Distribution pattern and controlling factors of redox sensitive elements in the surface sediments from four typical transects in the South China Sea

Redox sensitive elements play an increasingly important role in environmental analysis. However, few studies have been devoted so far to the distribution pattern of the redox sensitive elements in the seafloor surface sediments. In this paper, seventy-five surface sediment samples were collected and analyzed from the four representative transects in the South China Sea along 18°N, 10°N, 6°N, and 113°E respectively. The contents of main elements and trace elements (including Mo, V, and U) are measured in addition to grain sizes of sediments and enrichment factors of redox sensitive elements. The distribution pattern and controlling factors of redox sensitive elements are then discussed in the paper. Results show that the variations in V and U contents in each transect are in fact very similar. The content variation of Mo is similar to the overall trends of V and U, but more intense than V and U changes. Obviously, the average content of Mo is enriched while V and U depleted in the transects except slightly enriched V in the transect Ⅰ. The contents of V and U in all transects are mainly controlled by the contents of terrigenous debris and biological carbonate as well as the adsorption of fine-grained sediments, whereas the influence of redox environment is low. In contrast, the distribution of Mo mainly depends on the seabed redox environment, but not the contribution of terrigenous debris content and the adsorption of fine-grained sediments. The lower content and enrichment factor of Mo in the Southwestern Sub-basin of the South China Sea may probably attribute to oxidized environment caused by the underflow activity.