Intensified bottom water formation in the southwest Pacific during the early Eocene greenhouse—Insights from neodymium isotopes

Abstract The Early Eocene Climatic Optimum (EECO; 53–49 Ma), when Earth experienced peak Cenozoic surface temperatures, provides a test case for how ocean circulation might operate under enhanced greenhouse climate conditions. The topic lies at the forefront of current geoscience, but evolution of ocean circulation during this climatic extreme remains unresolved, critically at high southern latitudes. We present the first highly resolved record of neodymium isotope values at high southern latitudes (International Ocean Discovery Program Site U1510), a proxy that tracks ocean bottom water. A prominent negative shift in seawater εNd(t) in the Tasman Sea in the middle of the EECO was likely driven by a new bottom water mass, with the Antarctic sector of the Pacific Ocean being the obvious source. Comparison with low-resolution studies from other sites in the Tasman Sea suggests that a new intermediate water source flowed farther away from the Tasman Sea and into the Pacific during the EECO. Intensification of dense water formation at high southern latitudes during peak greenhouse warmth is surprising but consistent with recent findings that highlight the complexity of global thermohaline circulation.