Source identification and co-occurrence patterns of major elements in South China Sea sediments

Abstract

South China Sea (SCS) sediments have multiple sources. The quantitative assessment of the potential sources is crucial to understanding the source-to-sink transport processes in the SCS. In this study, 1987 surface sediments were collected from the entire SCS (excluding the Gulf of Thailand). Major elements were measured, and the co-occurrence relationships among the major elements and grain sizes were investigated by utilizing network analysis. Positive matrix factorization (PMF) was used for the identification of potential sources and the quantitative assessment of their relative contributions. Only nine elements (SiO2, Al2O3, Fe2O3, CaO, MgO, K2O, Na2O, TiO2, and loss on ignition (LOI)) were chosen for the PMF analysis. The calculated signal-to-noise ratios of MnO and P2O5 were extremely low, making these two elements unsuitable for analysis. Four potential sources were identified from the combined PMF factor profiles and factor contributions, representing a northern and western terrigenous source, a southeastern terrigenous source, a biogenic carbonate source, and a source of sandy sediment on the shelf. The PMF factor profiles correspond to the four communities detected based on the co-occurrence relationships. These results support the validity of the four-factor PMF model. In addition, the spatial trends of the relative contributions of terrigenous elements (TiO2, Fe2O3, Al2O3, K2O, and MgO) are comparable to the pattern of the oceanic currents in the SCS. Therefore, the transport of the terrigenous elements in the SCS is controlled by hydrodynamic conditions.