Characterization of modern off-shelf sediment export on the Eel margin, northern California

The processes that allow sediment to escape continental-shelf environments and be transported to the slope are investigated on the Eel margin. Previous results in this area reveal that a significant fraction of fluvial sediment discharged to the margin from the Eel River may be lost seaward of the shelf break. To address this issue, the styles of sediment escape are compared and contrasted between two slope environments: open slope (i.e., the bathymetrically smooth area) and submarine canyon (i.e., Eel Canyon).; Cores from the upper canyon show that sediment from the Eel River is quickly (<60 d) deposited to the seabed following a period of flooding. Sediment is deposited in the canyon every winter (during storms and floods), and appears to be transported by both sediment gravity flows and nepheloid layers. Sediment reaching the canyon is focused in the canyon thalwegs (evidenced by thicker deposits), which may be a consequence of periodic sediment gravity flows. A seasonal sediment budget indicates that the canyon is sequestering ∼12% of the Eel River discharge.; Long cores from the canyon reveal preserved seasonal deposits in the decadal sediment record. Over a 100-yr timescale, accumulation rates are high throughout the upper canyon (>1 mm/y), with the highest rates observed in thalwegs (up to ∼60 mm/y). The 100-yr sediment budget indicates that >2% of the Eel River discharge is accumulating in the upper canyon. However, this value drastically underestimates the total amount of sediment moving though the canyon, because an accurate calculation of accumulation rates is limited by core length, and sediment removed from the study area by slope failure is not included in this calculation.; Simultaneous measurements of sediment transport on the shelf, open slope and canyon indicate that wave resuspension on the shelf (producing elevated SSC), and favorable hydrographic conditions (currents and density structure) are necessary for sediment to escape seaward of the shelf break. Fluvial input does not appear to be the primary driving force behind sediment escape. Sediment is transported via intermediate and bottom nepheloid layers in both slope environments, which is controlled by a combination of wind- and tidally-driven processes.