Cave Dripwater Magnetic Minerals Record Seasonal Rainfall Variability: New Insights From a 5-Years Field Monitoring in Central China

Abstract

Stalagmites provide an invaluable archive at high-resolution for paleoclimate studies. However, it is challenging to extract independent hydroclimate signals from stalagmites due to the scarcity of reliable hydrological proxies. Although the magnetic parameters of stalagmites have shown great potential in recording regional hydrological signals, the mechanistic linkages between magnetic minerals and hydroclimate variability remain unresolved, limiting the broader application of stalagmite magnetism. This study addresses this knowledge gap through a 5-year monitoring campaign targeting Heshang (HSD), Haozhu (HZD), and Chang (CD) caves in central China. We systematically analyzed the magnetic minerals in coupled soil-bedrock-dripwater-stalagmite systems using integrated environmental magnetic techniques. The results demonstrate that magnetic minerals in the dripwater are dominated by magnetite/maghemite (detrital origin from overlying soils) and goethite (mixed sources including pedogenic, bedrock derived, and authigenic contributions, but not specifically). Seasonal analysis reveals that magnetite/maghemite flux (M_Mag/Mgh-flux) in the HSD dripwater exhibits pronounced wet-season (May to September) enhancement, which is closely correlated with the rainfall-driven soil flushing. This pattern attenuates in the HZD and CD systems due to their reduced soil-bedrock cover thickness. In contrast, the relative concentration of goethite (R_Gt) displays a consistent sensitivity to regional rainfall across all the monitored caves, especially HSD, suggesting its broader utility as a hydroclimate proxy. Our findings establish a mechanistic framework linking stalagmite magnetic mineralogy to rainfall dynamics, identifying M_Mag/Mgh-flux and R_Gt as robust dual proxies for reconstructing past hydrological variability in karst systems.