Bottom and suspended particle sizes: Implications for modern sediment transport in Quinault submarine canyon

Electronic particle size analysis of suspended particulate matter and seabed sediments collected over a two-year field study of Quinault Canyon indicates that fine silts (5–9 μm modal diameter) dominate canyon sedimentation. These sediments are markedly finer than the coarse silts (20–40 μm modal diameter) characteristic of shelf sediments at the canyon head. Most of the suspensate delivered to the canyon is derived from the intermediate nepheloid layer (INL) over the slope, which in turn originates from the bottom nepheloid layer (BNL) on the shelf. Current meter data and particle sizes suggest that sediment accumulating in the upper head of the canyon ( 1000 m depth) is apparently resuspended from the outer shelf south of the canyon. Transport is dominantly across-canyon (rather than offshore) in a north-northwesterly direction. Storms strongly influence sediment transport, dramatically increasing suspensate modal sizes in the uppermost portions of the canyon head ( 30 μ m particles restricts sand and coarse silt accumulation primarily to the southern portion of the upper canyon head.