1. Suspended particle property variation in Gaoping Submarine Canyon Ray T. Hsu and James T. Liu Institute of Marine Geology and Chemistry, National Sun Yat-sen University, Kaohsiung, Taiwan, 804 Salinity (psu) Julian day (2006) Introduction The hydrographic environment in submarine canyons is highly dynamic that affects the physical properties of suspended particles in the water column. Some parameters relating to the behavior and nature of the suspended matter such as the insitu particle size distribution, density, and settling velocity are of interest to oceanographers. Gaoping River 8/27-28/2006 Gaoping Submarine Canyon Taiwan Strait 6/18/2004 Method and study area Two cruises were conducted on June 18, 2004 and August 27-28, 2006 for hourly CTD profiling with LISST-100 attached and water samples collection at different depths in the Kaoping Submarine Canyon off southwestern Taiwan. In the 2004 cruise, 10 L of water samples were filtered sequentially through two stainless steel sieves (mesh size of 500 and 250 μm), two nylon mesh nets (63 and 10 μm), and finally the GF/C filter (0.4 μm) in the lab. A new-stacked filtering system, CatNet, filtered 60 L water samples on board through 153, 63, and 10 μm stacked nylon nets. The residual filtered water filled up a 20 L plastic container and filtered through 2.7 and 0.7 μm filters in the lab. All filtered particles were dried in the oven at 50 °C and then weighed rendering suspended sediment concentration (SSC) in mg/l. Results and discussion According to time serious salinity profile (left figure), the effluent river plume was on the sea surface thin layer, of which thickness was less than 10 m. The salinity profiles was indicated that the strong fresh water signal was stronger since 7:00 to 9:00 am on 6/28, 2006. The mean diameter of suspended particles in the water column was calculated from LISST-100 profile data. Profiles of particle mean size showed fluctuation vertically and temporally. The surface grain mean size varied around 60  m. However, particle mean size significantly increased over 100  m in the surface layer during low salinity period. This trend implied that there were larger suspended particles in the fresher plume water. Before and after the low surface salinity period (from 19:01 on 6/27 to 01:59 on 6/28, and 12:28 to 13:28 on 6/28), particle size increased before the event and then decreased after the event. The actual mechanism are unknown. Floc porosity and density profiles: Base on the Krone’s model, we suggested a new method to evaluate the in situ bulk floc density of different particle-size classes. The concluding bulk density of this new estimation was similar to the literature presented. The floc density of three grain-size classes indicated that the smaller the size, the higher the density. The floc density profile showed a maximum at the middle depth around 150 m and decreased toward the surface and bottom layer. Conclusions In this investigation, the physical properties of suspended particles in Gaoping Submarine Canyon highly varied in the vertical water column. It is suggested that high dynamic environment will change the suspended particle properties, such as mean particle size and density. The relationships between suspended particle properties variations and in situ hydrodynamics will be further analyzed. Acknowledgement This research was funded by National Science Council under the no. NSC 93-2611-M-110-013 and NSC 95-2745-M- 110-001 in Taiwan, R.O.C.