Volcanic forcing of global climate cooling at the Younger Dryas onset preserved in North American sediments

The Younger Dryas (YD; ~12.9 to 11.7 thousand years) marks an abrupt return to near-glacial conditions during the last deglaciation, yet its cause remains debated. One possible scenario, the YD impact hypothesis, proposes an extraterrestrial trigger. However, growing geochemical and stratigraphic evidence points toward a volcanic origin. This study presents the 187 Os/ 188 Os isotope and highly siderophile element (HSE) data from the Page-Ladson (PL) site (8JE591) in Florida, a well-dated, continuous sedimentary record spanning the YD onset. The onset in the PL profile is marked by unradiogenic osmium coincident with elevated Os and Re concentrations and a Cl-chondrite–normalized HSE pattern with a compositional range and signature closely matching volcanic aerosol patterns. When integrated with comparable records from Hall’s Cave and the Debra L. Friedkin site in Texas, the unradiogenic 187 Os/ 188 Os ratios align across multiple depositional environments and correlate with a cluster of major bipolar volcanic eruptions (~12.98 to 12.87 thousand years) documented in Greenland and Antarctic ice cores whose cumulative radiative forcing exceeds the most volcanically active intervals of the Common Era. The magnitude and hemispheric asymmetry of this volcanic activity imply forcing of sufficient magnitude capable of disrupting the Atlantic Meridional Overturning Circulation and triggering rapid Northern Hemisphere cooling. These findings provide multiproxy, regionally consistent evidence for a volcanically driven perturbation at the onset of the YD, offering a robust alternative to impact-based explanations.