One way in which to answer the question of the fate of Amazon forests under future climate change is to look to the past. Knowledge of past temperature and precipitation changes and associated vegetation changes will enable us to better predict future changes in vegetation associated with predicted climate changes. Paleoclimate records, such as tree-rings and ice cores, are widely used to reconstruct past climate with the intention of predicting possible future scenarios under climate change. Here, we use lake sediments from the western edge of the Amazon Basin to reconstruct precipitation and associated vegetation changes over the past ~2000 years in order to determine the potential range of future variability under climate change in this region.
In the summer of 2009, we travelled to the Peruvian Amazon to collect lake sediment cores from Lake Limón, and since this time, we have created an age model using 210Pb and 14C dating methods. We have also performed x-ray fluorescence (XRF), lamination, and d13C and d18O analyses on the most recent portion of the sediment. XRF analyses allow us to determine changes in elemental abundance and sediment composition between layers of the core, which may be attributed to precipitation changes in the region. Our results show that the terrigenous elements (Aluminum, Titanium, Iron, Potassium, and Rubidium) are very highly correlated, and a principal components analysis reveals that these elements explain ~40% of the variability seen in the data. In other words, a large portion of the variability seen is from terrestrial input to the lake. A preliminary correlation with climate data reveals that this variability reflects changes in precipitation, but we are currently working on a more thorough analysis to confirm this. We are also working on obtaining grain-size data, which has been shown by others to reflect changes in precipitation and lake level. Colleagues at the Florida Institute of Technology have obtained a record of pollen from this same lake, and thus, we will be able to combine our precipitation record with their pollen record to determine past vegetation changes (if there are any) associated with changes in precipitation. This will then enable us to better predict future precipitation and vegetation changes in this region of the Amazon Basin.
This research is supported by NSF Partnerships for International Research and Education (Amazon-PIRE), with contributions from the Kartchner Caverns scholarship fund.
Project Collaborators: Sarah White, Research and Outreach Scientist, Geosciences, University of Arizona; Jonathan Overpeck, Co-Director, Institute for the Study of Planet Earth, University of Arizona; Scott Saleska, Associate Professor, Ecology and Evolutionary Biology, University of Arizona; Mark Bush, Professor, Biological Sciences, Florida Institute of Technology.