Grain-size data and Geochemical data of SYW-C core in

Core SYW-C (109°28.59΄E, 18°13.4΄N; 14 m water depth; 1.81 m core length) was obtained from Luhuitou Bay on the east side of Sanya Bay. The core is grayish green and homogenous, with a significant increase in sand at the top 20 cm and 135-181 cm. The shells and their fragments are scattered throughout the core, with a relatively low overall content. The core was split into 181 samples with a 1 cm resolution. The odd numbers of samples were used for coarse fraction weight analysis and grain size analysis, and the even numbers were used for X-ray fluorescence (XRF) analysis and carbonate content analysis.The samples were oven-dried at 60°C, and then each sample (approximately 15 g dry weight) was soaked in distilled water for approximately 24 h to disaggregate, wet-sieved through a 63 µm sieve, and then dried again in an oven. Coarse fraction weights (>63 µm) were then measured, and their percentages were calculated.Approximately 1g of dry sediment from each sample was used for grain size analysis. The organic materials and carbonates were removed with 10% hydrogen peroxide (H2O2) and 10% hydrochloric acid (HCl), respectively, and then the coarse particle fractions (≥ 500 µm) were removed via the wet sieving. After that, the < 500 µm fractions were dispersed with sodium hexametaphosphate ((NaPO3)6), and the grain size analysis was conducted on a Mastersizer-2000 laser particle analyzer. Each sample was measured three times. The relative error was less than 1% for replicate measurements. The grain size analysis was performed at the Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy o Sciences. The relative percentages of sand (≥ 63 µm), silt (4-63 µm) and clay (≤ 4 µm) content were calculated based on the integrated data from both fractions. We extracted sensitive grain size components (0-500 μm) via applying the end-member analysis. End-member analysis is an effective approach for unmixing grain-size data into geologically meaningful end-members through numerical-statistical algorithms (Weltje et al., 1997; Huang et al., 2020). In this study, we performed end-member analysis using parametric methods in the AnalyzeSize software package. The modeling approach employed the Generalized Weibull distribution function for grain-size distribution characterization (Paterson and Heslop, 2015). Based on optimal fitting results, three distinct end-members were identified and selected for further interpretation and discussion.The carbonate content (CaCO3) was determined via a gasometric method. A calibration curve was established by mixing CO2 volumes generated by different Na2CO3 weights with excess 1 mol/L HCl. After that, approximately 0.2 g of dry sediment from each sample was treated with excess 1 mol/L HCl, the CO2 volume was recorded before and after the reaction, and the CO2 volume change was calculated. For every five samples, a correction was applied via a Na2CO3 standard. Replicate analyses of both samples and carbonate standards indicate that the analytical precision was ±1%.Approximately 5 g of ground and sieved samples (<200 mesh) were weighed and pressed into tablets via the boric acid pressing method (Ji et al. 2003) at a pressure of 30 tonnes. Geochemical analysis was performed on an XRF spectrometer (PANalytical Corporation, Netherlands) at the School of Geography, Nanjing Normal University. The instrument uses Hongze Lake sediment GSS-9 (GBW07423) as a standard material for quality control, and the analysis error is less than 5% (Liu et al. 2022).