^239+240Pu chrono-marker and migration in sediment cores in China Sea

Radionuclide dating is essential for understanding marine sediment processes, while tracking radionuclide sources and sinks helps assess ocean health and pollution. This study investigated the vertical distribution of ²¹⁰Pb_ex, ¹³⁷Cs and ^239+240Pu in sediment cores from the China Sea. First, we identified three main distribution patterns based on the relative peak activity positions of ¹³⁷Cs and ^239+240Pu, occurring in proportions of 28.6 % (ΔH < 0 cm), 23.8 % (ΔH = 0 cm), and 47.6 % (ΔH > 0 cm), respectively. Second, we evaluated 28 dating combinations using ²¹⁰Pb_ex, ¹³⁷Cs and ^239+240Pu. Notably, we found a strong correlation (R² > 0.95) between depth of ^239+240Pu maximum peak values and sedimentation rates or apparent convection velocities for the first time-indicating that deeper peaks correspond to higher sedimentation rate or apparent convection velocity. Meanwhile, the apparent convection velocity was not greater than the sedimentation rate numerically. Additionally, sedimentation rates showed a relationship with radionuclide inventories (²¹⁰Pb_ex, ¹³⁷Cs, or ^239+240Pu), though this varied regionally (e.g., Southern Okinawa Trough + Bay). By modelling these relationships, we demonstrated that abnormal inventories in specific sediment cores were influenced by local factors, including the Kuroshio Current, river runoff, and geographic setting. These insights provide a critical foundation for future research on natural and artificial radionuclides in marine environments, particularly in ocean dumping zones.