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

Seawater (234)U/(238)U provides global-scale information about continental weathering and is vital for marine uranium-series geochronology. Existing evidence supports an increase in (234)U/(238)U since the last glacial period, but the timing and amplitude of its variability has been poorly constrained. Here we report two seawater (234)U/(238)U records based on well-preserved deep-sea corals from the low-latitude Atlantic and Pacific Oceans. The Atlantic (234)U/(238)U started to increase before major sea-level rise and overshot the modern value by 3 per mil during the early deglaciation. Deglacial (234)U/(238)U in the Pacific converged with that in the Atlantic after the abrupt resumption of Atlantic meridional overturning. We suggest that ocean mixing and early deglacial release of excess (234)U from enhanced subglacial melting of the Northern Hemisphere ice sheets have driven the observed (234)U/(238)U evolution.