A comparison of sedimentary aliphatic hydrocarbon distribution between East China Sea and southern Okinawa Trough

Abstract

In this study, 34 surface sediments were collected from the East China Sea (ECS) shelf, and their aliphatic hydrocarbon concentrations measured. The hydrocarbon distribution of the ECS was compared with that of the southern Okinawa Trough (SOT) to explore for possible relations between the two coastal marine areas. Results from principal component analysis performed on hydrocarbon data of ECS and SOT sediments indicated that the first two components explained 74% of the total variance and that the score plot of the two components showed three groups. The first group defined by the 12 SOT sediments contained three sediments on the ECS inner shelf. Eight sediments except one on the ECS inner shelf formed group II, and the remaining 21 sediments located away from the inner shelf (mainly on the mid-to-outer shelf) formed group III. Even though three inner shelf sediments cluster with group I, the separation between groups I and II suggests that the hydrocarbon relation between the inner shelf and the SOT is very weak. Groups II and III do not cluster together; their separation is supported by previous studies showing that Changjiang River sediment tends to remain in the coastal waters and is transported to the south by the coastal currents along the Chinese coast. Also, group I does not cluster with group III, signifying a great difference between them; this can be attributed to little material exchange between the ECS and the SOT because of the Kuroshio Current. In addition, the SOT and ECS inner shelf had carbon preference index values averaging 2.92±0.79 ( n=12) and 4.56±0.93 ( n=8), terrestrial/aquatic ratios averaging 9.64±4.33 ( n=12) and 50.4±58.0 ( n=8), and ( nC 27+ nC 29+ nC 31)/TOC ratios averaging 1731±482×10 −7 g(g C) −1 ( n=12) and 3016±868×10 −7 g(g C) −1 ( n=8), respectively; strongly indicating considerable differences between the two areas. Based on the present results, hydrocarbon export from the ECS inner shelf to the SOT appears to be unlikely.