Paper No. 26
Presentation Time: 1:30 PM-5:30 PM
THE FIRST LONG TERM RECORD OF ICE-RAFTING IN THE CENTRAL ARCTIC BASED ON SAND ACCUMULATION, 0 TO 46 MA
IODP Expedition 302 on the Lomonosov ridge recently recovered the most continuous Cenozoic sediment record of the Arctic Ocean enabling unprecedented study of the Arctic's transition from a greenhouse to an icehouse world during the last 50 myr. The Cenozoic history of ice rafting in the central Arctic can be determined by examining the terrigenous sand accumulation. Preliminary weight percent analysis was conducted on 325 samples with an average sample resolution of 64 kyr as a step towards determining the mass accumulation rate of ice-rafted debris (IRD). Point count compositional analysis for 150-250 um sediments from the Pleistocene provides a detailed analysis of the most recent ice activity and is used to specify provenance of IRD. Results place the initiation of ice at 44 Ma, consistent with the age of oldest dropstone identified by the ACEX scientific party. This pushes back the age of Northern Hemisphere ice initiation nearly 37 myr, from the accepted age of ephemeral ice of 8 Ma. The Oligocene-Miocene boundary marks a change in the temporal patterns of the central Arctic IRD accumulation; background IRD steps up to a level similar to the IRD peaks in the older sediments, and the IRD peaks from this age forward reach significantly higher magnitudes than previously seen. An increase in the relative abundance of IRD occurs at 1 Ma, reflecting the Arctic's response to the mid-Pleistocene Climate Transition. The Pleistocene IRD accumulation is dominated by clear, milky, and hematite-stained quartz, with little or no carbonates. This is in contrast to previous work in the western Arctic that describe an abundance of carbonates, thus indicating different sourcelands.