Biomarker Preservation and Paleoclimate From Late Neogene Marine Sediments From DSDP Site 467, Offshore Los Angeles

Abstract The Neogene, a warm period of Earth's history, provides analogs for future warming. In southwestern North America, concerns regarding future warming are compounded by uncertainty about the drying trend. Today, the cool California current and upwelling results in sea surface temperatures 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 14.7 to 3.8 Ma. We identified a crash in the abundance of alkenones below 413 mbsf (5.0 Ma) and in glycerol dialkyl glycerol tetraethers (GDGTs) below 587 mbsf (7.9 Ma). The low thermal maturity of the hydrocarbon fraction does not support biomarker removal by thermal cracking. Warmer SSTs, warmer bottom waters, and greater oxygenation of the water column may instead have reduced their preservation. n ‐Alkanoic acids are 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 3.8 Ma, while most cooling happens between 8 and 7 Ma, consistent with other alkenone reconstructions in the region. In this core, alkenones were only detected in the Pliocene and yield estimates around 25°C that appear warm‐biased, suggesting preferential loss of C 37:3 . Other reports of reduced organic carbon burial in the middle Miocene present a challenge for efforts to use alkenone and GDGT biomarkers to reconstruct this relatively recent warm climate analog.