Suspended particle property variations in Gaoping Submarine Canyon Ray T. Hsu and James T. Liu Institute of Marine Geology and Chemistry, National Sun Yat-sen University, Kaohsiung, Taiwan, R.O.C.

Gaoping river-sea system Estuarine system: River plume Biogenic production Flocculation & deflocculation Canyon Channel: Landslides Debris flows Turbidity current Nepheloid layers Shelf Region: Biogenic production Resuspension

Particle settling Internal tide Shelf margin C. Benthic nepheloid layer A. Hypopycnal plume B. Hyperpycnal plume

Diversities of suspended particles in coastal water > 500 μm > 63 μm > 250 μm > 10 μm Optical microscopy

Study area Gaoping River 8/27-28/2006 Gaoping Submarine Canyon Taiwan Strait 6/18/2004

Investigation scheme Date 6/18/20048/27-28/2006 Water Sampling Sampling Periods 8 Hours24 Hours Sampling intervals 1 HourAbout 3 hours Sampling volume 10 L at 6 different depths 60 L (at 20 m and 15 m above bed) Number of profiling 168 CTD and LISST-100 profiling Sampling intervals 1 HourAbout 1 hour

500 µm stainless steel sieve 250 µm stainless steel sieve 63 µm nylon net 10 µm nylon net 10 L water sample 3 µm 0.7 µm 2004/6/18 cruise2006/8/27-28 cruise  All filtered particles were dried in the oven at 50 ℃ and then weighed rendering suspended sediment concentration in mg/l CatNet filtration Filtering in the lab Filtering on board 153 µm 10 µm 63 µm Particle filtration procedure

Results: Mean diameter profile Floc porosity profile Floc density profile

Sea level elevation Julian day (2006)

Sea level elevation Julian day (2006)

Floc model ( Krone, From W. Van Leussen, Estuarine macroflocs and their roles in fine-grained sediment transport. )‏ Volume of interstitial water （ V IS ） ： Avoid in floc (V IS ) Floc volume (V f )

Formula for floc porosity (  ) estimation Bulk volume of floc (V f ) Interstial volume in floc (V IS )

Compare floc porosity data in two cruises Percentage of negative porosity values Year of data collected Grain size µm56 %0 % µm32 %0 % µm6 %0 % Summary of all grain sizes 35 %0 %

Averaged floc porosity profile < 10 µ m µm > 63 µm Average floc porosity µm: % µm: % µm: %

Floc density estimation Deduced density formula Two assumptions:  1. The primary particle density (  p ) was 2.65 g/cm 3  2. The pore water in flocs was sea water (  w =1.025 g/cm 3 )

Average bulk density profile < 10 µ m µm > 63 µm Average Bulk density µm: 1.89 g/cm µm: 1.61 g/cm µm: 1.25 g/cm 3

Bulk floc density µm: 1.89 g/cm µm: 1.61 g/cm µm: 1.25 g/cm 3 Properties of suspended aggregates (Krone, 1978)‏ Density in salt water g/cm Gulfport Channel San Francisco Bay White River (in salt water)‏ Brunswick Harbor Wilmington District Order of Aggregation

Summary Particles in river plume can be identified from its grain size distribution. The results from the 2004 data were not as good as those from 2006 due to the difference of on-board filtration which reduces the chance of breakage of fragile flocs storage and transport. The average calculated floc densities of , , µm were 1.89, 1.61, 1.25 g/cm3, respectively. And the floc porosities were 46.96, 63.95, %, respectively. This approach is different from the traditional floc density estimation derived from settling velocity according to Stokes law.