LATE-GLACIAL AND HOLOCENE PALEOCURRENTS AROUND ROCKALL BANK, NE ATLANTIC-OCEAN

Core samples and hydrographic data from 50 degrees to 60 degrees N and 15 degrees to 25 degrees W in the Northeast Atlantic Ocean are used t o study changes in current activity from the last glacial to present. We establish a new method to distinguish between the effects of changi ng bottom current speed and varying size input by drawing upon sedimen t flux data and detailed grain size analysis, Changes in current speed are recorded by the mean size of the sortable (coarse) noncarbonate s ilt 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 de pths, The upper surface of Southern Source Water (SSW) probably shoale d during the glacial, as indicated by the covariation of sortable silt records from sites presently covered by SSW and Lower North Atlantic Deep Wafer (LNADW). The data suggest that production of LNADW was supp ressed during the glacial, increased following the last glacial maximu m, and declined at the start of Termination 1A. A second pulse of prod uction occurred immediately before the Younger Dryas event. Intermedia te waters were generally faster-flowing during the glacial and may hav e expanded their depth domain, such that a single glacial intermediate water mass covered depths from 1100 to more than 2000 m.