RAPID: El Nino Isotopic Signature

In this study, investigators seek insight into human responses to climate change in marine environments. In particular, they wish to understand patterns of El Niño intensity and frequency in the past, and how this influenced past human populations. As archaeologists, the investigators are well-suited to understand complex long-term human-environmental dynamics using climatological records and the material record from archaeological sites. El Niños influence human populations through changes in weather, often in the form of heavier rains and larger storms along the southwest coast of the United States, and an increase in sea surface temperature (SST). This change in SST is particularly relevant because it is accompanied by decreases in marine productivity, which often leads to large scale death of marine life along the west coast of the United States and South America. This severely affected the diet of past coastal populations who derived a large proportion of their food from the ocean. Today, El Niños can cause a collapse of fishing industries. This study will refine methods for using elements of the archaeological record to reconstruct El Niños and long-term patterns of SST in the past.

A team of researchers led by Dr. Christopher Jazwa will take advantage of the current extreme El Niño and collect SST data and California mussel (Mytilus californianus) shells that contain a record of elevated water temperature. The oxygen isotope in the calcium carbonate that makes up the outer layers of California mussel shells is influenced by SST at the time it is deposited. This layer is deposited in bands over the lifetime of the mussel, so it is possible to use this signature to reconstruct patterns in SST through time. In this project, investigators will be traveling to Santa Rosa Island, CA, to collect SST data and living mussels in January, March, May, August, and November of 2016. By collecting samples and data during the El Niño and the summer/fall immediately afterward, it should be possible to obtain a signature of elevated SST in the isotopic signature of the shells. Because El Niños are difficult to predict in advance, it is essential that the researchers travel to the field quickly once the appropriate signature has been confirmed. The sampling location is adjacent to archaeological sites with evidence for at least 7500 years of human occupation. These sites include abundant evidence of fishing and shellfishing, including mussel shells. The methods developed in this study can be directly applied to mussels from archaeological collections for three purposes: 1) track past patterns in El Niño cycles; 2) determine long-term patterns in SST; and 3) assign individual shells to particular seasons during the year to understand seasonal movement of past human populations. Fieldwork and laboratory sample processing will be done with the assistance of undergraduate and graduate students, aiding in their education and development as archaeologists. Finally, research will be done in part to satisfy the goals of Channel Islands National Park to inventory the valuable cultural and environmental resources that are present there.