This study belongs to one part of FATES research program, which studies the fate of terrestrial substances in Kaoping river-sea system. The task is to study the components and properties of sediments and spatial distribution of sedimentation rates off the southwest Taiwan by analyzing water content, TOC, CaCO3, grain size, P-wave velocity and radionuclides 210Pb and 137Cs in sediments.
Thirty cores collected for this study were divided into three groups based on topography and they are Kaoping continental shelf, slope and canyon. The highest TOC content is 1.53 % in ORI732-ST31 and TOC content ranges from 0.20~0.93 % for the rest of sediments from other stations. The highest CaCO3 content is found in ORI732-ST18, 30, ORI779-ST1, and ST12. Most of the CaCO3 content is greater than 4% at these four stations. Probably because of the lower sedimentation rates that result in less terrestrial substances for diluting the CaCO3. In the shelf and slope regions, the distribution of grain size progressively decreases as the water depth increases. Grain size in the stations farther down the canyon, however, is coarser than those at upper canyon. It suggests that there is other sediment source for stations in the canyon in addition to the Kaoping river.
The sedimentation rates derived from 210Pbex profiles range from 0.073~0.168 cm/yr in shelf, 0.033~0.670 and 0.094~0.411 cm/yr in continental slope and canyon, respectively. Sedimentation rates are all less than 0.2 cm/yr in the shelf area, but there are five stations with sedimentation rates higher than 0.2 cm/yr in the slope and canyon areas. Among the five stations, the sedimentation rate is up to 0.670 cm/yr (ORI779-ST9), suggesting that 302~822 m deep in the slope and 975~1156 m deep in the canyon are the deposition centers.
In some stations, anomalously low 210Pbex activities exist in surface or sub-surface sediments, indicating that the low 210Pbex activity sediments may be typhoon-induced turbidite sediments. According to Central Weather Bureau’s typhoon catalog, in the year of coring there were seven typhoons striking Taiwan. Among these typhoons, Hai-tang was the strongest one, suggesting that the turbidite sediments mentioned above were likely caused by typhoon Hai-tang. Besides, turbidite sediments appear at water depth of over 700 m, indicating episodic turbidite events are an important way to transport particles offshore.