Quarterdeck 4.1
Countercurrents
Ocean weather
In a widely publicized news release, Shell, Amoco, Mobil and Texaco recently
announced that they will drill an exploratory well in Alaminos Canyon, located
on the outer continental shelf of the Gulf of Mexico about 200 miles southeast
of Corpus Christi, Texas. The plans are remarkable because the water depth
at the canyon site is 2324 meters (7,625 feet), a new record for subsea
oil and gas drilling and much deeper than current production wells.
Alaminos Canyon has long been of interest to oceanographers at Texas A&M.
The canyon is a deep depression defined by the edges of two lobate salt
canopies (see "Seismic stratigraphy and salt tectonics of the Alaminos
Canyon area" by Suzanne Hewitt in the Spring 1995 Quarterdeck). Similar
salt deposits cover large areas of the continental shelf off Texas and Louisiana.
The salt canopies frustrate conventional subbottom seismic methods and confound
the search for sub-salt petroleum deposits. Salt-free regions such as Alaminos
Canyon provide relatively transparent windows through which the subbottom
geologic features can be mapped. Recent seismic glimpses through the windows
on the Texas shelf hint at a potentially vast petroleum reservoir that could
rival the Alaskan North Slope in magnitude.
This issue's Cruise News article describes a new instrument that follows
the terrain of the seafloor as it records subbottom profiles and side-scan
images. A recent pilot cruise with this instrument on the R/V Gyre provided
unprecedented detail about the highly faulted structure of the seafloor
of Pigmy Basin, an intralobal depression on the outer Texas shelf. An upcoming
cruise in Alaminos Canyon likely will provide an exciting view of the subbottom
structures near the site of the exploratory well. These cruises are part
of a cooperative effort by scientists and engineers at the Offshore Technology
Research Center and oceano-graphers and graduate students, all at Texas
A&M.
The Alaminos site is located in the eddy "graveyard" of the northwestern
Gulf of Mexico, which further adds to its oceanographic interest. In this
region eddies pinched off from the Loop Current in the eastern gulf drift
slowly westward and eventually decay by interacting with the continental
slope. The eddies, typically 250 kilometers in diameter and 2000 meters
deep, may have current speeds of one meter per second (about two knots)
or greater near the surface. Strong currents can reach the bottom near the
outer shelf edge and persist for weeks in the Alaminos Canyon area, presenting
an engineering challenge and a potential safety hazard to drilling operations.
Thus it is important and perhaps crucial to deep exploration and eventual
production in the northwestern gulf to keep track of Loop Current eddies.
We need a predictive capability to forecast eddy tracks and decay products,
much like meteorologists track atmospheric cyclones and predict their local
influences. Ideally, slow-motion "ocean weather" forecasts for
the entire Texas shelf could be developed, using sophisticated computer
models and current oceanographic and atmospheric data. Taking our cue from
the Weather Channel, perhaps the television evening news programs should
include a colorful Ocean Weather Update, interpreted by a nattily dressed
oceano-grapher and accompanied by a soothing sound track. It might do wonders
for our public image.
--David A. Brooks
Editor
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Oceanography, Texas A&M University
rshatto@ocean.tamu.edu
URL=http://oceanography.tamu.edu/Quarterdeck/QD4.1/editorial.html
Updated May 27, 1996