Benthic foraminiferal records of natural and anthropogenic environmental change in a coastal estuary: Tomales Bay, CA

Tomales Bay (~50km north of San Francisco) is a low-inflow, seasonally hypersaline estuary on the Northern California coast that has been heavily influenced by anthropogenic processes (cattle ranching, land use changes, recent changes in salinity and pH). To investigate the linkages between human developments and environmental changes that have occurred in Tomales Bay, eight sediment cores (2.51m to 2.86m in length) have been recovered along the length of the bay. Sediment accumulation rates for the bay range from 2.95mm/yr to 6.27mm/yr. In the outer bay, the benthic foraminiferal assemblage is characterized by a recent (upper 30 cm) increase in agglutinated foraminifera along with a decrease in calcareous species (Elphidium hannai, Elphidium sp., Ammonia beccarii and Buccella tenerrima) following a period where calcareous species dominated the assemblage and agglutinated foraminifera populations were practically non-existent. These trends may indicate changes in saturation levels of calcite in the estuary. Benthic foraminiferal geochemistry (δ18O and Mg/Ca) will be utilized to reconstruct salinity and temperature records for the past 456 years. Comparing these findings to the well-documented history of human activity of Tomales Bay may provide insights into natural and anthropogenic environmental changes and impacts on coastal environments.