A high‐resolution chemical and structural study of framboidal pyrite formed within a low‐temperature bacterial biofilm

A novel, anaerobically grown microbial biofilm, scraped from the inner surface of a borehole, 1474 m below land surface within a South African, Witwatersrand gold mine, contains framboidal pyrite. Water flowing from the borehole had a temperature of 30.9 °C, a pH of 7.4, and an Eh of –50 mV. Examination of the biofilm using X‐ray diffraction, field emission gun scanning electron microscope equipped for energy dispersive X‐ray microanalysis demonstrated that the framboids formed within a matrix of bacteria and biopolymers. Focused ion beam sectioning of framboids followed by NEXAFS measurements using both scanning transmission X‐ray microscopy and X‐ray photoelectron emission microscopy revealed that the pyrite crystals grew within an organic carbon matrix consisting of exopolysaccharides and possibly extracellular DNA, which is intuitively important in sulfide mineral diagenesis. Growth of individual pyrite crystals within the framboid occurred inside organic templates confirms the association between framboidal pyrite and organic materials in low‐temperature diagenetic environments and the important role of microenvironments in biofilms in regulating geochemical cycles.     

Gut content fossilization and evidence for detritus feeding habits in an enrolled trilobite from the Cambrian of China

Enrolment was a major defensive strategy for trilobites that significantly contributed to their evolutionary success. The ability to enrol also helped to constrain the morphological evolution of trilobites, which in part was driven by the need to improve this capability to encapsulate the soft parts of the body within the mineralized dorsal exoskeleton. Here, we describe a unique example of gut content fossilization in an enrolled trilobite from the Cambrian of China, and we propose a taphonomic scenario that considers the possible implication of enrolment in this exceptional preservation. A micro‐facies analysis indicates that the specimen was entombed during an obrution event and remained intact due to limited infaunal activity. The encapsulation of the body did not prevent the decay of soft tissues, but it permitted the delicate gut content to be protected during diagenesis. In isolating the decaying soft tissues from the external environment, enrolment might also have favoured the establishment of microenvironmental conditions conducive to the precipitation of pyrite framboids. Within the gut, the formation of such crystals may have led to the consolidation of the ingested material. These results suggest that fossilized gut contents might be quite common in enrolled trilobites. Textural and compositional analyses reveal that the gut content is similar to the sediment surrounding the fossil except for the presence of pyrite framboids that indicate higher initial organic matter content. The complete enrolment of the body argues against an accidental ingestion of this material or a diagenetic origin for it. Accordingly, detritus feeding habits are inferred for this ptychopariid trilobite.     

Petrography and high-resolution geochemical records of Lower Jurassic manganese-rich deposits from Monte Mangart,Julian Alps

Deposits with unusually high Mn contents sampled at Monte Mangart in the Julian Alps include organic-rich marlstone and black shale with interbedded manganoan and siliceous limestone, which were deposited during the early Toarcian Oceanic Anoxic Event. Mn enrichment during that period has been related to global sea-level change coincident with increasing subsidence rate. The formation of Fe–Mn nodules, marking a hardground at the base of the Monte Mangart section, seems to be triggered by release of Mn from remote hydrothermal vents into a region of relatively elevated submarine topography where oxidizing conditions prevailed. However, very high Mn contents in carbonate phases above the hardground imply an additional diagenetic source of this element in the lower part of this section. The whole stratigraphic sequence (ca 30 m) displays a transition from Mn-rich (up to 8.8%) sediments, in the lower part, to Mn-poor (less than 1.8%) sediments in the middle and upper parts. The drastic decrease in Mn content's up-section is accompanied by a clear decrease in the mean size of pyrite framboids, indicating more intense anoxia/euxinia in the water column. In the presence of Mn²⁺, conditions of high alkalinity induced precipitation of Mn carbonates during early diagenetic processes. Negative δ¹³C_carb values coincident with high Mn contents indicate involvement of organic matter in the mineralization process. The striking similarity of Ce/Ce* and Mn profiles demonstrates that, consistent with redox-chemistry of Mn and Ce under anoxic conditions, Ce³⁺ and Mn²⁺ were mobilized and released into pore water where precipitation of Mn carbonates occurred.     

