oa The Paleocene-Eocene Thermal Maximum at IODP Expedition 378 Site U1553, Campbell Plateau, Southern Pacific Ocean

A series of geochemical analyses (including biomarkers, isotopes and mineralogy) on IODP Expedition 378, Site U1553 were conducted to assess the PETM from an organic geochemistry perspective on the Campbell Plateau, New Zealand. During the PETM, carbon isotope ratios of bulk sediments measured separately at the Guangzhou Institute of Geochemistry, Bremen, and Kochi are consistent (-0.2 to 2‰), with a negative maxima at ∼ 56 Ma (∼482 CCF-A m). Early Palaeocene samples have a typical marine distribution of glycero dialkyl glycero tetraethers (GDGTs), so the GDGT-based paleotemperature proxy (TEX86) is considered reliable, and indicates sea surface temperatures (SST) of 18–24°C. However, the GDGT distribution in the PETM indicates mixed input from marine and other sources (e.g. deep water, terrigenous input) based on the branched and isoprenoid tetraether index (BIT) and the methane index (MI) (> 0.3), thus leading to unreliable TEX86 values in most of the samples. The highest SST in the PETM based on TEX86 is about 32°C, which disagrees with the results of the bulk carbonate clumped isotope thermometer that gives a consistent temperature of 19.8–24.4°C across the PETM, with diagenesis being a potential cause.