Late Glacial and Holocene palaeocurrents around Rockall Bank, NE Atlantic Ocean


  • B. Manighetti,

  • I. N. McCave


Core samples and hydrographic data from 50° to 60°N and 15° to 25°W in the Northeast Atlantic Ocean are used to study changes in current activity from the last glacial to present. We establish a new method to distinguish between the effects of changing bottom current speed and varying size input by drawing upon sediment flux data and detailed grain size analysis. Changes in current speed are recorded by the mean size of the sortable (coarse) noncarbonate silt component, which increases with current vigor by winnowing away of fines. Our method involves the definition of an ideal sortable silt “input function”, recorded at a site accumulating unmodified pelagic flux only. The ideal profile is then compared with records from other sites to determine the history of current speed at a range of water depths. The upper surface of Southern Source Water (SSW) probably shoaled during the glacial, as indicated by the covariation of sortable silt records from sites presently covered by SSW and Lower North Atlantic Deep Water (LNADW). The data suggest that production of LNADW was suppressed during the glacial, increased following the last glacial maximum, and declined at the start of Termination 1A. A second pulse of production occurred immediately before the Younger Dryas event. Intermediate waters were generally faster-flowing during the glacial and may have expanded their depth domain, such that a single glacial intermediate water mass covered depths from 1100 to more than 2000 m.