Intensified global volcanism during Late Pleistocene glacial strength shift

Abstract Reduced ice volume during interglacials is thought to amplify volcanic activity because ice-mass removal depressurises magma chambers¹. While this process has been detected on regional² and perhaps semi-global scales³, a lack of globally representative tephra production records leaves the global relationship between glacial-interglacial cycles and volcanism uncertain. Here, we interrogate this relationship by using a database of visible tephra layers in marine sediments⁴ and applying statistical sampling techniques to develop a globally representative tephra production record spanning the past million years. We find that explosive volcanism intensified globally at about 420 to 400 thousand years ago (ka), coinciding with Marine Isotope Stage (MIS) 11 – the warmest interglacial of the past million years when sea level was approximately 10 m above present⁵, and Greenland was largely ice-free⁶. We propose that positive feedbacks between icesheet ablation and increased volcanic carbon dioxide (CO2) outgassing may explain this warmth, and in turn, the Mid-Brunhes transition which heralded warmer interglacials⁷. Concurrently, we observe a shift to more organised volcanic cycles, characterised by higher intensity peaks, mirroring eccentricity forcing seen in ice volume records. More pronounced ice-volcano feedbacks may explain the stronger interglacials of the past 400,000 years, a crucial period of hominin evolution⁸.