Sea Sediments (sea + sediment)

Distribution by Scientific Domains

Kinds of Sea Sediments

  • baltic sea sediment

  • Selected Abstracts

    Remobilization of Polychlorinated Biphenyl from Baltic Sea Sediment: Comparing the Roles of Bioturbation and Physical Resuspension

    Jenny E. Hedman
    Abstract The release of a 14C-labeled trichlorobiphenyl compound ([14C]PCB 32) from sediment to water was quantified weekly in a 30-d microcosm experiment with recirculating water. Two modes of bioturbation-driven polychlorinated biphenyl (PCB) release,bioturbation by the amphipod Monoporeia affinis (a particle biodiffuser) and bioturbation by the polychaete Marenzelleria sp. (a bioirrigator),were compared to the PCB release caused by physical resuspension of the sediment generated by a motor-driven paddle used twice a week. Bioturbation by the amphipod M. affinis caused a significantly higher remobilization of both particle-associated PCB (PCBpart) and dissolved PCB (PCBdiss) than the other treatments. Bioturbation by Marenzelleria sp. and physical resuspension caused a similar release of PCBdiss despite a significantly higher amount of total suspended solids in the water column after physical resuspension. In all treatments, the release of PCBdiss was more than one order of magnitude higher than that of PCBpart, indicating a significant potential route of exposure for pelagic organisms, such as fish, to the most bioavailable PCB form. Calculated mass-transfer coefficients (0.3,1.3 cm/d) correspond to previously reported values for trichlorinated PCBs. The present results indicate that biological reworking of sediments can be just as, or even more, important than physical resuspension for the remobilization of sediment-bound contaminants. [source]

    Active bacterial community structure along vertical redox gradients in Baltic Sea sediment

    Anna Edlund
    Summary Community structures of active bacterial populations were investigated along a vertical redox profile in coastal Baltic Sea sediments by terminal-restriction fragment length polymorphism (T-RFLP) and clone library analysis. According to correspondence analysis of T-RFLP results and sequencing of cloned 16S rRNA genes, the microbial community structures at three redox depths (179, ,64 and ,337 mV) differed significantly. The bacterial communities in the community DNA differed from those in bromodeoxyuridine (BrdU)-labelled DNA, indicating that the growing members of the community that incorporated BrdU were not necessarily the most dominant members. The structures of the actively growing bacterial communities were most strongly correlated to organic carbon followed by total nitrogen and redox potentials. Bacterial identification by sequencing of 16S rRNA genes from clones of BrdU-labelled DNA and DNA from reverse transcription polymerase chain reaction showed that bacterial taxa involved in nitrogen and sulfur cycling were metabolically active along the redox profiles. Several sequences had low similarities to previously detected sequences, indicating that novel lineages of bacteria are present in Baltic Sea sediments. Also, a high number of different 16S rRNA gene sequences representing different phyla were detected at all sampling depths. [source]

    A thermodynamic analysis of the anaerobic oxidation of methane in marine sediments

    GEOBIOLOGY, Issue 5 2008
    D. E. LAROWE
    ABSTRACT Anaerobic oxidation of methane (AOM) in anoxic marine sediments is a significant process in the global methane cycle, yet little is known about the role of bulk composition, temperature and pressure on the overall energetics of this process. To better understand the biogeochemistry of AOM, we have calculated and compared the energetics of a number of candidate reactions that microorganisms catalyse during the anaerobic oxidation of methane in (i) a coastal lagoon (Cape Lookout Bight, USA), (ii) the deep Black Sea, and (iii) a deep-sea hydrothermal system (Guaymas basin, Gulf of California). Depending on the metabolic pathway and the environment considered, the amount of energy available to the microorganisms varies from 0 to 184 kJ mol,1. At each site, the reactions in which methane is either oxidized to , acetate or formate are generally only favoured under a narrow range of pressure, temperature and solution composition , particularly under low (10,10 m) hydrogen concentrations. In contrast, the reactions involving sulfate reduction with H2, formate and acetate as electron donors are nearly always thermodynamically favoured. Furthermore, the energetics of ATP synthesis was quantified per mole of methane oxidized. Depending on depth, between 0.4 and 0.6 mol of ATP (mol CH4),1 was produced in the Black Sea sediments. The largest potential productivity of 0.7 mol of ATP (mol CH4),1 was calculated for Guaymas Basin, while the lowest values were predicted at Cape Lookout Bight. The approach used in this study leads to a better understanding of the environmental controls on the energetics of AOM. [source]

    Deglaciation of the Irish Sea Basin: a critique of the glaciomarine hypothesis

    Danny McCarroll
    Abstract The glaciomarine model for deglaciation of the Irish Sea basin suggests that the weight of ice at the last glacial maximum was sufficient to raise relative sea-levels far above their present height, destabilising the ice margin and causing rapid deglaciation. Glacigenic deposits throughout the basin have been interpreted as glaciomarine. The six main lines of evidence on which the hypothesis rests (sedimentology, deformation structures, delta deposits, marine fauna, amino-acid ratios and radiocarbon dates) are reviewed critically. The sedimentological interpretation of many sections has been challenged and it is argued that subglacial sediments are common rather than rare and that there is widespread evidence of glaciotectonism. Density-driven deformation associated with waterlain sediments is rare and occurs where water was ponded locally. Sand and gravel deposits interpreted as Gilbert-type deltas are similarly the result of local ponding or occur where glaciers from different source areas uncoupled. They do not record past sea-levels and the ad hoc theory of ,piano-key tectonics' is not required to explain the irregular pattern of altitudes. The cold-water foraminifers interpreted as in situ are regarded as reworked from Irish Sea sediments that accumulated during much of the late Quaternary, when the basin was cold and shallow with reduced salinities. Amino-acid age estimates used in support of the glaciomarine model are regarded as unreliable. Radiocarbon dates from distinctive foraminiferal assemblages in northeast Ireland show that glaciomarine sediments do occur above present sea-level, but they are restricted to low altitudes in the north of the basin and record a rise rather than a fall in sea-level. It is suggested here that the oldest dates, around 17 000 yr BP, record the first Late Devensian (Weichselian) marine inundation above present sea-level. This accords with the pattern but not the detail of recent models of sea-level change. Copyright 2001 John Wiley & Sons, Ltd. [source]

    Debris flow and slide deposits at the top of the Internal Liguride ophiolitic sequence, Northern Apennines, Italy: A record of frontal tectonic erosion in a fossil accretionary wedge

    ISLAND ARC, Issue 1 2001
    Michele Marroni
    Abstract In the Northern Apennines, the Internal Liguride units are characterized by an ophiolite sequence that represents the stratigraphic base of a late Jurassic,early Paleocene sedimentary cover. The Bocco Shale represents the youngest deposit recognized in the sedimentary cover of the ophiolite and can be subdivided into two different groups of deep sea sediments. The first group is represented by slide, debris flow and high density turbidity current-derived deposits, whereas the second group consists of thin-bedded turbidites. Facies analysis and provenance studies indicate, for the former group, small and scarcely evoluted flows that rework an oceanic lithosphere and its sedimentary cover. We interpret the Bocco Shale as an ancient example of a deposit related to the frontal tectonic erosion of the accretionary wedge slope. The frontal tectonic erosion resulted in a large removal of materials, from the accretionary wedge front, that was reworked as debris flows and slide deposits sedimented on the lower plate above the trench deposits. The frontal tectonic erosion was probably connected with subduction of oceanic crust characterized by positive topographic relief. This interpretation can be also applied for the origin of analogous deposits of Western Alps and Corsica. [source]