HR: 14:20h
AN: PP43D-03 INVITED    [Abstracts]
TI: Neogene and Eocene Ice-Rafting in the Central Arctic
AU: * St. John, K E
EM: stjohnke@jmu.edu
AF: James Madison University, Dept of Geology and Environmental Science, MSC 6903, Harrisonburg, VA 22807, United States
AB: The Cenozoic ice-rafted debris (IRD) history of the central Arctic is reconstructed utilizing the terrigenous coarse sand fraction in IODP 302 cores from 0-273 mcd, which spans the depth range of the granule/pebble distribution in the split cores identified by the scientific party. This Holocene-middle Eocene quantitative record of terrigenous sand accumulation on the Lomonosov Ridge, along with qualitative information on grain texture and composition, confirm the interpretation that ice-initiation (sea ice and glacial ice) occurred ~46 Ma in the Arctic, and provides a long-term pattern of Arctic ice-expansion and decay since the middle Eocene. IRD mass accumulation rates range from 0 to 0.13 g/cm2/kyr in the middle Eocene and from 0 to 0.36 g/cm2/kyr in the Neogene. IRD MAR maxima in the Miocene and Pliocene co-occur with either glacial initiations or intensifications in the sub-Arctic. Patterns of high IRD flux in the Eocene are compatible with obliquity forcing (Sangiorgi et al., in press). A quasi-cyclic pattern of IRD input since 14 Ma with a frequency between 0.5-2 myr, suggesting that Arctic ice growth and decay was also influenced by long-term eccentricity forcing. The 46.25 Ma IRD onset in the central Arctic slightly precedes the earliest evidence of ice in the Antarctic, and compares in timing with a 1000 ppm decrease in atmospheric concentrations of CO2. The decline of pCO2 in the middle Eocene may have driven both poles across the temperature threshold that enabled the nucleation of glaciers on land and partial freezing of the surface Arctic Ocean, especially during times of low insolation.
DE: 0732 Icebergs
DE: 0750 Sea ice (4540)
DE: 4207 Arctic and Antarctic oceanography (9310, 9315)
DE: 4926 Glacial
DE: 9604 Cenozoic
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting