Constraining the applicability of organic paleotemperature proxies for the last 90 Myrs

We evaluated changes in the distributions of long-chain alkenones, long-chain diols and GDGTs, lipids commonly used for paleothermometry, over the last 90 Myrs for sediments deposited on the New Jersey shelf (the Bass River site) and assessed potential effects of different ancestral producers and diagenesis on their distributions and their impact on the associated temperature proxies. As reported before, the Paleogene distributions of alkenones are generally similar to those in modern haptophytes, but unusual alkenone distributions, characterized by a dominant di-unsaturated C ₄₀ alkenone, are observed for Late Cretaceous sediments, suggesting different ancestral source organisms for alkenones in this interval. The isoprenoid GDGT distributions remained comparable to modern-day distributions, suggesting that TEX ₈₆ can be applied up to ca. 90 Ma. The Miocene long-chain diol distributions are similar to modern-day distributions, but the older sediments reveal unusual distributions, dominated by the C ₂₈ 1,12- and C ₂₆ 1,13-diols, suggesting different source organisms before ∼30 Ma. Accordingly, the LDI does not match other paleotemperature proxies, suggesting its applicability might be compromised for sediments older than the Miocene. Our results indicate that of the three proxies, the TEX ₈₆ seems to be the most applicable for deep time temperature reconstructions.