Where have all the sediments gone? The fate of sediments in the Taiwan Strait: A reassesment Chih-Chieh Su, Man-Shan Chang, Horn-Ru Liao, Ho-Shing Yu Institute of Oceanography, NTU 20, Feb, 2008 Chih-Chieh Su, Man-Shan Chang, Horn-Ru Liao, Ho-Shing Yu Institute of Oceanography, NTU 20, Feb, 2008

Outline Previous study –Relict sediments? Short-term changes Chronology of sediment cores Where have all the sediments gone? –What we know… –What we “don’t” know…

Changyun Ridge Wuchu Depression Kuanyin Depression Taiwan Banks Penghu Channel

Emery (1952; 1961) In general, any shelf sediment belongs to one or more of five main groups: Authigenic (glauconite and phosphorite) Organic (Foraminifera and shells) Residual (weathered from underlying rocks) Relict (remnant from a different earlier environment － such as a now-submerged beach or dune) Detrital (presently supplied chiefly from adjacent river mouths, beaches, or sea cliffs)

Emery ( 1968 )

Boggs ( 1975; 1979 ) continued using Emery’s concept of relict sediments mud belt along the coast of mainland China → modern sediments sandy sediments in Taiwan Strait –in the nearshore area of Taiwan → Holocene to modern sand –central part of Taiwan Strait → relict sediments from mainland China A large area of the Strait surrounding the Penghu Island was covered by palimpsest sediment formed by mixing of modern and relict sediment.

Boggs et al. ( 1979 )

Chiu ( 2000 ) Modern muddy sediment Relict sediment Palimpsest sediment Modern sandy sediment

Chang ( 2002 ) Modern muddy sediment Relict sediment Palimpsest sediment Modern sandy sediment

Liu et al., 1998

Liao ( 2005 ); Liao et al. (2008)

Outline Previous study –Relict sediments? Short-term changes Chronology of sediment cores Where have all the sediments gone? –What we know… –What we “don’t” know…

Location map of the surface sediment

median sorting

Milliman et al., 2007

Outline Previous study –Relict sediments? Short-term changes Chronology of sediment cores Where have all the sediments gone? –What we know… –What we “don’t” know…

Location Map ( ) ( ) ( )

1.00 cm/a 0.12 cm/a 1.46 cm/a 0.18 cm/a 1.06 cm/a 1.25 cm/a 0.21 cm/a 1.08 cm/a 0.18 cm/a 0.05 cm/a 0.70 cm/a

OR542 BC9 (1999/3/9)

Outline Previous study –Relict sediments? Short-term changes Chronology of sediment cores Where have all the sediments gone? –What we know… –What we “don’t” know…

What we know… The sediments in the Taiwan Strait are not the so called “relict sediments”, they are the products of the action of modern tidal currents. Taiwan is the major source of modern sediments in the Taiwan Strait.

Liao, 2005

What we don’t know… Where did the “old” sediments in the Taiwan Strait (Chanyun Ridge) come from? –mainland China? –Taiwan? –Penghu Channel?

2008 Joint Hydrographic Survey Grain Size Analysis Clay Mineral Composition Trace Element Distribution Thermoluminescence Dating (TLD)

It’s not complicated, but “VERY” dynamic!