Suspended particle property variations in Gaoping Submarine Canyon

Ray T. Hsu and James T. LiuInstitute of Marine Geology and Chemistry, National Sun Yat-sen University, Kaohsiung, Taiwan, R.O.C.

Gaoping river-sea systemGaoping river-sea system

Estuarine system:River plumeBiogenic productionFlocculation & deflocculation

Canyon Channel:LandslidesDebris flowsTurbidity currentNepheloid layers

Shelf Region:Biogenic productionResuspension

Particle settlingParticle settling

Internal tide

Shelf margin

C. Benthic nepheloid layerC. Benthic nepheloid layer

A. Hypopycnal plumeA. Hypopycnal plumeB. Hyperpycnal plum

e

B. Hyperpycnal plume

Diversities of suspended particles in Diversities of suspended particles in coastal watercoastal waterDiversities of suspended particles in Diversities of suspended particles in coastal watercoastal water> 500 μm

> 63 μm

> 250 μm

> 10 μm

Optical microscopyOptical microscopyOptical microscopyOptical microscopy

Study areaStudy area

Gaoping RiverGaoping River

8/27-28/2006

Gaoping Gaoping Submarine Submarine CanyonCanyon

Taiwan StraitTaiwan Strait

6/18/2004

Investigation schemeInvestigation schemeDate 6/18/2004 8/27-28/2006

Water Sampling

Sampling Periods 8 Hours 24 Hours

Sampling intervals 1 Hour About 3 hours

Sampling volume

10 L at 6 different depths

60 L (at 20 m and 15 m above bed)

Number of profiling 16 8

CTD and LISST-100 profiling

Sampling intervals 1 Hour About 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 cruise 2006/8/27-28 cruise

All filtered particles were dried in the oven at 50 All filtered particles were dried in the oven at 50 ℃℃ a and then weighed rendering suspended sediment concennd then weighed rendering suspended sediment concentration in mg/ltration in mg/l

CatNet filtrationCatNet filtration

Filtering in the lab

Filtering on board

153 µm

10 µm

63 µm

Particle filtration Particle filtration procedureprocedure

Results:Results:

Mean diameter profile Floc porosity profile Floc density profile

Sea level elevation

Julian day (2006)

Sea level elevation

Julian day (2006)

Floc modelFloc model

( Krone, 1986. From W. Van Leussen, 1989. Estuarine macroflocs and their roles in fine-grained sediment transport. )

quartz) (as g/cm 2.65=density paritcleprimary asume :

eunit volum :

processweight -dry-fillteringby

determinedion concentratsediment suspended :

LISSTby measuredion concentrat volume:

/*

*

3p

i

pip

if

V

SSC

VC

VSSCV

VVCV

Volume of interstitial water（ VIS）：

VIS V f Vp

VC Vi SSC Vi /p

Avoid in floc (VIS)

Floc volume (Vf)

Formula for floc porosity (Formula for floc porosity () ) estimationestimation

VIS V f

V f Vp V f

VC Vi SSC Vi /p

VC Vi

1 1p

SSCVC

quartz) (as g/cm 2.65=density paritcleprimary asume :

eunit volum :

processweight -dry-fillteringby

determinedion concentratsediment suspended :

LISSTby measuredion concentrat volume:

/* *

3p

i

pipif

V

SSC

VC

VSSCVVVCV

Bulk volume of floc (Vf)

Interstial volume in floc (VIS)

Compare floc porosity data in Compare floc porosity data in two cruisestwo cruises

Percentage of negative porosity values

Year of data collected

2004 2006

Grain size

0.45-10 µm 56 % 0 %

10-63 µm 32 % 0 %

63-250 µm 6 % 0 %

Summary of all grain sizes

35 % 0 %

Averaged floc porosity profileAveraged floc porosity profile

< 10 µm

10-63 µm

> 63 µm

Average floc porosityAverage floc porosity• 0.4-10 µm:

46.96 %• 10-63 µm:

63.95 %• 63-250 µm:

85.87 %

Floc density estimation

Deduced density formula

Two assumptions: 1. The primary particle density (p) was 2.65 g/cm3

2. The pore water in flocs was sea water (w=1.025 g/cm3)

f M p Msw

V f

M p

V f

Vswsw

V f

SSCVi

VC Vi

VC SSC p Visw

VCVi

SSC

VC

VC SSC p sw

VC

SSC

VC sw

sw

p

SSC

VC

sw 1

sw

p

SSC

VC

Average bulk density Average bulk density profileprofile

< 10 µm

10-63 µm

> 63 µm

Average Bulk density• 0.4-10 µm:

1.89 g/cm3

• 10-63 µm:

1.61 g/cm3

• 63-250 µm:

1.25 g/cm3

Bulk floc densityBulk floc density 0.4-10 µm: 1.89 g/cm3

10-63 µm: 1.61 g/cm3

63-250 µm: 1.25 g/cm3

Properties of suspended aggregates (Krone, 1978)Density in salt water 1.025 g/cm3

1.2051.1061.0781.065

Gulfport Channel

1.2691.1791.1371.1131.0981.087 1.079

San Francisco Bay

1.2121.1091.0791.065

White River

(in salt water)

1.1641.0901.0671.056

1.2501.1321.0931.074

01 23456

Brunswick Harbor

Wilmington District

Order of Aggregation

SummarySummary Particles in river plume can be identified from its gr

ain 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 0.4-10, 10-63, 63-250 µm were 1.89, 1.61, 1.25 g/cm3, respectively. And the floc porosities were 46.96, 63.95, 85.87 %, respectively.

This approach is different from the traditional floc density estimation derived from settling velocity according to Stokes law.