San Nicolas Island is a strange, far-away place very familiar to a surprising number of Californians. Thanks to Scott O'Dell's Island of the Blue Dolphins, this island — the most remote of California's eight Channel Islands — and it's native Nicoleño people have been engrained into the imaginations of many elementary school children. My own mind was captivated by this story in the fourth grade when I had the opportunity to conduct fieldwork on San Nicolas Island with Daniel Muhs (U.S. Geological Survey) and my adviser Seth Finnegan in July 2015 I was thrilled! Descending from hundreds of feet above the island’s landing strip I was already able to spot the very reason for my fieldwork- Pleistocene fossil beaches.
Carved by the powerful energy of ancient waves, over 11 Pleistocene fossil beaches are terraced (hence their geological name "marine terrace") over the landscape of San Nicolas Island's modest 23 square miles. The youngest fossil beach (~80,000 years old) sits just above present-day sea level and the oldest (~1,200,000 years old) lies atop the island's highest elevation. Fossil mollusc shells — very similar to the kinds you find along California beaches today — abound within these marine terraces. Differences in the species compositions and abundance of these mollusc shells record dynamic ecological changes that occurred in response to glacial-interglacial climatic change during the Pleistocene.
My goal on San Nicolas Island is to collect fossil shells from the lowest three marine terraces — which record the last full interglacial cycle (~120,000 – 80,000 years ago). In particular, I am collecting well-preserved fossil Callianax biplicata (common name, purple olive shell) specimens. Using these fossil shells, I am reconstructing paleoenvironmental conditions during the last interglacial period through the use of stable isotopes. The reason this is possible is because shells grow by semi-continuously depositing layers of calcium carbonate. In the same way scientists use tree rings to chronicle the life a tree, I am using shell growth layers to reconstruct the environmental conditions experienced during the lives of molluscs that lived during the last interglacial period.
After collecting fossil C. biplicata from the terraces of San Nicolas Island, Sydney Minges (UCB Integrative Biology and Earth Planetary Sciences undergraduate student) and I sampled tiny holes along shell growth lines and analyzed these samples for carbon and oxygen stable isotope ratios at UC Berkeley's Center for Stable Isotope Biogeochemistry. Taken together, these isotope ratios can be used to reconstruct changes in seasonal, annual, and inter-annual seawater conditions and temperature during the last interglacial period. When combined with paleoecological species abundance and composition data, these paleoenvironmental data will allow me to test whether species lived in environmental regimes during the last interglacial period that are quite different from conditions they experience today, or whether species have tracked their environmental niches from the last interglacial period to the present day.
San Nicolas Island is only one of my dissertation study areas. Ultimately, I hope to reconstruct the paleoenvironmental and paleoecological conditions of the last interglacial period along much of the coast of southern California. The uniqueness of this Channel Island's geology and biota will leave a lasting impression. Aside from its extensive marine terraces and rich archaeological record, San Nicolas Island also boasts ghostly caliche forests, adorable dwarfed gray foxes called "island foxes", and some of the most pristine rocky intertidal habitats in southern California. Through my work reconstructing the paleoenvironmental and paleoecological characteristics on San Nicolas Island and elsewhere in southern California, I hope to establish a pre-human baseline for how shallow marine environments respond to climate change.
This work is generously supported by grants from The UC Museum of Paleontology, National Sigma Xi, Berkeley Chapter of Sigma Xi, The UC Berkeley Department of Integrative Biology, The Evolving Earth Foundation, The American Philosophical Association, the American Association of Petroleum Geologists, the American Museum of Natural History, and the Geological Society of America.