1995 Current and Sediment Study in Monterey Canyon

Monterey Canyon

Moorings were deployed for a year in Monterey Canyon across

• a narrow portion, moorings NA and NN (on map) (axis depth 1450 m)
• a wider part, moorings WN, WA and WS (on map) (axis depth 2837 m)
• where the canyon cuts across the fan (mooring F on map) (axis depth 3223 m)

Each mooring had current meters, transmissometers, and sediment traps.

The largest currents in the canyon were tides, which mainly flowed up and down the canyon. The largest current speeds were near the bed, and tides in the narrow portion of the canyon were four times larger than in wider sections.

An unusual 3-day oscillation was observed in the canyon for the entire deployment period. The oscillation had large spatial scales because it was seen simultaneously at all sites along the canyon axis, spanning a horizontal distance of 75 km and a vertical distance of 2000 m. We are currently investigating the cause of the oscillation.

A sediment trap was deployed 80 m above the bed in the narrow axis, large amounts of particles and other material settled into the trap: 22-60 grams per square meter per day. The trap overflowed after 3 months.

Subsequently, a very large turbidity event occurred that lasted more than a week. In 4 hours, the water column went from clear to very cloudy, the pressure changed, and the water became slightly warmer and fresher. We think this material either slumped off the canyon walls or came down the canyon as a turbidity current.

A few definitions:

• current meter - instrument that measures how fast and in which direction water is flowing
• transmissometer - instrument that measures water clarity. The water becomes progressively more cloudy as an increasing amount of material is suspended in the water column.
• turbidity event - a period of time when the water column becomes very cloudy. This means a lot of material is suspended in the water column.

Participating scientists and agencies:

• Marlene Noble, Western Coastal and Marine Geology of the U.S. Geological Survey
• Cindy Pilskaln, University of Massachusetts' School of Marine Sciences
• Leslie Rosenfeld, Naval Postgraduate School
• Frank Schwing, Pacific Fisheries Environmental Laboratory : Environmental Research Division of the National Oceanic and Atmospheric Administration's National Marine Fisheries Service, Southwest Fisheries Science Center

The study was jointly funded by the U.S. Geological Survey and Office of Naval Research.

Publications:

• Kinoshita, K. and M. Noble, 1995, The Monterey Submarine Canyon, California Moored Array Data Report, U.S. Geological Survey Open-file Report 95-838.
• Noble, M. A., K. Kinoshita, L. Rosenfeld, C. Pilskaln, F. Schwing and S. Eittreim, 1996, Currents and Sediment Movement in Monterey Canyon, Abstract and poster at the 6th Annual Monterey Bay Research Symposium, Sanctuary Currents '96, pg 29.
• Noble, M. A., C. H. Pilskaln, L. Rosenfeld, and F. Schwing, 1994, Currents and Sediment Movement in Monterey Submarine Canyon, abstract, Eastern Pacific Ocean Conference (EPOC), Timberline Lodge, Mt. Hood, Oregon, October 1994.

For additional information on this study, contact Marlene Noble