MacDONALD, I. R., and N. L. GUINASSO, JR., Geochemical and Environmental Research Group, Texas A&M University, College Station, TX, and C. P. GIAMMONA* and R. ENGELHARDT, Marine Spill Response Corporation, Washington, DC

ABSTRACT: Remote Sensing Natural Oil Seepage in the Gulf of Mexico

Natural oil seepage in the Gulf of Mexico causes surface slicks that are visible from space. A photograph of the sun-glint pattern offshore Louisiana taken from the Space Shuttle Atlantis on May 5, 1989, shows at least 124 slicks. A thematic mapper (TM) image

collected by the Landsat orbiter on July 31, 1991, shows at least 66 slicks. The natural origin of these slicks was documented by samples and descriptions made from a surface ship, an aircraft, and a submarine. The shape and frequency of the slicks argue against anthropogenic sources for the oil.

We derived a mathematical model that simulates formation of slicks based on a parameterization of sea-floor flow rate, downstream movement on the surface, half-life of floating oil, and threshold thickness for visibility We fit the model to the lengths and areas of slicks observed in the imagery and to a wind-drift rate of 20 cm/s; we specified a half-life of 48 h and a threshold thickness of 0.01 micrometer for the floating oil. We summed the individual seepage rates over the entire imaged area, and we extrapolated the rates over 1 yr. This exercise predicts that the slicks in the Atlantis photograph and the TM image represent total seepage of 426,000 bbl/yr and 120,000 bbl/yr, respectively.

The Gulf of Mexico seeps also offer a natural laboratory for studying the phenomenology of oil slicks and for testing oil-spill response procedures. We discuss some possible endeavors that could use this resource.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.