HR: 1330h
AN: OS52A-0903    [PDF]
TI: Snorri Drift: A Comparison of Stadial 2 and Stadial 4 on the SW Iceland Slope
AU: * Dunhill, G
EM: dunhill@colorado.edu
AB: Preliminary investigations of an 18 meter marine core collected from the southwest Iceland slope south of Denmark Strait reveal a coherent record reaching back to oxygen isotope stage 7. The core provides a rare opportunity to study the environmental and oceanographic conditions just south of Denmark Strait over the last 200k years. Oxygen isotope data, sedimentological analyses, grain counts, and radiogenic isotopic data enable interpretation of climatic shifts, sediment source, as well as changes in the strength and direction of the bottom currents. Core MD99-2323 was collected in 1062 meters water depth from Snorri Drift, which is one of the northern North Atlantic drifts. The chronology of the core is based on radiocarbon dates, tephrachronology and an oxygen isotope curve derived from the planktic foram, Neogloboquadrina pachyderma sinistral. The 18 meter core shows a widely varying lithology with the interglacial intervals consisting of mostly muddy sand with few clasts and some laminations. Within the interstadials are abrupt coolings, which are marked by darker gray, clast rich units. The stadial units are characterized by alternating layers of dark gray clast rich intervals with a coarser matrix and lighter gray layers which have a finer matrix and fewer clasts. Often these units are somewhat laminated. Darker units are coarse and represent coolings. Lighter units are finer and represent warmings. The sediments of Stage 2 and 4 stadials reveal very different climatic conditions, sediment source and depositional processes on the Iceland slope. The d18O, foraminifera abundances, and number of ice rafted grains suggest that stage 2 was colder, more variable and unstable than stage 4 which was warmer and more stable. The radiogenic isotopes and grain counts indicate distinct sediment sources for these two stadials. During stage 2 the source appears extremely variable, but with a distinct Icelandic component, while during stage 4 the source is also variable, but with a more distal signature, possibly a Greenland source. This core represents the varying contribution from iceberg rafting and contourite deposition. The sediment of stage 2 have more IRD and larger grain sizes suggesting a higher energy transport process such as icebergs rafting. Stage 2 is during the LGM with evidence for a migrating glacial front affecting marine sedimentation. This is in contrast to the East Greenland terrestrial records, which suggest a stable Flakkerhuk stade from 60-10 ky with little ice sheet movement. In contrast, the sediments of stage 4 are finer and contain less but more consistent IRD. The finer grain size, distal source, and less IRD all suggest increased contourite deposition at this SW Iceland slope site which indicates a shift in the bottom current's direction and/or source of icebergs.
DE: 3022 Marine sediments--processes and transport
DE: 4267 Paleoceanography
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting