Contourite deposition on the Blake Outer Ridge has been influenced by fluctuations in the intensity of the Western Boundary Undercurrent. In particular, changes in the mean silt grain size of the contourites at the crest of the ridge reflect these fluctuations. Continuous hydraulic piston coring allowed a core that is nearly 400 m to be recovered at DSDP Site 533. Electronic particle size analysis of the detrital silt in samples from Site 533 indicates changes in the nature of North Atlantic Deep Water circulation since the mid-Pliocene. Pleistocene and Pliocene mean grain size records are distinctly different. The Pleistocene record is characterized by large amplitude oscillations around an average grain size of 15.87 um, while Pliocene grain sizes vary at lower amplitudes around an average size of 14.87 um. Major fluctuations in Pleistocene grain size probably reflect the response of North Atlantic circulation to glacial and interglacial cycles. Low-amplitude variation in the Pliocene grain size record correlates well with the relatively less variable Pliocene climate. The transition marking the onset of the Pleistocene pattern of glacial and interglacial fluctuations occurs in the late Pliocene. This transition is between the last appearence datum of Discoaster tamilis at 2.65 Ma and the last appearance datum of Discoaster pentaradiatus around 2.33-2.43 Ma (Backman and Pestiaux, 1987). The timing of this change in the grain size pattern suggests that it is related to the glacial event at 2.37 Ma identified by Shackleton et al. (1984). The % CaCO (sub 3) record resembles the grain size record because it also varies at low amplitudes during the Pliocene and at high amplitudes during the Pleistocene. Percent CaCO (sub 3) in marine sediments is affected by oceanographic conditions which respond to climatic change. In particular, low percentages of CaCO (sub 3) are associated with glacial episodes in the North Atlantic Basin. At DSDP Site 533 CaCO (sub 3) deposition shifts from Pliocene to Pleistocene conditions above the LAD D. pentaradiatus (2.33-2.43 Ma), probably in response to the onset of Northern Hemisphere glaciation. Therefore, correlation between trends in grain size and % CaCO (sub 3) strengthens the idea that fluctuations in the ....