Depositional fluxes, palaeoproductivity, and ice rafting in the NE Atlantic over the past 30 ka


  • B. Manighetti,

  • I. N. McCave


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°N to 60°N along 20°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 terrrigenous 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.