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Sediment Sampling Off Southern California

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preparing a vibracore
Brian Edwards (left) and Jon Kolak prepare a vibracore for deployment.
Once again, the Western Region Marine Facility staff pulled off a miracle by converting an Alaskan crabber, the M/V Ocean Olympic, into a fully outfitted oceanographic research vessel for the month of June. The ship departed Redwood City on June 4 and initially conducted multichannel and Huntec profiling and marine mammal observations in support of the Southern California seismic hazards project under the direction of Bill Normark (see article "Southern California Earthquake Hazards"). Bill transferred the ship to us (Brian Edwards and Homa Lee) in San Diego on June 17. Our goal was to move as much bottom sediment onto the ship as we could over the next two weeks. Our coring operations had a variety of purposes and extended all the way from near San Diego to the northern edge of Monterey Bay.

The first two days of our cruise (O2-99-SC) were dedicated to taking piston cores at locations that had been pre-selected by Bill Normark. Bill's goal was to sample sedimentary reflections that could be identified in the Huntec lines and subsequently dated. This chronologic information could then be used to estimate most recent movement on observed faults. In all, 12 piston cores were taken ranging in length up to 4 m. The cores and all sediment samples taken on our cruises were logged for density, sound velocity, and magnetic susceptibility using our multi-sensor logger.

The next five days of O2-99-SC were committed to the Los Angeles Shelf Pollution and Waste Disposal Project. The goals of this project are to understand the sedimentology and oceanography of Santa Monica Bay, one of the most human-impacted offshore areas on the West Coast, and to use this understanding to forecast the fate of contaminated sediment.

We used this opportunity in our last sampling year to obtain cores for a broad variety of purposes. In all, we acquired 20 piston cores, 15 vibracores, 31 box cores, 6 grab samples, and one very smelly Kasten core from a "sludge" deposit. We will be dating the piston, box, and vibracore samples using Pb210 and C14 techniques to develop a better understanding of sedimentation conditions in Santa Monica Bay during the late Holocene, with special emphasis on the last 100 years. Chris Sommerfield, a USGS post-doc at Woods Hole, is focusing on the last few thousand years, and Clark Alexander, as part of a co-op with the Skidaway Institute of Oceanography, is considering the last 100 years. A bottom photograph was taken with each box core using Hank Chezar's camera system. A representative of the City of Los Angeles Department of Sanitation participated in one day of the cruise, sampling box cores for living things.

sub-sampling a boxcore
Sub-sampling a boxcore. From left to right: Kathy Presto, Jon Kolak, and Brian Edwards.
Jon Kolak, a USGS post-doc in Menlo Park, sampled some stations as part of a study of hydrocarbons in sediment. The grab samples were taken for Pete Dartnell, who is working to use acoustic backscatter measurements as a measure of habitat. Five cores were taken for the Southern California Coastal Water Research Project (a group of public agencies) to be analyzed for pesticides and metals. Our sampling work in Santa Monica Bay was hugely successful, and we now have adequate sample resources to complete our study.

On June 25 we picked up a group of Monterey Bay Aquarium Research Institute (MBARI) scientists in Port Hueneme and began a five-day piston-coring venture. The MBARI team included Gary Greene and Norman Maher (formerly USGS) and was led by MBARI's newest scientist, Charlie Paull. We took 25 piston cores for MBARI in three different environments: a heavily pockmarked area off Big Sur, a feature identified as "Smooth Ridge" in western Monterey Bay, and the head of Monterey Canyon. We experienced the worst sea conditions of our cruises during this time but lost only about one day of work. The remainder of the time was very successful, providing plenty of samples to use in collaborative studies of sedimentology and geochemistry.

The last day was spent in Monterey Bay taking 8 box cores for Jon Kolak. Roger Lewis will be using Pb210 methods to determine accumulation rates, and Jon will be looking at geochemical tracers to estimate the original source of the sediment. On July 1, we sailed through the Golden Gate and returned to our Marine Facility in Redwood City. The conversion of the Ocean Olympic was quickly reversed and an Alaskan crabber again came to life. All of us were very pleased with this mode of operation and were particularly happy with the cooperation we received from the ship's crew. We are all missing the cook's food and trying to lose weight!

Related Web Sites
Los Angeles Shelf Pollution and Waste Disposal Project
U.S. Geological Survey (USGS)
Monterey Bay Aquarium Research Institute (MBARI)
non-profit research center

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