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Paleo Slide Set: Heinrich Events: Marine Record of Abrupt Climate Changes in the Late Pleistocene
Figure showing the processes by which ice rafted detritus are deposited and transported.
While icebergs containing debris are unusual, they nevertheless figure prominently in the study of Heinrich events. The ice rafted detritus that ends up on the ocean floor originates as basal sediments (till) plucked from the bedrock substrate at the bottom of an ice sheet. The basal sediments are transported within ice streams from the middle of the ice sheet to calving ice sheet margins that extend to the shelf break. Once the basal sediments are transported to the ice sheet margin, the material is either transported as debris layers within icebergs or released into the ocean and transported to the ocean floor as debris slides or turbidites.

Changes in the basal temperature of the ice sheet can result in the freezing-on of sediments which then become entrained to the basal layer. As the ice sheet flows, these entrained sediments move up and out toward the surface of the ice margin. Both basal and entrained sediments are carried seaward as bands in icebergs (like those in previous slides). As portions of the ice sheet overhanging the ocean break off, they become icebergs drifting in the main surface currents independent of the ice margin. In these distal ice areas, sediment deposition is dominated by glacial sediments (lithics) melting out of the icebergs.

Meanwhile, meltwater at the base of the fast moving ice stream rises at the ice front. This meltwater forms a plume with a high concentration of suspended sediment. These sediments "rain out" or sink as the meltwater plume mixes with ocean water and thins seaward.

Finally, on east-facing continental margins, western boundary currents can erode and redistribute sediment, forming a nepheloid layer. (The nepheloid layer is often augmented by turbidite activity).

Photo Credits:
John T. Andrews, Thomas G. Andrews
NOAA Paleoclimatology Program and INSTAAR, University of Colorado, Boulder

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Last Modified: 12 October 2001

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