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  • 2000-2004  (6)
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  • 1
    Online Resource
    Online Resource
    Pore-water advection and organic matter mineralization in North Sea shelf sands (2004)
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    Keywords: Hochschulschrift
    Description / Table of Contents: Continental shelf, North Sea, sand, sediment, pore-water advection, oxygen, nutrients, solute flux, organic matter, mineralization, sediment surface topography, currents, benthic chamber. - Advective pore-water transport and its effect on sediment metabolism was studied in sandy sediments north of the Island of Spiekeroog in situ. Natural pressure gradients as estimated from sediment topography and bottom flow indicated significant advection in medium and coarse sands. This was confirmed by time series of oxygen micro profiles, showing an advective supply of oxygen to the sediment. The contribution of this supply to the sediment oxygen uptake was investigated with benthic chambers that exposed the enclosed sediments to defined pressure gradients to induce pore-water advection at natural rates. At high permeabilities the oxygen uptake increased significantly in the presence of advection, indicating its potential to favor aerobic degradation of organic matter in permeable sands. Combining these measurements with larger scale estimates of sediment permeabilities, pore-water advection was expected to promote sediment oxygen consumption in up to 60 % of the German Bight area.
    Type of Medium: Online Resource
    Pages: Online-Ressource (Text + images, 2711 Kb = 189 p.)
    URL: http://nbn-resolving.de/urn:nbn:de:gbv:46-diss000101769
    DDC: 551.46861336
    Language: English
    Note: Bremen, Univ., Diss., 2004
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  • 2
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    Metabolism and decompression tolerance of scavenging lysianassoid deep-sea amphipods (2002)
    In:  EPIC3Deep Sea Research Part I: Oceanographic Research Papers, 49(7), pp. 1281-1289, ISSN: 09670637
    Details
    Publication Date: 2017-03-06
    Description: Respiration, ammonia excretion and decompression tolerance were studied in several species of lysianassoid amphipods captured at four stations in the deep Arabian Sea with an isolated trap maintaining them at in situ temperature. The amphipods were decompressed from their ambient to atmospheric pressure during recovery. Six amphipods, belonging to the species Eurythenes gryllus, Paralicella caperesca and Abyssorchomene abyssorum, survived decompression from depths between 1920 and 4420 m. The physiological condition of these specimens was good inferred by the fact that their swimming and resting behaviour appeared normal, they reacted to disturbance by light and vibration, and were able to ingest food to maintain full guts. Most of the amphipods (421 individuals), however, were recovered dead, which allows information about their decompression tolerance and their vertical migration ability to be deduced. Weight-specific respiration rates of the deep-sea amphipods that were fed prior to the experiments were not lower than in shallow-water amphipods living at similar temperatures. Differences in respiration rates between the specimens are discussed with regard to body size, species specificity and food supply. Weight-specific ammonia excretion rates were extremely high when compared with shallow-water relatives, indicating a capability for rapid digestion. This may be an adaptation to the unpredictable food supply in the deep sea as it enables the amphipod to empty its digestive tract quickly, thus making it available for additional food. Rapid digestion also enables the animals to regain mobility soon after feeding, permitting them to move to new food sources.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
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    Decomposition of diatoms and nutrient dynamics in permeable North Sea sediments (2004)
    In:  EPIC3Continental Shelf Research, 24(6), pp. 721-737, ISSN: 02784343
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    Publication Date: 2017-03-06
    Description: This study addresses the decomposition of diatoms in different permeable North Sea sand beds. During three cruises in 2001 to the southern German Bight, the regeneration of nutrients was assessed after the experimental deposition of organic matter corresponding to a typical spring diatom bloom in in situ and on-board chamber experiments. The diatom pulse was followed by a high regeneration of nutrients during the first day: 5–10% d−1 of the added nitrogen was converted to NH4+ and up to 0.67% d−1 of the added biogenic silica was dissolved to Si(OH)4. These results are used to interpret the response of pore water nutrient concentrations in permeable North Sea sands to seasonal nutrient and phytoplankton dynamics in the water column. The rapid advective solute exchange in these permeable sediments reduces the accumulation of regenerated nutrients, and, thus pore water concentrations of Si(OH)4, PO43− and NH4+ decreased with increasing permeability. All sands were characterized by relatively high NO3− concentrations down to 10 cm sediment depth, indicating that the upper sediment layers are oxidized by advective flushing of the bed. Our results demonstrate that biogenic silica and organic matter are rapidly degraded in permeable coastal sands, revealing that these sediments are very active sites of nutrient recycling.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    Benthic biogeochemistry: state of the art technologies and guidelines for the future of in situ survey (2003)
    In:  EPIC3Journal of Experimental Marine Biology and Ecology, 285-28, pp. 5-31, ISSN: 00220981
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    Publication Date: 2017-03-06
