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

Uranium in the deep sea The ratio of 234 U to 238 U in seawater underlies modern marine uranium-thorium geochronology, but it is difficult to establish the ratio precisely. Chen et al. report two 234 U/ 238 U records derived from deep-sea corals (see the Perspective by Yokoyama and Esat). The records reveal a number of important similarities to and differences from existing records of the past 30,000 years. Higher values during the most recent 10,000 years than during earlier glaciated conditions may reflect enhanced subglacial melting during deglaciation. Science , this issue p. 626 ; see also p. 550