CHARACTERISTICS OF N-ALKANES IN THE SURFACE SEDIMENTS OF THE EAST CHINA SEA AND THEIR IMPLICATIONS FOR THE DISTRIBUTION OF TERRIGENOUS ORGANIC MATTER

The East China Sea (ECS) is an important sink of organic carbon with complicated and diverse sources, in which there is a huge amount of terrigenous organic carbon coming from the Yangtze River, the Yellow River and the rivers from Taiwan. Therefore, it is indispensable to identify the composition of terrigenous sedimentary organic carbon and trace its fluvial source for carbon flux research. Up to date, the study on the distribution of terrigenous organic carbon in sediments of the ECS is mainly concentrated in some areas such as the estuary areas and the middle and outer shelf regions in a water depth < 120 m, but rare is devoted to the slope of Okinawa Trough (OT) and the outer shelf of the ESC. Little is known about the source-sink process, distribution patterns, sedimentary dynamic mechanisms, and other problems concerning the origin of terrigenous organic carbon. In this paper, we discussed the distribution and transportation of terrigenous organic carbon in the sediment, through the distribution and composition of n-alkanes for 80 surface sediment samples from the ECS outer shelf, slop and trough, together with other indexes such as grain-size, total organic carbon (TOC) and stable carbon isotope δ¹³C. The results show that the terrigenous organic carbon content indicated by δ¹³C and（ΣC₂₇+C₂₉+C₃₁,n-alkane）/TOC vary in a large range in the study area, and from the outer shelf to the trough, they decrease first and increase later. There is a great amount of terrigenous organic carbon deposited on slope and in some special areas of the OT. Dominated by the process of “transportation-deposition-resuspension-transportation” in the slope area, the terrigenous organic matter (TOM) is continuously transported from the interior shelf of ECS to the OT across the outer shelf. The results of CPI suggest that the TOM from ECS inner shelf was mainly sourced from the area of 28.5°—30°N in the Okinawa Trough. To the south of 28.5°N, the TOM in sediments was mainly affected by the materials from Taiwan, while to the north of 30°N, the TOM was mainly derived from the Yellow River and Japan Islands.