2004 Denver Annual Meeting (November 7–10, 2004)

Paper No. 1
Presentation Time: 1:30 PM


DUNHILL, Gita, INSTAAR, University of Colorado, Boulder, CO 80304, dunhill@colorado.edu

Denmark Strait located between Iceland and Greenland is a critical study area because slope sedimentation is a result of oceanographic conditions, climate, and ice dynamics. The interaction of these elements through glacial/interglacial cycles determines the nature of the marine sedimentation. This study aims to unravel the oceanographic, climatic, and sedimentary history of the Southwestern Iceland Slope over the last 200 kyr derived from an 18-meter marine core from Snorri Drift.

The depositional processes that contribute to the formation of Snorri Drift such as iceberg rafting (IRD) and bottom current (BC) activity reflect ice sheet movement and deep- water convection. Stadials 2, 4 and 6 were times of dominant iceberg rafting. The δ18 O data suggest that Stage 2 and 6 were relatively cold stadials compared to St. 4. Although St. 2 and 6 were equally cold stadials, the IRD record suggests different glaciological responses to the climate conditions. The sediments of St. 6 have less IRD than those of the St. 2. Although there are at least three major IRD pulses during St. 6, the low background levels indicate that the there was a sea ice cover which prevented iceberg deposition.

About 90 kyr ago there was a distinct change in how the Greenland Ice Sheet (GIS) produced icebergs in response to insolation changes. Prior to then iceberg production was cyclical with pulses occurring 2-6 kyr after insolation maximums, which suggests that the GIS required time to equilibrate and produce icebergs. Since then, the GIS’s response to changes in insolation seems independent of insolation trends.

During the interstadials deposition by bottom currents appears to be more active on Snorri Drift. During the Holocene, the warmer intervals of stage 3 and 6, and 5e sedimentation was significantly affected by the strong northward flowing Atlantic deep water. These sediments are well sorted with a strong silt mode indicative of current deposition. Current speed proxies suggest that BC’s accelerated during deglaciations and increased during warm periods, including the Holocene when some of the strongest flow is recorded. This increase in BC activity suggests that North Atlantic Deep Water convection was more active during the interglacials than during the glacials, during which time iceberg rafting was the more dominant depositional process.