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Fieldwork

Successful Deployment of Tripods and Moorings Off Southern California, Or "Ten Fingers, Ten Toes, and a Clear Deck at the End of the Day . . ."


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a diver works the coral drilling rig
Tripods: USGS tripods await deployment on the deck of the R/V R.G. Sproul.
Working aboard the R/V R.G. Sproul between June 12th and June 15th, Coastal and Marine Geology scientists from Menlo Park and Woods Hole successfully deployed an array of tripods and moorings in San Pedro Bay off Huntington Beach in Southern California. Menlo personnel included Joanne Thede Ferreira, Dave Gonzales, Marlene Noble, Kevin O'Toole, Hal Williams, and Jingping Xu. Woods Hole personnel included Jonathan Borden, Rick Rendigs, and AndreŽ Ramsey.

Huntington Beach is a very popular swimming and surfing area that has been closed sporadically during the past several summers because of bacterial contamination. Last month's deployment is part of a comprehensive study designed by CMG scientists to determine pathways in the coastal ocean that could carry contaminated material to Huntington Beach. The study is being conducted in cooperation with the Naval Postgraduate School, Scripps Institute of Oceanography, Science Applications International Corporation (SAIC), University of Southern California, and University of California Irvine. One of many suspects for the contaminant source is a sewage outfall that discharges treated effluent 5 mi seaward from Huntington Beach. The outfall is located in a very complex section of the continental shelf, near the shelf break and adjacent to a prominent submarine canyon.

shaded mulitbeam bathymetry map of the continental shelf off Los Angeles
Symbols used on the map above to denote the location of the SCRIPPS array, USGS moorings, other moorings, and power plant outfall. The area of the image is approximately 20 kilometers by 20 kilometers. Offshore Los Angeles: Mooring locations shown on multibeam bathymetry of continental shelf and slope off Newport Beach and Huntington Beach, Greater Los Angeles area. Yellow lines above the shelf break are 5-m contour intervals from 10 m to 100 m water depth; blue lines below the shelf break are 20-m contour intervals from 120 m to 400 m water depth. Diagonal red line is sewage outfall pipe. Black lines shoreward of outfall pipe represent lower course of Santa Ana River (on line with outfall pipe) and stormwater runoff channels.
The study partners will deploy an array of 13 moorings (see map) to investigate transport of water and suspended materials through the region. The USGS moorings were the first to be deployed, and they are the only moorings that include bottom tripods to determine how and when sediment re-suspension occurs. An array of four tripods, the Naval Postgraduate School's anti-trawl-cage-mounted ADCPs (Acoustic Doppler Current Profilers), four surface moorings and four sub-surface moorings occupy the five USGS sites. Colleagues from cooperating institutions will deploy moorings at the remaining sites in the next few weeks. The moorings will be out through mid-October (4 months).

The weather for last month's deployment was great, enabling us to set all the moorings on a single day with daylight to spare! The second day, we picked up the Naval Postgraduate School's meteorological buoy at Fish Harbor, deployed it, and spent the rest of the day taking grab samples across and along the shelf. A cursory look at sediments collected suggests that those at the shelf break are coarser than on the mid-shelf. The coarsest sediments seemed to be located along the shelf break adjacent to the submarine canyon. This distribution is reminiscent of grain-size dispersal on the adjacent Santa Monica Bay shelf (to the northwest). On the Santa Monica Bay shelf, energetic internal tides and internal waves at the shelf break contribute to re-suspension and advection of fine sediments. In October we may have the measurements to support similar sediment dynamics in San Pedro Bay.


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in this issue: Fieldwork cover story:
Mapping Puget Sound

Biscayne Nat'l Park

Glacier Bay Cruise

Tripod Deployment

Outreach GIS Group Teaches Science

Juneteenth Celebration

Meetings Geochemical Processes

Geologic Discipline EMAC

Wetlands Meeting

Awards Closing the Circle

Staff & Center News Eric Thompson

NAGT Summer Interns

Woods Hole Interns

Jerry Parker Memorial

Gaye Farris Re-Elected to STC Exec Board

Publications "Natural Gas Hydrates" Book

July Publications List


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