Collaborative Research: Dating Ancient Shorelines Using Amino Acid Geochronology to Reconstruct Past High Sea Levels

Global sea level has fluctuated throughout Earth history. To understand sea level changes, it is important to identify and date ancient marine shorelines. This study focuses on the Last Interglacial period about 125,000 years ago, when global sea levels were roughly 20 feet higher than today. The project improves a dating method based on chemical changes in fossil shells and applies it to a range of global sites. A publicly accessible framework and interactive tools will make it easier to determine shoreline ages in other regions. The project strengthens access to specialized research facilities and trains students in STEM fields. Improved shoreline dating will support better models of ice-sheet stability, coastal change, land uplift, and related natural hazards. This research will calibrate and standardize amino acid racemization (AAR) geochronology for marine mollusk shells by analyzing D/L ratios from approximately 100 globally distributed, independently dated Last Interglacial sites. These data will be used to establish temperature-dependent isochrons, with a primary focus on Marine Isotope Stage 5e (~125,000 years old). A complementary isochron for ~40,000 years will be derived by interpolating between Last Interglacial benchmarks and radiocarbon-dated Holocene shells, providing a tool for identifying samples beyond the effective range of radiocarbon dating. Post-depositional temperature histories will be estimated using existing climate model simulations on a ~200 km global grid to quantify spatial variation in racemization rates. Taxonomic effects will be evaluated through analyses of co-occurring taxa subjected to similar thermal histories. The study will emphasize measurements of the intra-crystalline amino acid fraction to enhance reliability and remove effects from contamination. The resulting empirical D/L–temperature relationships will underpin an interactive world map that provides predicted values and uncertainties, thereby delivering a standardized and transferable framework for shoreline AAR geochronology worldwide. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria. NSF Award ID: 2536604 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Darrell Kaufman | Institution: Northern Arizona University, FLAGSTAFF, AZ | Award Amount: $358,360 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2536604 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2536604.html