A comprehensive stalagmite investigation distinguishing anthropogenic and natural signals in Madagascar between 1680 and 1860

Abstract

Abstract Disentangling anthropogenic from natural induced changes is difficult, but crucial to accurately assess the specific environmental impacts of humans’ actions versus climate in the paleoclimate records. Here we combine a new set of proxies, including stable isotopes, element concentrations (mainly Mg, Sr, and U), and detailed mineralogy to better distinguish the impacts of these two factors in the stalagmite records. We studied the period between 1680 and 1860 CE because of the known historical events in Madagascar history (e.g., western colonization and the growth of Malagasy kingdom). This is an ideal period to study given these known events. Our data suggest that redox conditions during alternating wet and dry conditions is revealed by U/Ca covarying with δ18O, but extreme climatic conditions may reverse that relationship. We also found an Mg/Ca increase combined with a decrease in δ13C starting ca. 1820 CE that suggest anthropogenic imprints associated with local burning in Madagascar. This new multiproxy combination, paired with a thorough understanding of Madagascar history over this time allowed us to distinguish anthropogenic versus natural–induced signals in Madagascar stalagmite. This unique and novel pairing of proxies can be used to understand and predict human and natural induced changes in similar settings.