RECONSTRUCTING LATE PLEISTOCENE PALEOENVIRONMENTS OF COASTAL CALIFORNIA: COMPARISON BETWEEN MODERN AND FOSSIL CALLIANAX BIPLICATA STABLE ISOTOPE PROFILES

Fossiliferous marine terraces formed in southern and central California during Late Pleistocene sea level stands provide a potential record of coastal environmental conditions during the last interglacial complex (Marine Isotope Stage 5; ~130 kya to ~80 kya). Most previous efforts to reconstruct Late Pleistocene paleoenvironmental conditions in this region have relied on inferences from faunal composition: the paleoenvironment is reconstructed based on the present-day environmental distributions of the species in the fossil assemblage.. However, this approach is based on the assumption that the present-day paleoenvironmental ranges of species reflect the full range of conditions under which they could live. Testing the validity of this assumption requires paleoenvironmental proxy data that are independent of faunal composition.

We examined stable isotope ratios (δO¹⁸ and δC¹³) recorded in growth lines of modern and fossil specimens of a marine gastropod, Callianax biplicata (Sowerby ,1825) to reconstruct seasonal and inter-annual variation in temperature and/or salinity during different stages of the last interglacial complex. C. biplicata is one of the most common species in both modern and fossil coastal environments, allowing us to use a locality-based approach in which we compare fossil and modern C. biplicata individuals from the same area. Our analyses are focused on localities in mainland coastal California and the Channel islands. Previous whole-shell δO¹⁸ studies have suggested that sea surface temperatures in southern California during the last full interglacial (MIS 5e) may have been cooler than present despite warmer-than-present global average temperatures. Preliminary analyses of modern and fossil C. biplicata specimens from Terrace 2 on San Nicolas Island show substantially more enriched δO¹⁸ values in fossil specimens, implying cooler and/or more saline waters relative to present. Future work will extend modern-fossil comparisons to other taxa, localities, and terraces, and will use clumped isotope analyses to independently constrain changes in salinity and water temperature.