研究業績

The early Paleogene, including the Paleocene and Eocene, is characterized by Warmhouse and Hothouse climate states with superimposed transient warming events known as hyperthermals. While these paleoenvironmental changes are well-documented in the Pacific and Atlantic Oceans, records of such changes in the Indian Ocean are limited. Here, we present a new data set of bulk chemical composition and stable isotopic ratios from the late Paleocene to middle Eocene sediments on the Exmouth Plateau in the mid-latitude eastern Indian Ocean. The bulk δ13C and δ18O suggest a warming period called the Early Eocene Climatic Optimum (EECO) and cooling toward the middle Eocene in a long-term perspective. In the short-term, we identified at least six hyperthermals (Paleocene–Eocene Thermal Maximum, H2, I1, J, ETM3, and L) in the studied sections. By applying independent component (IC) analyses (ICA) to the bulk chemical composition data, we identified six ICs corresponding to sediment source materials and post-depositional processes. The ICA result infers an increase in detrital materials or a decrease in carbonate rain flux, and an increased population of higher-order consumers in the oceanic ecosystem during both long-term (EECO) and short-term (hyperthermal) warmings around the Exmouth Plateau. Furthermore, ICs representing diagenetic processes and post-depositional remobilization of elements showed excursions across the hyperthermal horizons, indicating that changes in the redox state of pore or bottom water are associated with hyperthermals. This study provides critical insights into the paleoceanography of the Indian Ocean, highlighting the response of marine environments to both long-term and short-term climatic events during the early Paleogene.