HR: 0800h
AN: OS41D-0515    [Abstracts]
TI: Preservation and Alteration of the 1995 Eel River Flood Deposit
AU: Richey, C A
AF: Department of Oceanography, Humboldt State University, 1 Harpst Street, Arcata, CA 95521-8222 United States
AU: Bodenhamer, C
AF: Department of Oceanography, Humboldt State University, 1 Harpst Street, Arcata, CA 95521-8222 United States
AU: Borgeld, J C
AF: Department of Oceanography, Humboldt State University, 1 Harpst Street, Arcata, CA 95521-8222 United States
AU: Brower, J
AF: Department of Oceanography, Humboldt State University, 1 Harpst Street, Arcata, CA 95521-8222 United States
AU: Genger, H M
AF: Department of Oceanography, Humboldt State University, 1 Harpst Street, Arcata, CA 95521-8222 United States
AU: Hayduk, L A
AF: Department of Oceanography, Humboldt State University, 1 Harpst Street, Arcata, CA 95521-8222 United States
AU: Ryan, T W
AF: Department of Oceanography, Humboldt State University, 1 Harpst Street, Arcata, CA 95521-8222 United States
AU: Slimmer, M D
AF: Department of Oceanography, Humboldt State University, 1 Harpst Street, Arcata, CA 95521-8222 United States
AU: * Westman, V
AF: Department of Oceanography, Humboldt State University, 1 Harpst Street, Arcata, CA 95521-8222 United States
AB: The Eel River shelf of northern California is episodically subject to seasonal flood events and associated sediment deposition. Flooding of the Eel River in the winter and spring of 1995, and the winter of 1997, resulted in a recognizable sequence of layers deposited across much of the adjacent continental shelf. Event-response sampling allowed the short term fate of the deposits to be documented (Wheatcroft, 2000). Within a few years after the 1997 event, the flood deposit was mixed or remobilized such that the original deposit was not recognized in core x-radiographs anywhere on the shelf. However, remnants of the 1995 flood deposit were still identifiable as of October 2001 (Wheatcroft {\it et al}., in progress). In May 2004, a total of 31 box cores were collected at 23 different stations along transects established by previous studies. Flood layers were still present and recognizable in x-radiographs at several stations. Many of the layers identified in x-radiographs were, although preserved, visibly disrupted. In locations where x-radiographs were inconclusive, the unusually fine-grained nature of the deposit allowed them to be detected using standard sediment size analyses. The mean percent of sediment $<$20 $\mu$m ranged from 68-84% in the 1995 flood deposit. Core subsamples were analyzed from the upper 16 cm in order to determine biological abundance. Polychaete worms were identified as the dominant taxonomic group, constituting approximately 80% of the identified organisms, which is consistent with previous research (Wheatcroft {\it et al}., in progress; Bentley and Nittrouer, 2003). The dominance of polychaetes is notable in light of the fact that these subsurface deposit feeders are likely to mix sediment to substantial depths (Wheatcroft {\it et al}., in progress). Despite this biological activity, the flood layer is still recognizable a decade after the initial event. As a result, the 1995 flood deposit may ultimately become a permanent piece of the stratigraphic record.
DE: 4804 Benthic processes/benthos
DE: 4863 Sedimentation
DE: 4299 General or miscellaneous
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting