Abstract
<title>Abstract</title> <p>The Hirnantian Age (Late Ordovician) witnessed the first glaciation of the Phanerozoic and the second-largest mass extinction in Earth history1,2. Yet the climatic evolution during the subsequent deglaciation has remained poorly understood, as most sedimentary records are too condensed to resolve short-term environmental changes3,4. Here we show, using high-resolution geochemical analyses from a rapidly deposited shallow-water succession on the Tarim Palaeoplate, that the post-glacial interval was characterized by seven millennial-scale cold–warm cycles with a mean periodicity of ~17,000 years. These oscillations, driven by multi-episodic discharge of the Palaeo-Antarctic ice sheet, generated cold-water currents that reached the tropical Proto-Tethys—a mechanism directly analogous to Cenozoic Heinrich events5. Our findings demonstrate that ice-sheet instability on millennial timescales is not a unique feature of the Pleistocene, but a fundamental process dating back to the first Phanerozoic glaciation. Moreover, these cooling pulses constrained the biogeographic distribution of pioneer faunas that emerged after the mass extinction, revealing that glacial discharge influenced tropical biotic recovery patterns far earlier than previously recognized.</p>