HR: 16:15h
AN: OS44A-02    [Abstracts]
TI: Seasonal Trends in Sedimentation on the Fly River Margin: Shelf, Channel, and Open Clinoform
AU: * Crockett, J S
EM: crockett@ocean.washington.edu
AF: University of Washington, School of Oceanography Box 357940, Seattle, WA 98195 United States
AU: Nittrouer, C A
EM: nittroue@ocean.washington.edu
AF: University of Washington, School of Oceanography Box 357940, Seattle, WA 98195 United States
AU: Ogston, A S
EM: ogston@ocean.washington.edu
AF: University of Washington, School of Oceanography Box 357940, Seattle, WA 98195 United States
AB: Recent multibeam mapping and sedimentary studies on the Fly River margin, Papua New Guinea, have revealed across-shelf heterogeneity that likely impacts sediment-transport processes on the margin. Several ancient river valleys with up to 50 m of relief have been discovered and their sedimentary history provides insights to the mechanisms of channel infilling and sedimentation on this margin. Umuda channel, which is located adjacent to the Northern Entrance of the Fly River, exhibits the greatest extent of infilling, and will be a focus of this paper. Kasten ($\sim$2 m) and box ($\sim$50 cm) cores were collected during the energetic Trade-wind season (June to November), the relatively quiescent Monsoon season (December to March), and the Transition from Monsoon to Trade-wind conditions (April/May). $^{210}$Pb, x-radiograph, and grain-size analysis reveal the patterns of sedimentation within Umuda channel, and on the open clinoform to the north. The surface 150 cm of sediment in Umuda channel has relatively uniform excess $^{210}$Pb activity that abruptly decreases to background levels below $\sim$150 cm. These data suggest that the surface 150 cm were deposited relatively quickly within the last $\sim$100 y. Over the course of sampling seasons, a decrease of $\sim$10 cm was observed in the elevation of the seabed within Umuda channel. During the Trade-wind season, seabed elevation was at a maximum. Surface sediments were removed between the Trade-wind and Monsoon seasons, and again between the Monsoon and Transition seasons. This pattern is similar on the open clinoform to the north. We hypothesize that this represents a seasonal transfer of sediment from shallow to deeper water.
DE: 3022 Marine sediments--processes and transport
DE: 3045 Seafloor morphology and bottom photography
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting