New Perspectives on Paleo-ENSO Conditions in Coastal Peru as Seen Through Short-Lived Bivalves

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El Niño and La Niña events, collectively called El Niño-Southern Oscillation (ENSO), are the largest source of year-to-year climatic and environmental variability that affects people around the world. For example, El Niños cause droughts in Australia and Southeast Asia while producing damaging floods along the west coast of the United States, Ecuador and Peru. La Niñas produce the opposite effects and both can have significant economic and natural hazard impacts. Recent studies have identified more than one type of ENSO event in the instrumental record, called Central Pacific, Eastern Pacific, or Coastal El Niño events based on the region with greatest rainfall. These different types of El Niños may explain why ENSO reconstructions from the western, central, and eastern Pacific do not always agree. Furthermore, questions remain whether or not this diversity of ENSO events occurred before the 20th century when temperatures were cooler, or occurred during prior warm periods. This project seeks to fill a gap in our knowledge of past ENSO behavior by providing a new record of ENSO variability in north-central Peru for the period 2800 to 2100 years ago, a critical area and time frame currently lacking records of ENSO variability. Our understanding of past and present ENSO is important for refining global climate models used to forecast future climate conditions and in planning for short and long-term impacts from changing climate.This project leverages the expertise of paleoclimatologists and archaeologists while training students in a multidisciplinary approach that will develop a new reconstruction method that could be used in other locations with abundant shell material. The final product will be a new record of ENSO variability in north-central Peru spanning 2800 to 2100 years before present. The study sites are three Early Horizon (800 to 100 BCE) archaeological sites (Caylán, Huambacho, and Samanco), all part of an early urban society in the coastal Nepeña Valley, Peru. The project uses shells from two short-lived bivalve species (Donax obesulus and Mesodesma donacium) excavated from several archaeological units within these three sites. These two species have different but complementary habitat preferences (warm vs. cold) that make them useful to capture El Niño and La Niña events; however, both species are short-lived (1 to 3 years). Instead of building a continuous record of individual ENSO events, this project will reconstruct seasonal temperature and salinity variability from modern and archaeological specimens for individual time slices from intra-shell oxygen isotope measurements, similar to the single foraminifer approach used in marine sediment cores. The integration of archaeological data will provide a crucial perspective on the resilience or vulnerability of coastal societies to ENSO variability on long time periods. The project will support two relatively early career faculty (one female), a graduate student, and one or more undergraduates who will work in the PIs' PAST laboratory (Paleoclimate and Anthropology Studies), which brings natural and social scientists together to foster interdisciplinary collaboration.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.