DEPOSITIONAL FLUXES, PALAEOPRODUCTIVITY, AND ICE RAFTING IN THE NE ATLANTIC OVER THE PAST 30 KA

Over the last 30 ka, sediment flux to the northeast Atlantic Ocean has been strongly influenced by the growth and decay of northern hemisphere ice sheets, input of ice-rafted detritus, the migration of the polar front, and associated changes in patterns of biological productivity. We examined cores from 47 degrees N to 60 degrees N along 20 degrees W to determine the flux of components including carbonate, organic carbon and terrigenous material and divided into size fractions. During the glacial period, fine carbonate flux was low and ice-rafted input high. Burial flux during the Holocene became dominated by coccolith and foraminiferal carbonate, with minor organic matter and biogenic silica. Estimates of palaeoproductivity are ambiguous: a method which corrects for water depth and sedimentation rate suggests no clear glacial to Holocene change, whereas a method based on percentage of organic carbon suggests increased productivity from glacial to Holocene of around 60%. Sites of sediment focusing saw a change from enhanced fine terrigenous flux in the glacial to enhanced fine carbonate in the Holocene. After compensating for sediment focusing, glacial ice-rafted flux distribution shows a decrease from south to north across the area, reflecting cyclonic surface water circulation. Deposition of ice-rafted detritus during Heinrich events H1 and H2 led to enhanced preservation of organic matter immediately beneath the layers, indicating a rapid accumulation rate.