Reconstruction of Ocean Sea Surface Temperatures During the Last Major Sea Level Rise

 A 1.2 meter thick marine terrace deposit is exposed along cliffs at Crystal Cove State Park, Orange County, California.  This terrace marks the last major high stand of the sea, correlating with marine oxygen isotope sub-stage 5e (121-133ka).  The terrace deposit consists of interstratified 0.2 to 0.3 meter thick, moderately to well sorted, coarse to medium grained sand and 0.3 meter thick intervals of fragmented clams in medium to coarse grained sand and sandstone. The contorted Monterey Formation underlies the terrace deposit and a poorly sorted, moderately to poorly stratified, mostly matrix-supported debris flow unit overlies it.  Well preserved clam fragments in the terrace sequence largely range up to 2.5 cm wide and are composed of CaCO₃.  Clams present are used to reconstruct ocean temperatures using an innovative clumped isotope technique developed at the California Institute of Technology. This new technique can be used to more accurately determine ocean temperatures during the development of 5e marine terrace. Isotopic analysis of the clams indicates that ocean sea surface temperatures during terrace development ranged from 21-26^oC in comparison to the modern mean annual ocean temperatures of ~17^oC recorded at Newport Beach by NOAA. My results, which are the first reported for the clams using this geochemical technique, show that ocean temperatures were generally 7^oC to 9^oC warmer than previously reported in some studies. Additional isotopic analysis of clams in the terrace will lead to better refinement of sea surface temperatures in the Orange County area during the last major sea level rise.