[S-GL17] Geochronology and Isotope Geology

[SGL17-P08] Marine osmium isotopic variation in the early Paleogene recorded in deep sea sediments of the Campbell Plateau, South Pacific Ocean

*Yusuke Hatakeyama¹, Yusuke Kuwahara^1,2, Kazutaka Yasukawa¹, Moei Yano^2,1, Kazuhide Mimura^2,1, Junichiro Ohta^1,2, Erika Tanaka^3,2, Kentaro Nakamura^1,2, Kato Yasuhiro^1,2 (1.School of Engineering, University of Tokyo, 2.Ocean Resources Research Center for Next Generation, Chiba Institute of Technology, 3.Marine Core Research Institute, Kochi University)

Keywords:Paleocene-Eocene Thermal Maximum, North Atlantic Igneous Province, Chemical weathering, Os isotope ratio, International Ocean Discovery Program

The Paleocene-Eocene Thermal Maximum (PETM) is known as the most prominent global warming event in the Cenozoic era [1]. The PETM is characterized by a rapid increase of global temperature and a distinct negative anomaly in carbon isotopic ratio, indicating a massive injection of isotopically lighter carbon into the Earth's surficial system [1-3]. Although various candidates have been proposed as its cause, the detailed mechanisms of the onset and recovery of the PETM are still in debate. Nevertheless, it is widely accepted that the massive eruption of the North Atlantic Igneous Province (NAIP) should have been involved with the PETM onset as a triggering event [2-3].
Chemical weathering of silicate minerals is one of the mechanisms that should have contributed to the termination of the PETM. Silicate minerals react with CO₂ through chemical weathering and resulting HCO₃^– forms calcium carbonate in the ocean [4]. This reaction is promoted in warm and humid climate, and is considered to act as a negative feedback on global warming by consuming atmospheric CO₂ [5].
Seawater osmium isotope ratio (¹⁸⁷Os/¹⁸⁸Os) is a useful proxy for estimating the flux of past chemical weathering [6]. Seawater ¹⁸⁷Os/¹⁸⁸Os are determined by a mixture of continental, mantle, and cosmogenic Os fluxes. Given that the cosmogenic flux is held constant on a short time interval such as the PETM, the seawater Os isotopic composition is expected to have varied with the balance between the continental flux (i.e., chemical weathering) and mantle flux (i.e., NAIP activity).
In this study, we analyzed Os isotopic composition of deep-sea sediment samples recording PETM collected from the International Ocean Discovery Program Expedition 378 Site U1553 Hole C, on the Campbell Plateau in the South Pacific Ocean. Based on the analytical results, we will discuss the changes in chemical weathering flux of continental silicates and NAIP volcanic activity around the PETM.