The Utilization of Shell Oxygen Isotope Analysis to Reconstruct Past El Nino Patterns

Board Of Regents, Nshe, Obo University Of Nevada, Reno, Reno NV

Investigators

Abstract

Dr. Christopher Jazwa of the University of Nevada, Reno (UNR) will conduct a research project to investigate patterns of past El Niño events and their effects on human settlement and subsistence. The project will use data from archaeological faunal collections to trace El Niño frequency within a broader context of environmental variations, with implications for human responses to present-day environment change. In general, there is an expectation that periods with more frequent El Niños will have negative effects on marine food resources, including stocks of economically important fish and shellfish species. In the past, this could have prompted changes in human subsistence patterns and social structures. Today, it could affect economic systems reliant on marine foods. Archaeological sites and materials are uniquely positioned to model these systems and this project will take advantage of faunal materials from well-dated archaeological contexts from coastal California. Furthermore, this project is designed to refine methodologies for assigning archaeological sites to different seasons of occupation, which may shift in response to environmental change. Funding from this project will assist in the development of the new Human Paleoecology and Archaeometry Laboratory at UNR. This work will closely involve graduate and undergraduate students during all stages of data collection, providing training in field and laboratory analyses. Environmental and archaeological research within Channel Islands National Park will assist with the park's missions of preservation and inventorying their valuable cultural resources. Members of the local Chumash tribe will be involved in archaeological fieldwork for this project. This project will use stable oxygen isotopic analysis of California mussel (Mytilus californianus) shells from archaeological sites to reconstruct patterns in local sea surface temperature at the time that bands of shell carbonate were deposited on the shell. This will allow the PI to address three primary questions: (1) How has the frequency of El Niño events varied over the course of the last 8,000 years? (2) What are the effects of these changes on human settlement and subsistence patterns in coastal ecosystems? And (3) with what accuracy can season of occupation of archaeological sites be assigned with different isotopic sampling techniques for California mussels. The PI has been collecting modern mussel shells from a test location on southern Santa Rosa Island, California, part of Channel Islands National Park, at three-month increments from 2015-2017. This included the 2015-2016 El Niño winter. With the assistance of graduate and undergraduate students, the modern shells will be sampled and analyzed for stable oxygen isotopes to refine methodologies for observing El Niño and assigning shells to season of harvest. Excavation of shell-rich archaeological sites during a summer season, along with existing collections, will provide samples to reconstruct past environmental patterns and human responses. Although El Niño events have global effects, anomalies in sea surface temperature are especially strong along the west coast of the Americas, making California an ideal location to address these questions. Therefore, observed patterns of past El Niño frequency can be applied to understand human responses to climate change around the world.