Microbial silica deposition in geothermal hot waters

A combined use of molecular ecological techniques and geochemical surveys revealed that thermophilic or hyperthermophilic microorganisms living in geothermal environments are likely to be implicated in the formation of biogenic siliceous deposits. Electron microscopic observations indicated that numerous microorganism-like fabrics were preserved in naturally occurring siliceous deposits such as siliceous sinter, geyserite, and silica scale, which suggests microbial contribution to silica precipitation. Molecular phylogenetic analyses suggested that extreme thermophilic bacteria within the genera Thermus and Hydrogenobacter are predominant components among the indigenous microbial community in siliceous deposits formed in pipes and equipment of Japanese geothermal power plants. These bacteria seem to actively contribute to the rapid formation of huge siliceous deposits. Additionally, in vitro examination suggested that Thermus cells induced the precipitation of supersaturated amorphous silica during the exponential growth phase, concomitant with the production of a specific cell envelope protein. Dissolved silica in geothermal hot water may be a significant component in the maintenance of position and survival of microorganisms in limited niches.     

Biogeochemical changes at the sediment–water interface during redox transitions in an acidic reservoir: exchange of protons,acidity and electron donors and acceptors

Redox transitions induced by seasonal changes in water column O₂ concentration can have important effects on solutes exchange across the sediment–water interface in systems polluted with acid mine drainage (AMD), thus influencing natural attenuation and bioremediation processes. The effect of such transitions was studied in a mesocosm experiment with water and sediment cores from an acidic reservoir (El Sancho, SW Spain). Rates of aerobic organic matter mineralization and oxidation of reduced inorganic compounds increased under oxic conditions (OX). Anaerobic process, like Fe(III) and sulfate reduction, also increased due to higher O₂ availability and penetration depth in the sediment, resulting in higher regeneration rates of their corresponding anaerobic e^? acceptors. The contribution of the different processes to oxygen uptake changed considerably over time. pH decreased due to the precipitation of schwertmannite and the release of H⁺ from the sediment, favouring the dissolution of Al-hydroxides and hydroxysulfates at the sediment surface. The increase in dissolved Al was the main contributor to water column acidity during OX. Changes in organic matter degradation rates and co-precipitation and dissolution of dissolved organic carbon and nitrogen with redox-sensitive Fe(III) compounds affected considerably C and N cycling at the sediment–water interface during redox transitions. The release of NO₂^? and NO₃^? during the hypoxic period could be attributed to ammonium oxidation coupled to ferric iron reduction (Feammox). Considering the multiple effects of redox transitions at the sediment–water interface is critical for the successful outcome of natural attenuation and bioremediation of AMD impacted aquatic environments.     

Spicules of hexactinellid sponges (Hexactinellida: Porifera) as natural composite materials

This paper reviews studies on the hexactinellid glass sponges (Hexactinellida: Porifera) that have organic silica spicules. According to its physical properties (microdensity, Young’s modulus, and light transmission), the material of the spicules is similar to amorphous silica; however, sponge spicules are birefringent, which suggests that they have a highly ordered crystal-like nature. Mineralized remnants of siliceous spicules composed of chemically inert materials are preserved in sedimentary rocks and provide evidence of the ecological state of the ancient biosphere. Sponges occur in waters with low temperatures; therefore, they grow very slowly and live for hundreds of years. The organic silica spicules exhibit the capacity for triboluminescence. The generated light emission may be used by symbiotic bacteria on the spicule surface.     

