Coccolith Mass and Carbonate Flux Data

For each depth interval, a minimum of 200 coccoliths were measured to ensure statistical robustness. Coccolith thickness (Tc) was then calculated from these parameters.                                                      Tc = Gc ×1.5/255                                                    (1)In the above equation, the conversion factor (1.5/255) represents an empirical calibration relating grey-scale intensity (0-255) to coccolith thickness (~0-1.5 µm), based on birefringence measurements under cross-polarized light (Beaufort et al., 2014).

Then, individual coccolith calcite mass was calculated using the equation:                                                      Mc = Ac × Tc × 2.7                                                 (2)where MC is the coccolith mass (in picograms), AC is the coccolith shield area (μm²), TC is the coccolith thickness (µm), and 2.7 pgμm⁻³ is the assumed density of calcite.The flux of coccolith carbonate (Fc) of was calculated as follows:                                           Fc = LSR × sediment dry density × abundance × Mc               (3)where LSR is the linear sedimentation rate obtained from the age-depth model.

As direct dry bulk density measurements were unavailable for core YDY05, an average value of 1.27 g cm⁻³ derived from a nearby BoB core with comparable lithology and depositional conditions was applied. While this assumption may influence absolute flux magnitudes, it does not affect relative downcore trends, which constitute the primary focus of this study. Absolute abundance (A) was used as individual coccolith abundance that calculated from the following equation:                                                                    A = (N×S×V)/(s×v×m)                                    (4)where N is the number of coccoliths counted, S is the total coverslip area (24 × 24 mm²), V is the total suspension volume (10.3 mL), s is the cumulative area of the counted fields of view, v is the volume of suspension dispensed onto the coverslip (300 µL), and m is the dry sediment mass (g).