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Sediment Dynamics and Morphodynamics of River-Sea Sediment Dispersal Systems through Space and Time: A Source-to-Sink Perspective
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Identification of diverse particle types in the water column on the Gaoping shelf, SW Taiwan
P-G1-02-S
Peter Z. Jue* , Department of Oceanography, National Sun Yat-sen University, Kaohsiung, Taiwan
James T. Liu, Department of Oceanography, National Sun Yat-sen University, Kaohsiung, Taiwan
Presenter Email: legendstory0129@gmail.com |
| With the progress of science and technology, LISST-Holo can provide us particle images, which is a laser camera, whose advantage is to generate holograms of in-situ particles. We can use the programs released by the manufacturer Sequoia to reconstruct images and get statistics on particle data. With reconstructed images, we can classify particles into biogenic and floc categories and measure particle sizes easily. The strength of incorporating this brand-new instrument into particle research is Holo can avoid breaking fragile flocs into pieces during water sample collection and the ensuing filtering procedure.
This study was conducted on board R/V Ocean Researcher III on the OR3-2039 cruise on November 11th, 2017. The field work was to observe particles in the water column off Gaoping area. In our field experiment, LISST-Holo was placed on the CTD Rossette and stopped at five depths (5, 20, 50, 100, 160 m) for at least two minutes each time to collect the enough samples due to the low sample frequency (0.2 Hz). In order to fit the limit on the moving speed of LISST Holo, we kept the CTD at the casting rate of 0.5 m/s. In addition to hologram data, we also collected water samples to analyze suspended sediment concentration (SSC) and chlorophyll-a. We used these data to examine the distribution of particles and their types at the study site.
Until now, our findings from holograms show there were more zooplankton and phytoplankton in surface water than bottom water because of enough sunlight. The number of biogenic particles in the bottom was almost zero. The biogenic particles we found were diatoms, radiolarians, dinoflagellates, etc. On the other hand, flocs were present both in surface and bottom waters, but there were more flocs in the bottom. We also measured SSC corresponding to chlorophyll-a shallower than 45 m. The percentages of biogenic particles at each depth LISST-Holo measured were 89% (at 5 m) and 55% (at 20 m). The trend of SSC and chlorophyll-a were opposite in depths deeper than 45 m. With the increasing depth, chlorophyll-a concentration decreased, and SSC increased. The percentages of flocs were 74% (at 50 m), 97% (at 100 m), and 100% (at 160 m). As a result, we suggest the change of SSC shallower than the 45 m depth was dominated by biogenic particles, and the change deeper than 45 m was dominated by flocs.
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