Nickel Isotopes Reveal Enhanced Continental Chemical Weathering During Paleocene–eocene Hyperthermals: Evidence from Coal-Bearing Deposits of the Fushun Basin

The Paleocene–Eocene interval (~59–50 Ma) was characterized by frequent hyperthermal events associated with rapid global warming and intensified hydrological cycling. Understanding how continental weathering responded to such climate perturbations is critical for evaluating climate–weathering feedbacks. However, whether the increased terrestrial material input observed during hyperthermals reflects enhanced erosion alone or also involves intensified chemical weathering remains debated due to limited direct geochemical constraints.Terrestrial basin sediments record variations in catchment-derived weathering products and therefore provide important archives for investigating continental weathering during extreme climate events. Here we investigate lacustrine–swamp coal-bearing deposits from the Fushun Basin in northeastern China to trace changes in catchment weathering and riverine solute input during Paleocene–Eocene hyperthermals. Nickel isotopic compositions (δ⁶⁰Ni) and Ni/Ti ratios were analyzed to constrain variations in terrestrial Ni input. The results show pronounced increases in Ni/Ti ratios accompanied by heavier δ⁶⁰Ni values within hyperthermal intervals. Elevated Ni/Ti ratios indicate enhanced Ni enrichment relative to detrital input, while heavier δ⁶⁰Ni values may reflect an increased contribution of dissolved riverine Ni. Together, these signals indicate enhanced input of isotopically heavy dissolved Ni during hyperthermals, suggesting that the increased terrestrial input reflects not only intensified catchment material transport (erosion) but also strengthened continental chemical weathering under a warmer and wetter climate. These findings provide new geochemical evidence for enhanced continental weathering during hyperthermal warming and demonstrate the potential of Ni isotopes combined with elemental ratios for tracing terrestrial dissolved inputs during past climate perturbations.