| Abstract: | Biostratigraphic analysis of seven piston cores from the southeastern Blake Plateau suggests that the upper Miocene to Recent sedimentary section at this location represents a history of deposition of calcareous ooze alternating with current-induced nondeposition or erosion. This record is primarily a result of long-term fluctuations in the velocity of the western boundary current or Gulf Stream, which sweeps the plateau. High-velocity phases of this current system, as signaled by hiatuses in the section, lie within the time limits 4.8 to 6.1, 3.9 to 4.4, 2.3 to 2.9, and 0 to 1.5 million years before present (B.P.). These time intervals are coeval with dated episodes of climatic decline and glaciation. The most intense acceleration of the Gulf Stream, as indicated by deep erosion of the Blake Plateau, occurred in the latest Miocene to earliest Pliocene (4.8 to 6.1 million years B.P.) in conjunction with a major expansion of the Antarctic ice cap. Subsequent accelerations of the Gulf Stream coincide with early Pliocene cooling in the Southern Hemisphere, worldwide expansion of high-altitude-high-latitude glaciers in the late Pliocene, and the classical glaciations of the Pleistocene. An additional, protracted increase in the average velocity of the Gulf Stream, which began in the late Miocene and culminated in the mid-Pliocene (about 3.8 million years B.P.), can be attributed to the gradual emergence of the Central American isthmus. |
