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.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0906102-183200 |
| Date | 06 September 2002 |
| Creators | Chang, Hui-Chen |
| Contributors | Yu-chia Chung, none, none |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0906102-183200 |
| Rights | unrestricted, Copyright information available at source archive |
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