Tree rings go with the flow of the Amazon

University of Leeds-led research has used tree rings from eight cedar trees in Bolivia to unlock a 100-year history of rainfall across the Amazon basin, that contains the world's largest river system. The new study shows that the rings in lowland tropical cedar trees provide a natural archive of data closely related to historic rainfall. Researchers measured the amounts of two different oxygen isotopes trapped in the wood’s rings: oxygen-16 and the heavier oxygen-18. By looking at the varying amounts of the two isotopes, they could see how the pattern of rainfall changed year by year. This allowed them to see how much it rained over the Amazon basin over the past century. The lead author of the study, Roel Brienen from the School of Geography at the University of Leeds, said: “We already knew that some tropical tree species form annual rings and we also anticipated that the isotopic signature in these rings might record changes in the climate. “What surprised us, however, is that just eight trees from one single site actually tell us how much it rained not just at that site but over the entire Amazon catchment.