Preservational modes of some ichthyosaur soft tissues (Reptilia,Ichthyopterygia) from the Jurassic Posidonia Shale of Germany

Konservat-Lagerstätten, such as the Toarcian (Early Jurassic) Posidonia Shale of southwestern Germany, are renowned for their spectacular fossils. Ichthyosaur skeletons recovered from this formation are frequently associated with soft tissues; however, the preserved material ranges from three-dimensional, predominantly phosphatized structures to dark films of mainly organic matter. We examined soft-tissue residues obtained from two ichthyosaur specimens using an integrated ultrastructural and geochemical approach. Our analyses revealed that the superficially-looking ‘films’ in fact comprise sections of densely aggregated melanosome (pigment) organelles sandwiched between phosphatized layers containing fibrous microstructures. We interpret this distinct layering as representing condensed and incompletely degraded integument from both sides of the animal. When compared against previously documented ichthyosaur fossils, it becomes readily apparent that a range of preservational modes exists between presumed ‘phosphatic’ and ‘carbonized’ soft-tissue remains. Some specimens show high structural fidelity (e.g. distinct integumentary layering), while others, including the fossils examined in this study, retain few original anatomical details. This diversity of soft-tissue preservational modes among Posidonia Shale ichthyosaurs offers a unique opportunity to examine different biostratinomic, taphonomic and diagenetic variables that potentially could affect the process of fossilization. It is likely that soft-tissue preservation in the Posidonia Shale was regulated by a multitude of factors, including decay efficiency and speed of phosphatic mineral nucleation; these in turn were governed by a seafloor with sustained microbial mat activity fuelled by high organic matter input and seasonally fluctuating oxygen levels.     

Factors influencing the extent and development of the oxic zone in sediments

Dissolved oxygen concentrations in river-sediment porewaters are reported and modelled using a zero-order reaction rate and the Monod equation. After mixing the sediments and allowing settling, the dissolved oxygen profile in the bed-sediment was expected to reach a steady-state rapidly (< 1 h). However changes in the vertical profile of oxygen over a period of 38 days revealed that the penetration of oxygen increased and the dissolved oxygen flux at the interface decreased with time, probably as the oxidation kinetics of organic matter and redox reactions in the sediment changed. Experiments with three contrasting silt and sand dominated sediments (organic matter content between 0.9 and 18%) at two water velocities (ca 10 and 20 cm s^–1) showed that the dissolved oxygen profiles were independent of velocity for each of the sediments. The most important controls on the reaction rate were the organic matter content and specific surface area of the sediment. A viscous diffuse-boundary-layer above the sediment was only detected in the experiments with the silt sediment where the sediment oxygen demand was relatively high. In the coarser sediments, the absence of a diffuse layer indicated that slow oxidation processes in the sediment controlled the dissolved oxygen flux at the interface. The problem of determining a surface reference in coarse sediment is highlighted. The results are discussed with reference to other studies including those concerned with estuarine and marine sediments.     

Ecosystem responses to increased precipitation and permafrost decay in subarctic Sweden inferred from peat and lake sediments

Recent accelerated decay of discontinuous permafrost at the Stordalen Mire in northern Sweden has been attributed to increased temperature and snow depth, and has caused expansion of wet minerotrophic areas leading to significant changes in carbon cycling in the mire. In order to track these changes through time and evaluate potential forcing mechanisms, this paper analyses a peat succession and a lake sediment sequence from within the mire, providing a record for the last 100 years, and compares these with monitored climate and active layer thickness data. The peat core was analysed for testate amoebae to reconstruct changes in peatland surface moisture conditions and water table fluctuations. The lake sediment core was analysed by near infrared spectroscopy to infer changes in the total organic carbon (TOC) concentration of the lake‐water, and changes in δ¹³C and C, N and δ¹⁵N to track changes in the dissolved inorganic carbon (DIC) pool and the influence of diagenetic effects on sediment organic matter, respectively. Results showed that major shifts towards increased peat surface moisture and TOC concentration of the lake‐water occurred around 1980, one to two decades earlier than a temperature driven increase in active layer thickness. Comparison with monitored temperature and precipitation from a nearby climate station indicates that this change in peat surface moisture is related to June–September (JJAS) precipitation and that the increase in lake‐water TOC concentration reflects an increase in total annual precipitation. A significant depletion in ¹³C of sediment organic matter in the early 1980s probably reflects the effect of a single or a few consecutive years with anomalously high summer precipitation, resulting in elevated DIC content of the lake water, predominantly originating from increased export and subsequent respiration of organic carbon from the mire. Based on these results, it was not possible to link proxy data obtained on peat and lake‐sediment records directly to permafrost decay. Instead our data indicate that increased precipitation and anomalously high rainfall during summers had a significant impact on the mire and the adjacent lake ecosystem. We therefore propose that effects of increased precipitation should be considered when evaluating potential forcing mechanisms of recent changes in carbon cycling in the subarctic.     

