Ocean mixing and ice-sheet control of seawater ²³⁴U/²³⁸U during the last deglaciation

Seawater ²³⁴U/²³⁸U provides global-scale information on continental weathering and is vital for marine U-series geochronology. Previous evidence supports an increase in ²³⁴U/²³⁸U since the last glacial, but the timing and amplitude of its variability was poorly constrained. Here we report two seawater ²³⁴U/²³⁸U records based on well-preserved deep-sea corals from the low latitude Atlantic and Pacific. The Atlantic ²³⁴U/²³⁸U starts to increase before major sea level rise and overshoots the modern value by 3‰ in the early deglaciation. Deglacial ²³⁴U/²³⁸U of the Pacific converges with the Atlantic after the abrupt resumption of Atlantic meridional overturning. We suggest that ocean mixing and early deglacial release of excess ²³⁴U from enhanced subglacial melt activity of the Northern Hemisphere ice sheets have driven the observed ²³⁴U/²³⁸U evolution.