Observations of sediment flux to the Eel continental slope, northern California

Abstract

Sediment flux on the northern California slope off the Eel River was observed using time-series sediment traps between September 1995 and January 1997. A mooring that held three sediment traps (at 60, 220 and 435 m) and three current meters/transmissometers was placed in 450 m water depth. Thirty-three sampling periods of 10–16 days in length covered 394 days. All samples were analyzed for total mass, calcium carbonate, combustible matter and biogenic silica, and from these, lithogenic fluxes were determined. Total sediment-trap fluxes ranged from 0.1 to 24.2 g m −2 d −1, and annually averaged 1.1, 4.5 and 11.8 g m −2 d −1 at the top, middle and bottom traps, respectively. Lithogenic fluxes were 53, 70 and 83% at the top, middle and bottom traps. The middle trap experienced the greatest absolute variability as a result of intermediate-nepheloid-layer activity; 6 of the 33 intervals accounted for more than 50% of the flux. River, wind, wave, current, transmissometer and satellite data reveal that the magnitude of sediment flux was controlled by a variable mix of shelf sediment resuspension, river discharge, and margin circulation.