Pyrite accumulation in salt marshes in the Eastern Scheldt,southwest Netherlands

Pore water composition, pyrite distribution and pyrite crystal morphology of sediments from salt marshes in the Eastern Scheldt, southwestern Netherlands, were examined from July 1984 to October 1986.Hydrology and marsh vegetation were the chief determinants of pyrite accumulation. In the bare sediments of pans in the low marsh, highly reducing conditions prevailed just below the surface. At these sites, practically all the incoming detrital pyrite (0.5–1% FeS₂) was preserved. The in-situ formation of pyrites was negligible in these anoxic sediments.All incoming detrital pyrite was oxidized in the surface layers (0–10 cm) of the medium-high marsh overgrown withSpartina anglica. Pyrite was formed at a rate of 2.6–3.8 mol S-FeS₂m^–2yr^–1 in a narrow range of depths (15–20cm), at the interface of the oxidizing and underlying reducing sediment. At this interface the concentration profiles of Fe²⁺ and dissolved S intersected. The role of the rhizosphere is discussed in connection with pyrite formation. No further pyrite formation occurred deeper in the sediment. This resulted in the build up of high concentrations of dissolved S and acid volatile sulfides (AVS). The decrease with depth in oxalate-extractable Fe indicated that most of the iron oxyhydroxides (70–80%) had been transformed to pyrite. Another 10–20% of oxalate-extractable Fe was present as AVS. The abundance of framboidal pyrite particles and the high concentrations of AVS and dissolved S indicated that the formation of pyrite occurred via iron monosulfide intermediatesThere was a linear relationship between the organic carbon and the S-FeS₂ content in theSpartina overgrown reducing sediment. The mean C/S ratio was 4.2.     

Algal borings and framboidal pyrite in Upper Ordovician brachiopods

Algal borings in the shells of the articulate brachiopods Plaesiomys subquadrata (Hall) and Hebertella sinuata (Hall) from the Richmond Formation of Ohio are empty, or partially to entirely filled with pyrite. The pyrite occurs as single framboids and other crystal forms, or in chains filling the bores. The borings provide some insight into the early diagenetic history of the Richmond sediments near Cincinnati. Pyritization probably occurred within a few years, only a short distance (a few centimeters) below the sediment surface through the activities of sulfur-reducing bacteria. Pyrite precipitated around a nucleus such as a bacterium or algal cell, or developed within an organic structure such as an algal cell or organic membrane.     

