143-million-year seawater osmium isotopic record: Trends, rhythms, and dynamics of volcanism and tectonics.

Tectonic events and volcanic pulses forming large igneous provinces (LIPs) have altered Earth's paleoclimate. Osmium (Os) and strontium (Sr) isotopic ratios are key tracers of past continental weathering and LIP eruptions. However, limited Cretaceous seawater Os and riverine Os-Sr data have hindered quantitative reconstructions. In this study, we present a long-term Os isotopic record from the Cretaceous to the present, revealing ~10- to 20-million-year cycles during the Cretaceous that align with rhythmic LIP eruptions. Seawater Os-Sr isotopic trends indicate transitions in continental weathering patterns during the Late Cretaceous [~90 million years ago (Ma)] and Paleogene (~35 Ma) ascribed to intensified weathering of interior Gondwana during the opening of the Atlantic Ocean and the uplift and glaciation of the Himalaya, respectively. Our Os isotopic record highlights its utility in tracing long-term LIP cycles and identifying major paleogeographic turning points.