Glacial cycles significantly influenced Earth’s surface processes throughout the Quaternary, impacting the climate, sea level, and seismic and magmatic activity1–3. However, the effects of glaciation and deglaciation (that is, glacial forcing) on lithospheric motion are unknown. To study these effects, we formulated high-resolution numerical models with realistic lithospheric structures, including weak plate margins, lithospheric thickness variations and crustal structure. Our results show that glacial forcing significantly altered lithospheric motion and the spreading rates of mid-ocean ridges situated near major ice sheets in the last glacial cycle. For example, deglaciation-induced motion in the North American plate had a rotational part that was up to around 25% of its tectonic plate motion over 10,000-year timescales. The deglaciation in Greenland and Fennoscandia caused up to 40% fluctuations in the spreading rates of the Iceland Ridge between 12,000 and 6,000 years ago, which may explain the Holocene volcanism in Iceland. Our modelling also indicates increased (decreased) rates of global sea-floor production during the deglaciation (glaciation) periods with implications for mantle degassing rates. These results underscore the critical dynamic interplay between glacial cycles, lithospheric motion, ridge spreading and climate during ice ages.