Pyrite in Silurian graptolites from Bornholm, Denmark

Pyrite is present in many horizons in dark grey graptolite-rich shales of Llandovery-early Wenlock age on the island of Bornholm, Denmark. The pyrite usually occurs as internal moulds of the graptolites, but rarely on the outside of the periderm. Occasionally the internal pyrite protrudes from the apertures of the rhabdosomes. Investigations using reflected light and scanning electron microscopy have shown that the internal pyrite is texturally variable. The abundance of the framboids is variable, ranging from thin linings on the inner side of the periderm to nearly complete infills of the graptolite colony. The pyrite also occurs as densely packed microcrystals and as larger euhedral crystals in all transitions from individual crystals, often developed on the surfaces of the framboids. to compact aggregations. Some of the pyritized graptolites have central cavities in the rhabdosomal linings. Within the cavities there are striking stalactite-like forms of pyrite suspended from the roof of the periderm. Some specimens have late infillings by calcite in the central part of the tubes. Most of the internal pyrite must have been formed very early during the taphonomic processes operating on the graptolites, pre-dating the compaction of the sediment. The framboids were first precipitated, followed by the aggregated euhedral pyrite. It is debatable whether the tubes of the graptolites were fluid-filled or partially gas-filled when the stalactites were formed; the latter is the more likely. The beds with fully pyritized graptolites might represent an episodic increase of sedimentation rate and oxygen content of bottom waters. □ Pyrite, Silurian, graptolites, Bornholm, stalactites, early diagenesis.     

Decay and composition of the hemichordate Rhabdopleura: implications for the taphonomy of graptolites

Although the graptolites lacked biomineralised tissue, their skeletons are abundantly preserved in deeper-water mudstones. Decay experiments and observations on the closely related living hemichordate Rhabdopleura demonstrate that the periderm and stolon are highly resistant to decay, remaining intact for months, whereas the zooids are unrecognizable within days. The extreme rarity of the preservation of traces of the zooids in graptoloids reflects their planktic lifestyle; the zooids had normally decayed before burial. Curie-point-gas-chromatography (Py-GC) and Curie-point-gas-chromatography-mass spectrometry (Py-GC-MS) of the periderm of Rhabdopleura confirms that proteinaceous organic matter is a major constituent. Ultrastructurally preserved graptolite periderm (Ordovician, Oklahoma; Silurian, Arctic Canada), on the other hand, is a highly altered kerogen-like substance rich in aliphatic biomacromolecules. The composition of the preserved graptolite periderm reflects diagenetic replacement by components probably mainly derived from algal cell walls.     

Palaeoceanographic redox environments for the lower Cambrian Hetang Formation in South China: Evidence from pyrite framboids,redox sensitive trace elements,and sponge biota occurrence

The lower Cambrian Hetang Formation, a black shale sequence, contains a stone coal (a flammable, organic-rich mudstone) unit. Abundant pyrite framboids occur in this unit, with the average mean sizes falling in a narrow range from 4.6 to 5.4 μm and the maximum diameters being around 10 μm. The size distribution pattern of the pyrite framboids indicates a euxinic depositional environment. The redox-sensitive trace metals of the stone coal samples reveal a large enrichment of Mo (10–180 times),V (4–40 times), U (10–60 times) and Ni (2–20 times) compared to the average upper continental crust value, consistent with an anoxic environment for their deposition. The redox-sensitive element ratios (Th/U, V/(V + Ni), V/Cr) indicate that the depositional environment for the lower part of the stone coal unit was the most anoxic and euxinic. In contrast, a sponge biota including eleven species of demosponges and hexactinellids and two undetermined forms indicate an oxic or dysoxic environment. To reconcile these two facts, we propose that although an anoxic/euxinic environment predominated during the deposition of the lower Cambrian Hetang Formation black shales, occasional currents may also have brought free oxygen to the bottom water column to allow the growth of the sponges on the sea floor.     

Organic matter diagenesis at the oxic/anoxic interface in coastal marine sediments,with emphasis on the role of burrowing animals

