Long-term changes in precipitation recorded by magnetic minerals in speleothems

Speleothems are important paleoclimate archives. Researchers typically compile measurements of stable isotopic ratios dated using high precision U-Th radiometric techniques to reconstruct regional and global climate. Magnetic material incorporated within speleothems can provide an independent means of connecting large-scale climatic changes with their impact on more localized processes in soils overlying cave systems. Under certain environmental conditions, pedogenic processes can produce magnetite nanoparticles. Enhancement of pedogenic magnetite in soil profiles depends strongly on local precipitation. Pedogenic magnetite can be subsequently transferred via drip-waters into underlying cave-systems and incorporated into speleothems as they grow. Here, we employ high-resolution magnetic methods to analyze a well-dated stalagmite from Buckeye Creek Cave, West Virginia (USA), and find that changes in magnetite concentration follow both changes in stable isotopes measured in the same stalagmite and global climate proxies. We interpret the changes in magnetite concentration as reflecting variations in local pedogenic processes, controlled by changes in regional precipitation. This record demonstrates how magnetic measurements on speleothems can constrain interpretations of speleothem climate proxies.