Sedimentary Flux Study on the Ilan Shelf and the Southern Okinawa Trough

• Main Authors: Yu-Fu Lai, 賴昱甫
• Other Authors: 林曉武
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/26025502893527561695

碩士 === 國立臺灣大學 === 海洋研究所 === 103 === LangYang River exports 5~17 million tons of suspended materials per year to the Ilan Shelf and later to the southwestern end of the Okinawa Trough. It is the most important suspended materials source of the South Okinawa Trough (SOT). However, mass balance disputes exist between the the source (the LangYang River) and fate of particle deposited in the SOT. This thesis investigates sedimentation rates and sediments properties in order to resolve the unbalance problem. Sediment samples were taken from the Ilan Shelf, Ilan Ridge, and Southern Okinawa Trough and determine the following parameters, grain size, density, porosity, magnetic susceptibility and sedimentation rates. The results show that Langyang River is indeed the major source of sediments in the region, from both physical properties and sediment budget. Sediment density decreased from shelf eastward to the Okinawa Trough. Magnetic susceptibility values vary irregularly due to inputs from volcanic and hydrothermal fluid of the Turtle Island. Coarse-grained sediments were found at the Ilan Ridge, and also on the Ilan Shelf with sand content reaching more than 50%. Grain size decreased rapidly away from the shelf with fine-grained clay became the predominant type of grain in the SOT. Sedimentation rates on the Ilan Shelf are high (>0.6cm/yr) and decrease northward and southward with increasing water depth away from the River mouth. However, another depocenter was found away from shelf at water depth about 1000 ~ 1500 m where higher sedimentation rate could reach >1 cm/yr. Based on sedimentation rate, the total sediment buried in this study region could reach 7.17 Mt per year. This value is very similar to that of the river particle annual export value of 6 Mt/year by Kao and Milliman (2005).