The present paper reviews the current knowledge on diagenetic carbon transformations at the oxic/anoxic interface in coastal marine sediments. Oxygen microelectrodes have revealed that most coastal sediments are covered only by a thin oxic surface layer. The penetration depth of oxygen into sediments is controlled by the balance between downward transport and consumption processes. Consumption of oxygen is directly or indirectly caused by respiration of benthic organisms. Aerobic organisms have the enzymatic capacity for complete oxidation of organic carbon. Anaerobic decay occurs stepwise, involving several types of bacteria. Large organic molecules are first fermented into small moieties. These are then oxidized completely by anaerobic respirers using a sequence of electron acceptors: Mn⁴⁺, NO₃ ^-, Fe³⁺, SO₄ ^2- and CO₂. The quantitative role of each electron acceptor depends on the sediment type and water depth. Since most of the sediment oxygen uptake is due to reoxidation of reduced metabolites, aerobic respiration is of limited importance. It has been suggested that sediments contain three major organic fractions: (1) fresh material that is oxidized regardless of oxygen conditions; (2) oxygen sensitive material that is only degraded in the presence of oxygen; and (3) totally refractory organic matter. Processes occurring at the oxic/anoxic boundaries are controlled by a number of factors. The most important are: (1) temperature, (2) organic supply, (3) light, (4) water currents, and (5) bioturbation. The role of bioturbation is important because the infauna creates a three-dimensional mosaic of oxic/anoxic interfaces in sediments. The volume of oxic burrow walls may be several times the volume of oxic surface sediment. The infauna increases the capacity, but not the overall organic matter decay in sediments, thus decreasing the pool of reactive organic matter. The increase in decay capacity is partly caused by injection of oxygen into the sediment, and thereby enhancing the decay of old, oxygen sensitive organic matter several fold. Finally, some future research directions to improve our understanding of diagenetic processes at the oxic/anoxic interface are suggested.     

Pseudofossils in relict methane seep carbonates resemble endemic microbial consortia

Pleistocene-age methane seep carbonates from the Eel River Basin, California contain aggregate-like structures composed of tightly-packed hollow spheres that morphologically resemble syntrophic archaeal–bacterial consortia known to catalyze the anaerobic oxidation of methane (AOM). Tetragonal microstructures also present in the carbonates resemble seep-endemic Methanosarcinales cell clusters. Despite morphological similarities to the seep-endemic microbes that likely mediated the authigenesis of Eel River Basin carbonates and sulfides, detailed petrographic, SEM, and magnetic microscopic imaging, remanence rock magnetism, laser Raman, and energy dispersive X-ray spectroscopy, suggest that these microstructures are not microfossils, but rather mineral structures that result from the diagenetic alteration of euhedral Fe-sulfide framboids. Electron microscopy shows that during diagenesis, reaction rims composed of Fe oxide form around framboid microcrystalites. Subsequent dissolution of greigite or pyrite crystals leaves behind hollow cell-like casings (external molds) — a transformation that occurs on timescales of ～100 kyr or less. Despite their superficial resemblance to morphologically-distinctive extant microbes in local sediments, the presence of acellular precursor grains, as well as of partially-altered transitional forms, complicate the interpretation of these and other framboidal microstructures that have been reported from the rock record.     

Redox conditions during sedimentation of the Middle Jurassic (Upper Bajocian–Bathonian) clays of the Polish Jura (south-central Poland)

Depositional redox conditions of the uppermost Bajocian–Bathonian (Middle Jurassic) ore-bearing clays of the Gnaszyn/Kawodrza area in the Polish Jura have been determined using an integrated geochemical (Th/U and U/Th ratios, degree of pyritisation (DOP), sulphur stable isotopes, biomarker analysis) and petrographic approach (measurements of pyrite framboid diameters, and microfacies analysis). The Th/U and U/Th ratios indicate that oxic conditions prevailed on the sea-floor during this interval, and ³⁴S isotopes suggest open-system conditions. DOP values, however, are rather scattered, and may reflect oxic, dysoxic, or anoxic conditions. We consider that the DOP values result from reducing conditions within the sediment and the chemistry of the pore-waters, rather than true sea-floor redox conditions. Pyrite framboid populations also indicate that dysoxic conditions prevailed within the sediment, beneath an oxygenated water column. Biomarker data did not provide any evidence of water column stratification or anoxia during sedimentation of the Middle Jurassic clays.     

