Title page for etd-0906102-183200


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URN etd-0906102-183200
Author Hui-Chen Chang
Author's Email Address No Public.
Statistics This thesis had been viewed 5342 times. Download 1603 times.
Department Marine Geology and chemistry
Year 2001
Semester 2
Degree Master
Type of Document
Language zh-TW.Big5 Chinese
Title Settling Particulates and Sediments in the Northern South China Sea: Distributions of Mass Flux and Pb-210
Date of Defense 2002-07-29
Page Count 64
Keyword
  • flux
  • Pb-210
  • Settling Particulates
  • Northern South China Sea
  • Abstract This study reports the first sediment trap mooring results obtained
    under the SIBEX program (South China Sea Integrated Biogeochemical
    Experiments). Two strings of sediment traps were deployed respectively
    at M1 located to the southwest of Taiwan, and M2 in the northern basin
    of the South China Sea (SCS). Box cores were also taken at several
    sites to the south of M2. The main purposes are to measure settling
    particulate fluxes at various depths for the studies of temporal and spatial
    variations of the particulate flux and 210Pb activity. The box cores were
    used to determine the sedimentation rates. These are to enhance our
    understanding of the characteristics of the particulate distribution and the
    roles the particulate matter plays in the biogeochemical processes in the
    SCS.
    Particulate fluxes measured from different depths at M1 and M2
    generally increase with depth. In temporal variation, M1 has higher
    amplitudes than M2, with highest amplitudes at 948 m where highest flux
    (2025 mg/m2/d) was observed. The particulate flux at 948 m has higher
    values than at 248 m, probably due to lateral transport. At M2, the
    particulate flux at 240 m has higher values with greater amplitudes than at
    greater depths, i.e. 1240 m, 2240 m and 3240 m, where their particulate
    fluxes show a synchronous trend with small amplitudes in temporal
    variation. The time-averaged particulate flux for each trap ranges from
    199 to 554 mg/m2/d, consistently higher than previous observations
    (76~104 mg/m2/d). However, our values are comparable to the mean
    particulate flux (280 mg/m2/d) estimated from terrigenous inputs. The
    apparent changes in particulate flux in the SCS over the past ten years
    warrants further investigations.
    The temporal variations of Pb-210 show a synchronous trend and a
    rapid increase with depth as observed at M1 and M2. This rapid
    increase of Pb-210 with depth reflects effective scavenging by sinking
    particulates although particulate concentrations are low. The loss on
    ignition (L.O.I.) at M1 and M2 was inversely correlated with Pb-210,
    indicating that Pb-210 was expelled from biogenic particulates or organic
    matter. The particulate fluxes around 240 m at M1 and M2 were
    generally positively correlated with the L.O.I., suggesting that the high
    particulate fluxes are probably contributed by biogenic particulates or
    organic matter.
    The sedimentation rates as determined from excess Pb-210 profiles
    range from 9.01~23.13 cm/100yr. These rapid sedimentation rates
    reflect the effect of mixing and additional sediments accumulated through
    lateral transport. The surface layers of these cores were subject to
    perturbation and mixing, based on the penetration depths of the excess
    Pb-210. The Pb-210 flux estimated from the inventory of excess Pb-210
    in the sediments is much greater than that observed from the traps,
    suggesting that additional Pb-210 has been accumulated via lateral
    transport and slumping of nearby surface sediments. Based on the mean
    particulate flux observed, one may roughly estimate the corresponding
    sedimentation rate of about 10 cm/ka, which is an order of magnitude
    lower than those determined by the excess Pb-210 method. Because the
    upper layers of the sediments have been strongly disturbed and mixed
    with the additional sediments accumulated through lateral transport, the
    sedimentation rates as determined by the excess Pb-210 method are
    probably over-estimated by a factor of 10 to 20.
    Advisory Committee
  • none - chair
  • none - co-chair
  • Yu-chia Chung - advisor
  • Files
  • etd-0906102-183200.pdf
  • indicate access worldwide
    Date of Submission 2002-09-06

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