    Description: Sediment and water can potentially be altered, chemically, physically and biologically as they are sampled at the seafloor, brought to the surface, processed and analysed. As a result, in situ observations of relatively undisturbed systems have become the goal of a growing body of scientists. Our understanding of sediment biogeochemistry and exchange fluxes was revolutionized by the introduction of benthic chambers and in situ micro-electrode profilers that allow for the direct measurement of chemical fluxes between sediment and water at the sea floor and for porewater composition. Since then, rapid progress in the technology of in situ sensors and benthic chambers (such as the introduction of gel probes, voltammetric electrodes or one- and two-dimensional optodes) have yielded major breakthroughs in the scientific understanding of benthic biogeochemistry. This paper is a synthesis of discussions held during the workshop on sediment biogeochemistry at the “Benthic Dynamics: in situ surveillance of the sediment–water interface” international conference (Aberdeen, UK—March 25–29, 2002). We present a review of existing in situ technologies for the study of benthic biogeochemistry dynamics and related scientific applications. Limitations and possible improvement (e.g., technology coupling) of these technologies and future development of new sensors are discussed. There are countless important scientific and technical issues that lend themselves to investigation using in situ benthic biogeochemical assessment. While the increasing availability of these tools will lead research in yet unanticipated directions, a few emerging issues include greater insight into the controls on organic matter (OM) mineralization, better models for the understanding of benthic fluxes to reconcile microelectrode and larger-scale chamber measurements, insight into the impacts of redox changes on trace metal behavior, new insights into geochemical reaction pathways in surface sediments, and a better understanding of contaminant fate in nearshore sediments.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
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    Scavenger assemblages under differing trophic conditions: a case study in the deep Arabian Sea (2000)
    In:  EPIC3Deep Sea Research Part II: Topical Studies in Oceanography, 47(14), pp. 2999-3026, ISSN: 09670645
    Details
    Publication Date: 2017-03-06
    Description: Baited cameras and traps were deployed at four stations in the deep Arabian Sea to investigate the composition of the necrophagous fauna and to evaluate whether regional differences in trophic conditions are reflected by differing scavenger assemblages. The ophidiid fish Barathrites iris, the large lysianassoid amphipod Eurythenes gryllus, the aristeid prawn Plesiopenaeus armatus, and zoarcid fishes of the genus Pachycara were abundant at the bait at all stations. The ophidiid Holcomycteronus aequatorius, the liparid fish Paraliparis sp., and galatheid crabs of the genus Munidopsis occurred in considerable numbers at single sites. Trap catches further contained lysianassoid amphipods of the genera Paralicella, Abyssorchomene and Paracallisoma. In contrast to scavenger assemblages of the Atlantic and Pacific Ocean, macrourid fishes were virtually absent at the bait. E. gryllus and B. iris consumed the main proportion of the bait, while consumption was at most moderate in all other taxa. Feeding strategies of the respective taxa are inferred from their behavior at the bait and discussed with regard to the profit that can be drawn from food falls. Differences between stations were pronounced with respect to species dominating bait consumption. E. gryllus appeared in highest numbers at the bait in the productive northern and central Arabian Sea where a relatively high availability of food items is expected to sustain high population densities. High numbers of B. iris in the least productive southern part indicate their ability to persist under food-poor conditions and may correspond to a high dependency on food falls. E. gryllus and B. iris both occurred in smaller numbers in the particularly productive western Arabian Sea. This may reflect a reduced dependency on food falls, due to an access to alternative food sources, rather than small population densities. Smaller numbers of E. gryllus and B. iris resulted in slower bait consumption and gave Pachycara spp. the opportunity to contribute considerably to bait consumption. The relation between scavenger assemblages and trophic conditions is discussed with respect to results obtained under differing trophic regimes in the Atlantic and Pacific Ocean.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
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    Oxygen uptake by aquatic sediments measured with a novel non-invasive eddy-correlation technique (2003)
    In:  EPIC3Marine Ecology Progress Series, 261, pp. 75-83, ISSN: 0171-8630
    Details
    Publication Date: 2017-03-06
    Description: This paper presents a new non-invasive technique for measuring sediment O2 uptake that, in its concept, differs fundamentally from other methods used to date. In almost all natural aquatic environments, the vertical transport of O2 through the water column toward the sediment surface is facilitated by turbulent motion. The new technique relies on measuring 2 parameters simultaneously and at the same point in the water above the sediment: the fluctuating vertical velocity using an acoustic Doppler velocimeter and the fluctuating O2 concentration using an O2 microelectrode. From these 2 parameters, which typically are measured 10 to 50 cm above the sediment surface for a period of 10 to 20 min and at a frequency of 15 to 25 Hz, the vertical flux of O2 toward the sediment surface is derived. Based on measurements performed under actual field conditions and comparisons with in situ flux-chamber measurements, we believe that this new technique is the optimal approach for determining O2 uptake by sediments. The technique is superior to conventional methods as measurements are done under true in situ conditions, i.e. without any disturbance of the sediment and under the natural hydrodynamic conditions. Furthermore, this technique can be used for bio-irrigated or highly permeable sediments, such as sands, where traditional methods often fail. While this paper only focuses on O2 uptake by sediments, the technique can also be applied to other solutes that can be measured at a sufficiently high temporal resolution.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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