Arctic sediments (Svalbard): pore water and solid phase distributions of C,N, P and Si

Pore water and solid phase distributions of C, N, P and Si in sediments of the Arctic Ocean (Svalbard area) have been investigated. Concentrations of organic carbon (C_org) in the solid phase of the sediment varied from 1.3 to 2.8% (mean 1.9%), with highest concentrations found at shallow stations south/southwest of Svalbard. Relatively low concentrations were obtained at the deeper stations north/northeast of Svalbard. Atomic carbon to nitrogen ratios in the surface sediment ranged from below 8 to above 10. For some stations, high C/N ratios together with high concentrations of C_org suggest that sedimentary organic matter is mainly of terrigenous origin and not from overall biological activity in the water column. Organic matter reactivity (defined as the total sediment oxygen consumption rate normalized to the organic carbon content of the surface sediment) correlated with water depth at all investigated stations. However, the stations could be divided into two separate groups with different reactivity characteristics, representing the two most dominant hydrographic regimes: the region west of Svalbard mainly influenced by the West Spitsbergen Current, and the area east of Svalbard where Arctic polar water set the environmental conditions. Decreasing sediment reactivity with water depth was confirmed by the partitioning between organic and inorganic carbon of the surface sediment. The ratio between organic and inorganic carbon at the sediment-water interface decreased exponentially with water depth: from indefinite values at shallow stations in the central Barents Sea, to approximately 1 at deep stations north of Svalbard. At stations east of Svalbard there was an inverse linear correlation between the organic matter reactivity (as defined above) and concentration of dissolved organic carbon (DOC) in the pore water. The more reactive the sediment, the less DOC existed in the pore water and the more total carbonate (C_t or ΣCO₂) was present. This observation suggests that DOC produced in reactive sediments is easily metabolizable to CO₂. Sediment accumulation rates of opaline silica ranged from 0.35 to 5.7 μmol SiO₂ m⁻²d⁻¹ (mean 1.3 μmol SiO₂ m⁻²d⁻¹), i.e. almost 300 times lower than rates previously reported for the Ross Sea, Antarctica. Concentrations of ammonium and nitrate in the pore water at the sediment-water interface were related to organic matter input and water depth. In shallow regions with highly reactive organic matter, a pool of ammonium was present in the pore water, while nitrate conoentrations were low. In areas where less reactive organic matter was deposited at the sediment surface, the deeper zone of nitrification caused a build-up of nitrate in the pore water while ammonium was almost depleted. Nitrate penetrated from 1.8 to ≥ 5.8 cm into the investigated sediments. Significantly higher concentrations of “total” dissolved nitrogen (defined as the sum of NO₃, NO₂, NH₄ and urea) in sediment pore water were found west compared to east of Svalbard. The differences in organic matter reactivity, as well as in pore water distribution patterns of “total” dissolved nitrogen between the two areas, probably reflect hydrographic factors (such as ice coverage and production/import of particulate organic material) related to the dominant water mass (Atlantic or Arctic Polar) in each of the two areas. The data presented were collected during the European “Polarstern” Study (Arctic EPOS) sponsored by the European Science Foundation     

Sediment Chemistry of Lake Bhim Tal,U. P., India

Certain chemical constituents (NO₃-N, bio-available P, Ca, Na, K, Mn, Cu, Co and organic matter) together with pH, Eh and clay content of surface sediments at various depths of the overlying water in Lake Bhim Tal were examined during 1977—1978. In addition, NH₃-N and dissolved oxygen at the mud-water interface (water immediately above the sediments) were measured. The values of Eh, pH and NO₃-N in the sediments showed a negative relationship with water depth and positive relationship with dissolved oxygen at the interface. The other variables of the sediment were positively related to water depth and negatively related to dissolved oxygen at the interface. Organic matter, K, Na and Ca showed positive relationship with the amount of clay while the cations (K, Na, Ca) and trace metals (Cu, Mn, Co) showed a positive relationship with the amount of organic matter in the sediments.