Biomarker Preservation and Paleoclimate from Late Neogene Marine Sediments from DSDP Site 467 offshore Los Angeles

The Neogene encompasses warm periods of Earth's History that provide analogues for future warming. In southwestern North America, concerns regarding future warming are compounded by uncertainty about whether the current drying trend will continue. Today, the cool California current and upwelling results in sea surface temperatures (SST) of ~14˚C while past warmer states might have fed convection and increased rainfall. Here, we revisit Deep Sea Drilling Project Site 467, outside the Santa Barbara Basin (33°50.97'N, 120°45.47'W, 2,127.8 m water depth), drilled in 1978. We identify and quantify marine and terrestrial biomarkers in 108 samples spanning 16.7 to 3.6 Ma. We identified the loss of preservation of alkenones below 413 mbsf (5.0 Ma) and loss of GDGTs below 587 mbsf (7.9 Ma). The alkane fraction includes an uncharacterized complex mixture, indicating maturation and biodegradation. In contrast n-alkanoic acids were abundant throughout the profile, suggesting post-deposition production. Although preservation curtails the record, GDGTs indicate cooling from 23 to 17°C from 8.2 to 3.6 Ma that is consistent with regional alkenone reconstructions. Alkenones are only preserved in the Pliocene and yield estimates around 25°C that appear warm-biased, consistent with preferential loss of C37:3. Elsewhere reports of reduced organic carbon burial in the middle Miocene presents a challenge for efforts to use organic biomarkers to reconstruct this relatively recent warm climate analogue.