Coccoliths are widely present in marine sediments of the South China Sea and closely associated with paleoenvironmental changes. This study investigates the morphological variations and driving factors of coccoliths since the Last Glacial Maximum(LGM) by analyzing the morphology and related indicators of Noelaerhabdaceae coccoliths in sediment samples from core MD18-3569 (0.01~12.41 m; 0.69~26.58 ka) in the northeastern South China Sea(22°09.30’N, 119°49.24’E at water depth 1320 m), and a total of 155 samples were collected, with a sampling resolution of approximately 167 years. Morphological attributes such as coccolith length, thickness, area, and mass were obtained through microscopic measurements and computational formulas. Coccolith morphological constants were used to evaluate preservation conditions. Based on these data, morphological divergence index and calcification index were calculated. Using the PyCO2SYS model, ocean carbonate system parameters were reconstructed to explore their impact on coccolith morphology.
The results show that coccolith length ranged from 2.69 μm to 3.86 μm(mean: 3.20 μm) since the LGM, with significant variability but no clear trend. Thickness ranged from 0.07 μm to 0.17 μm(mean: 0.13 μm) and exhibited a decreasing trend since the LGM. Coccolith mass varied between 2.31 pg and 9.02 pg(mean: 5.61 pg), also showing a decreasing trend since the LGM. Coccolith morphological constants indicate good preservation and high data reliability. Morphological divergence index results suggest a decline in coccolith size diversity, reflecting reduced seasonal variation and regional productivity. Calcification intensity metrics indicate a weakening of calcification since the LGM.
By comparing temperature, salinity, and ocean carbonate system parameters, the study identifies rising atmospheric CO2 concentrations and resultant ocean acidification as the primary factors contributing to reduced coccolith calcification. The impacts of temperature and salinity were relatively minor. These findings demonstrate the complex response of Noelaerhabdaceae coccoliths to environmental changes and highlight the significant roles of regional climate variations and carbonate system evolution in shaping coccolith morphology.
Gao J., Zhou X. & Liu C., 2025. Variations of coccolith morphology and their influencing factors in the northeastern South China Sea since the last glacial maximum. Quaternary Sciences 45(2): 516-525. Article.
