RADIOMETRICALLY DETERMINED SEDIMENTARY FLUXES IN THE SUBPOLAR NORTH-ATLANTIC DURING THE LAST 140,000 YEARS

We have examined the record of sediment input during the last 140000 y ears in a deep-sea core from 49 degrees 27'N, 22 degrees 16'W in the e astern North Atlantic. Using uranium-series disequilibria to constrain time, we have calculated mass fluxes of total sediment, as well as ma ss and particle fluxes of major sedimentary components. Sediment accum ulation rates were generally lower and relatively constant during broa dly defined interglacial intervals, driven primarily by the burial of biogenic material. Accumulation rates were higher and more variable du ring glacial intervals, and were influenced primarily by terrigenous m aterial. Peaks in bulk mass fluxes were associated with particular epi sodes (Heinrich events) within the last glacial and during each of the last two deglaciations. The flux of ice-rafted debris, as uniquely id entified by coarse detrital fragments, was higher during layers repres enting each of the glacial Heinrich events, with modest increases duri ng events H3 and H6 and dramatic increases during the others, confirmi ng the widespread interpretation of these layers as episodes of enhanc ed iceberg delivery. The burial flux of foraminifera was markedly lowe r during each of the glacial Heinrich events, also confirming the orig inal identification of these layers as barren intervals. Ice-rafting e vents within marine isotope stage 5 left neither a large detrital nor biogenic flux imprint at our study site. Variations in the burial rate s of non-carbonate sediments were largely responsible for overall chan ges in sediment accumulation throughout the last climate cycle. Ice-ra fting was apparently an important delivery mechanism for this terrigen ous material. The instantaneous chronometer established here for the l ast 140000 years in the subpolar North Atlantic allows the transformat ion of existing and subsequent data from relative values to absolute b urial fluxes. (C) 1998 Elsevier Science B.V.