Deep current-controlled sedimentation in the western North Atlantic

Abstract With its multiple sources of sediment and bottom water, the North Atlantic experiences more active redistribution of sediments than most other ocean basins. North Atlantic bottom waters originate around Antarctica, in the Norwegian Sea, the Mediterranean, and the Labrador Sea. Sediment is supplied from continental land-masses, oceanic islands (notably Iceland) and from surface biological production. The water movements are controlled principally by differing densities of the water masses, and the currents tend to follow the contours of the sea floor. Where interfaces of steep density gradient intersect the seafloor, internal tides and high-frequency internal waves may also resuspend sediments. The Gulf Stream, and warm-core and cold-core mesoscale eddies with clockwise (anti-cyclonic) and anticlockwise (cyclonic) circulation, apparently contribute to the variability of current velocity at great depths and help to erode and redistribute sediments. The most important depositional products of this current activity are the great “sediment drifts” of the region (see Plate 2). These features probably contain a detailed but as yet poorly known record of the fluctuations in bottom-current activity of the North Atlantic. They have formed principally since the beginning of the Oligocene, when strong abyssal circulation began in the North Atlantic (Ewing and Hollister 1972; Tucholke and Mountain, 1979; Miller and Tucholke, 1983). The precise relationship of the drifts to the present abyssal current regime is not clear because details of that regime are poorly known. Few long-term, deep current-meter records have been taken and most of these are not adjacent to drifts.