in the eastern Mediterranean Sea. Simulations demonstrate that bottom waters must have been anoxic and sulphidic during the formation of S1 and that organic matter deposition was approximately three times higher than at present. Nevertheless, most present day sediment and pore water profiles — with the exception of pyrite, iron oxyhydroxides, iron-bound phosphorus and phosphate — can be reproduced under a wide range of redox conditions during formation of S1 by varying the depositional flux of organic carbon. As a result, paleoredox indicators (e.g., Corg:S ratio, Corg:Porg ratio, trace metals) are needed when assessing the contribution of oxygen-depletion and enhanced primary production to the formation of organic-rich layers in the geological record. Furthermore, simulations show that the organic carbon concentration in sediments is a direct proxy for export production under anoxic bottom waters. The model is also used to examine the post-depositional alteration of the organic-rich layer focussing on nitrogen, phosphorus, and organic carbon dynamics. After sapropel formation, remineralisation is dominated by aerobic respiration at a rate that is inversely proportional to the time since bottom waters became oxic once again. A sensitivity analysis was undertaken to identify the most pertinent parameters in regulating the oxidation of sapropels, demonstrating that variations in sedimentation rate, depositional flux of organic carbon during sapropel formation, bottom water oxygen concentration, and porosity have the largest impact. Simulations reveal that sedimentary nutrient cycling was markedly different during the formation of S1, as well as after reoxygenation of bottom waters. Accumulation of organic nitrogen in sediments doubled during sapropel deposition, representing a significant nitrogen sink. Following reventilation of deep waters, N2 production by denitrification was almost 12 times greater than present day values. Phosphorus cycling also exhibits a strong redox sensitivity. The benthic efflux of phosphate was up to 3.5 times higher during the formation of S1 than at present due to elevated depositional fluxes of organic matter coupled with enhanced remineralisation of organic phosphorus. Reoxygenation of bottom waters leads to a large phosphate pulse to the water column that declines rapidly with time due to rapid oxidation of organic material. The oxidation of pyrite at the redox front forms iron oxyhydroxides that bind phosphorus and, thus, attenuate the benthic phosphate efflux. These results underscore the contrasting effects of oxygen-depletion on sedimentary nitrogen and phosphorus cycling. The simulations also confirm that the current conceptual paradigm of sapropel formation and oxidation is valid and quantitatively coherent.

[1] High-resolution laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) scanning of laminated sediments from the Urania basin is used to investigate short-time-scale variability in export productivity and redox conditions during the formation of eastern Mediterranean sapropel S1. Sedimentary enrichments of molybdenum (Mo), vanadium (V), and uranium (U) reflect deep-water redox conditions, most likely those near to the seawater-brine interface, while enrichment of Ba is related to biogenic barite and hence to export productivity. The enrichments of all four elements show strong variability on multidecadal to multicentennial time scales throughout S1. A partial decoupling of export productivity from redox conditions at the height of sapropel formation suggests that hydrographic changes, i.e., a variable ventilation rate of the eastern Mediterranean, played an important role in determining deep-water redox conditions. A pronounced switch is observed in the enrichments of redox-sensitive trace metals, from dominantly 300–600 year variability during early S1 to dominantly 100–300 year variability during late S1, indicating a change in the mean frequency of variability in the ventilation rate. The presence of a similar shift in the frequency of tropical and extratropical climate records at this time suggests that ventilation of the eastern Mediterranean was coupled to global climate variability.