Hafnium isotope stratigraphy of ferromanganese crusts

A Cenozoic record of hafnium isotopic compositions of central Pacific deep water has been obtained from two ferromanganese crusts. The crusts are sepa rated by more than 3000 kilometers but display similar secular variations. Significant fluctuations in hafnium isotopic composition occurred in the Eo cene and Oligocene, possibly related to direct advection from the Indian an d Atlantic oceans. Hafnium isotopic compositions have remained approximatel y uniform for the past 20 million years, probably reflecting increased isol ation of the central Pacific. The mechanisms responsible for the increase i n Sr-87/Sr-86 in seawater through the Cenozoic apparently had no effect on central Pacific deep-water hafnium.