Collaborative Research: Are Amazonian and Andean ecosystems close to a tipping point?

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Amazonian rainforests are famous for the immense biological and cultural diversity they support. These forests are also a vital part of global recycling of freshwater, and their loss has implications for food security for millions of people as well as global climate dynamics. Climate change is threatening these systems and there are concerns that as temperatures rise and rainfall becomes less reliable, these forests might be replaced by low-diversity grasslands. However, it is unclear what level of climate change might trigger a forest-to-grassland transition. Paleoecology can provide information about biological diversity in the past, and how biodiversity patterns changed during past warming events. This research project will investigate two periods of climate warming, one that lasted from about 8000 to 5000 years ago, and another even warmer time that lasted from 128,000 to 120,000 years ago. Ancient lakes build up sediments through time, and by taking a drill-core down through the sediment the history of the region can be captured in the lake mud. The researchers will analyze the fossil and chemical content of lake sediment cores from seven locations in the Amazon and Andes to establish how much the climate changed in the past, and whether those changes were enough to induce a shift from forest to grassland. By looking at a range of locations that vary in moisture, from very wet to quite dry, and degree of warming, the researchers will estimate how close the modern rainforest is to a forest-to-grassland transition. Additionally, new interactions between the collaborating research groups will include a co-taught paleoecology/paleoclimatology course, a sponsored category in a local film festival, and training of at least 10 undergraduates, two doctoral students, and one postdoctoral researcher. The research will address a number of hypotheses relating to climate-vegetation responses such as flickering, teleconnections, ecosystem buffering, and tipping points. By using organic geochemical data to estimate paleotemperature, leaf wax isotopes to estimate precipitation, sediment chemistry to characterize droughts, fossil pollen to reconstruct vegetation, and charcoal to reconstruct fire frequency, the researchers will investigate ecosystem change under conditions as much as 2 degrees C (4 degrees F) warmer than the present. The Last Interglacial will provide an index of scale of change in traits, fire prevalence and community composition in a climate 1-2 degrees C warmer than modern. In the directly-dated Holocene, the data will assess sub-decadal variance in ecosystem indicators, and allow rates of change to be investigated. Currently, no high-resolution records of Amazonian temperature exist, so the novel approach of separating climatic change from that of ecological proxies will be transformational for quantitative neotropical paleoecology.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.