The Suess Effect is a gradual decrease of the C-14/C-12 ratio in tree rings from 1870 to 1950 that is attributed mostly to the burning of C-14-free fossil fuels for energy. In contrast, pre-nuclear bomb high-precision measurements of C-14/C-12 ratios in banded corals from the North Atlantic Ocean do not exhibit the expected Suess Effect. Instead, large biennial-to-decadal shifts in the C-14/C-12 ratios appear throughout the coral records. This pattern indicates that rapid pulses of increased mixing between surface and subsurface waters occurred in the North Atlantic Ocean during the past century.