A coral record of radiocarbon variability in seawater from the Galapagos shows a step change in radiocarbon values across the 1976 climate shift, associated with a similar rise in sea surface temperature during the season of maximum upwelling. We present a simple model of water transport and mixing in the equatorial Pacific that is used to simulate radiocarbon variability to compare with the coral data. The results indicate that the velocity of the Equatorial Undercurrent (EUC) is the dominant mechanism responsible for the pattern of variability observed in the coral record, suggesting that decadal variability in the EUC may be an important component of decadal variability in Pacific and global temperature.