THE LATE LUTETIAN THERMAL MAXIMUM AT IODP SITE U1508 (TASMAN SEA)

The gradual cooling trend of the middle Eocene was interrupted by a global and short-lived warming event, the Late Lutetian Thermal Maximum (LLTM, ca. 42.5 Ma). This contrasts with other Paleocene and early Eocene hyperthermal events, which are superimposed on a long-term warming trend. Like other hyperthermals, the LLTM is characterized by coupled carbon and oxygen isotope negative excursions and increased pCO₂ levels. The analysis of its consequences on marine ecosystems is key to unravel climate dynamics during periods of high pCO₂ levels, but studies documenting the LLTM are scarce, and mostly focused on the Atlantic Ocean. Its short duration (ca. 10 kyr or less in the Atlantic Ocean) hinders identification in deep-sea sediments.

Here we present a quantitative benthic foraminiferal record from International Ocean Discovery Program Site U1508 to investigate for the first time the biotic turnover and paleoenvironmental changes in the deep-sea across the LLTM in the Southwest Pacific. Site U1508 is located in the northeast margin of Reinga Basin, and middle Eocene sediments were deposited at lower bathyal depths. At this site, the LLTM is marked by a sharp negative excursion of δ¹⁸O (0.4‰) and δ¹³C (1.3‰), and by a 11% drop in CaCO₃ values. However, benthic foraminiferal assemblages are dominated by calcareous taxa (≥85% in the 25 samples studied) and indicate there was not carbonate dissolution across the study interval. The paleoenvironmental interpretation points to low oxygen conditions and a high nutrient supply to the seafloor during the LLTM. This is inferred from the dominance of infaunal species, high relative abundance of dysoxic taxa (Lenticulina, Nonion), and decreased abundance of Globocassidulina subglobosa, a species that is typically related to oxic environments. Decreased diversity of the assemblages further supports environmental stress during the LLTM. Our study will contribute to understand the relative role of changes in carbon flux vs. warming during the LLTM, and to evaluate how global changes affect marine ecosystems.

Acknowledgments: Project PID2019-105537RB-I00, Spanish Ministry of Economy and Competitiveness and FEDER funds.