Unlocking the geochemical features of the Paleocene southern Pacific Ocean using carbon isotopes and biolipids

Little is known about the Paleocene in the southern Pacific Ocean due to scarce marine records. Here, we present a systematic geochemical investigation using biomarkers, carbonate content, and carbon isotopes of a set of early Paleocene deep-sea cores from International Ocean Discovery Program Expedition 378 Site U1553. The results provide a new Paleocene biomarker profile for the Campbell Plateau, New Zealand. The occurrence and distribution of a series of hopenes, ββ hopanes, sterenes and biomarker-based maturity parameters indicate that these organically-lean sediments are in an early diagenetic stage, with an equivalent vitrinite reflectance of approximately 0.4%. Biomarker data (e.g., gammacerane index and homohopane index), carbonate carbon isotopes (−27.9 ‰ to +2.0 ‰) combined with onboard data (sulphur and methane contents) indicate that the redox properties of the Paleocene southern Pacific Ocean changed from an oxidising-anoxic transition zone to a more reducing marine environment (water depth > 1000 m). The sources of the organic matter are diverse, including algae, bacteria, diatoms, dinoflagellates, and higher plants, but are dominated by aquatic organisms. Our new biomarker record bridges a Paleocene biosphere knowledge gap in the high latitude South Pacific.