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Can trace element ratios in Olivella biplicata shells from California be used to reconstruct paleoclimate?
Seasonality is a fundamental aspect of climate at mid-to-high latitudes but finding records of past climate with seasonal-resolution is difficult outside of the tropics. This limits our understanding of the role of seasonality in controlling mean climate and our ability to model this aspect of climate. Recently marine mollusk shells have shown great potential to act as archives of seasonal-resolution climate. By analyzing the stable isotope and trace element composition of successive samples along the cross-section of a shell then the history of seawater temperatures and salinity experienced by the mollusk over its lifetime can be reconstructed.
Olivella biplicata shells are very commonly found (likely over 1 million in total) in archaeological sites around the western US as they were used as a form of currency. The oxygen isotope composition of these shells has been shown to faithfully record the seasonal sea surface temperature (SST) range (Eerkens et al 2005, 2007, 2010). However there have been no high-resolution studies to investigate whether trace element ratios such as Mg/Ca or Sr/Ca within the shells also record environmental information or are more strongly influenced by biological factors such as growth rates. This project aims to investigate the relationships between instrumental oceanographic records, such as seawater temperature and salinity, and the trace element profiles of modern Olivella biplicata shells. If clear relationships can be determined then this would be a great step forward in developing archaeological marine mollusk shells as archives of paleoclimate information in California and further north. The data generated by this study may also be of assistance to archaeologists investigating former trade routes of American Indian communities in the region.
The project will involve micromilling of modern and archaeological marine mollusk shells and stable isotope and trace element analysis. Students would gain experience in micromilling, microbalances, and stable isotope and trace element mass spectrometry.
Project Time Allocation: Sample Prep./Microscope Lab = 50%, Chemistry Lab = 50%