Indication of lipid biomarkers in sediment records for the Qiongdong Upwelling intensity and preliminary study of it's controlling factors

The n-alkanes and fatty acids were analyzed in two sediment cores at the upwelling edge region (Station S5) and center area (Station S10) of eastern Hainan Island, the source and degradation characteristics of organic matter were comprehensively analyzed by combining organic carbon content, particle size, carbon stable isotope (δ¹³C) and other parameters. The interannual variation of upwelling intensity in the study area was reconstructed using the diatom abundance parameter ∑16 : ∑18 of fatty acids. The grain size results show that Station S10 is located near the center of upwelling, with coarse grain size and mainly sand; Station S5 is located at the edge of upwelling, with fine grain size and mainly silt. The δ¹³ C and fatty acids parameter (∑C_20-:0/∑C_20+:0) of the two stations show that both stations are dominated by marine source input. The degradation degree of organic matter in Station S10 is greater than that in Station S5. The diatom abundance parameters of fatty acids and the percentage of phytoplankton fatty acid indicate the primary productivity of Station S10 is higher than Station S5, and ∑C₁₆ : ∑C₁₈ is used to indicate the interannual variation of the intensities of the upwelling in the study area; the upwelling intensity shows weak, strong, and weak signals between 1925−1950, 1950−1980, and 1980−2008. It is consistent with the interdecadal trend of Pacific Decadal Oscillation. El Niño-Southern Oscillation may regulate the upwelling intensity in a short time scale, while in a long time scale, it may be mainly regulated by Pacific Decadal Oscillation.