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Fieldwork

Research Vessel Marion Dufresne Cores Tampa Bay, Florida


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The first core recovered 11.5 m of sediment
Tampa Bay sediments: The first core recovered 11.5 m of sediment.
When the research vessel Marion Dufresne, France's huge coring vessel, finished coring in the Gulf of Mexico, Terry Edgar (U.S. Geological Survey [USGS], St. Petersburg, FL) and Deb Willard and Tom Cronin (USGS, Reston, VA) arranged to have the ship take as many as three cores in the deepest natural depression in Tampa Bay before it docked in the Port of Tampa.

Seismic data acquired by the University of South Florida indicate that about 16 to 17 m of sediment overlies the deepest recorded reflection in this depression. Water depth at the chosen sites is about 9 m, which gave the ship just 3 m of clearance between the hull and the bay floor. The captain of the Marion Dufresne agreed to core in just about the shallowest water depth ever attempted from this ship. (The shallowest core is believed to be from 8-m water depth in Chesapeake Bay.)

the trigger arm had to be held down by hand until the core was deployed
Above: Water depth was less than the length of the trigger line, and so the trigger arm had to be held down by hand until the core was deployed.
Below: The last core recovered only 4.5 m of sediment and came up looking like a banana, as bent core pipes are called.

the last core recovered only 4.5 m of sediment and came up looking like a banana
Terry, Deb, and Chris Reich (USGS, St. Petersburg, FL) and Gregg Brooks, Bekka Larson, and Dave Hastings (Eckerd College, St. Petersburg, FL) joined the Marion Dufresne before dawn on July 18. Ben Flower (University of South Florida) participated with the deep Gulf of Mexico team, as well as with our Tampa Bay project team.

Owing to the shallow water depth, the trigger arm on the corer had to be held by hand, because the trigger weight was already on the bottom of the bay before the core barrel was released. In fact, the core barrel was already in the bottom before the core was deployed.

The first core recovered 11.5 m of sediment that included marine sediment at the top, freshwater sediment in the middle, and marine sediment at the bottom of the core, suggesting that the oldest marine sediment is at least as old as the latest interglacial (stage 5, approx. 125 ka).

The second core parted at a weld, and we were left with about 6.5 m of pipe sticking out of the bottom, which Chris Reich, Keith Ludwig, Rich Young, and Terry Edgar located, identified, described, and tagged the following day, July 19. Terry Kelley, Rich Young, and some commercial divers removed the pipe with a cutting torch on July 20. No sediment was recovered.

The third core bent and recovered only 4.5 m of sediment, but it was from this core that Bekka Larson (Eckerd College) pulled a gastropod out of black mud in the core catcher. When we opened the cores, it was clear that this core stopped in the nonmarine section, whereas the first core had penetrated the entire freshwater sequence and terminated in the underlying marine sediment.


Related Sound Waves Stories
Gas Hydrate Studied in the Northern Gulf of Mexico
September 2002
Marion Dufresne Coring in Chesapeake Bay
August 1999

Related Web Sites
Tampa Bay Pilot Study
U.S. Geological Survey (USGS)
Marine Science Program
Eckerd College
College of Marine Science
University of South Florida

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in this issue: Fieldwork cover story:
Gulf of Mexico Gas Hydrate

Tampa Bay Coring

North Carolina Coastal Erosion

Endangered White Abalone

Marbled Murrelets

Research Sediment Core Drilling Proposal

African Dust Microbiology

Outreach Tall Ships

Gulf of Mexico Teacher Workshop

Coastal Louisiana Interview

MRIB Makes Headlines

Meetings U.S. Commission on Ocean Policy

Numerical-Modeling Workshop

Staff & Center News WHFC Employees Farewell

Sound Waves Staff

Publications September Publications List


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