Paleohydrological variations revealed from the TMZ05 Borehole in the Qiantao Basin of the Yellow River

Paleohydrology serves as a critical historical reference for studying and assessing flood risks in river basins. We analyzed a ～19 m deep borehole core (TMZ05) from Tumote Right Banner in the Qiantao Basin of the Yellow River and reconstructed the paleohydrological evolution over the past 19 ka using sediment grain size and geochemical proxies, including the grain-size U value (U=p(16～80 μm) / p(2～16 μm), flood energy index (FEI=(pEM4+pEM5)/(pEM3+pEM4+pEM5)) from grain size end-member components, and ln(Zr/Rb) values. Optically stimulated luminescence (OSL) and accelerator mass spectrometry (AMS) ¹⁴C dating were applied to establish the chronological framework. Results reveal that since the Last Glacial Maximum (LGM), the frequency and magnitude of paleohydrological events in the region have been generally decreased but exhibited distinct phases. Periods of 18.5～14 ka and 8.5～6 ka were characterized by low-frequency and low-amplitude fluctuations, while 14～8.5 ka showed intense high-frequency and high-amplitude hydrological variability. After 6 ka, both the intensity and variability of paleohydrology were gradually increased. Furthermore, five high-frequency and high-amplitude paleohydrological phases: 19～16.5 ka, 14～11.7 ka, 11～9.7 ka, 9.4～8.5 ka, and 4.2～1.6 ka indicated by high-resolution proxies (FEI and ln(Zr/Rb)), during which catastrophic flood events occurred frequently in the Yellow River Basin. Regional paleoenvironmental comparisons indicate that these high-frequency and high-amplitude hydrological phases corresponded to intensified flood disasters, and occurred mainly during the transitional periods of climate system, implying that the instability in hydroclimatic regime could seriously disrupt the equilibrium of fluvial morphology.