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Gas and Oil Seepage and Hydrothermal Venting in the Ocean Bottom
— Detection by Fluorescence

Jean K. Whelan, Nathan Mah, and Greg Eischeid, Departement of Marine Chemistry & Geochemistry, Woods Hole Oceanographic Institution, Woods Hole MA 02543

Robert Chen and Xuchen Wang, Department of Environmental Sciences, University of Massachusetts, Boston, MA 02125

Harry Roberts and Paul Aharon, Center for Coastal Studies & Department of Geology & Geophysics, Louisiana State University, Baton Rouge, LA 70803


An abundance of evidence suggests continuous or episodic upward movement of fluids from deeper sediments into surface sediments and ocean bottom waters (Table 1). These seepages may have been volumetrically underestimated in the past, both in oil and gas productive areas and in tectonic regimes (e.g. hydrothermal vent areas) because they often occur through small seemingly unimportant localized cracks in the seafloor . However, even if these venting features are small, the volume of expelled fluid can be important: even a small fracture can deliver orders of magnitude more fluid than ordinary compaction and diffusion processes. Here we present initial results on successful deployment of CTD fluorescence for continuous detection of bottom venting fluids both in a known oil and gas seep area (Green Canyon in the offshore Louisiana Gulf of Mexico, Figure 1a ) and in a hydrothermal vent area (Guaymas Basin, Gulf of California, Figure 1c ). Our initial results confirm the very localized and possibly episodic nature of these venting features which would not have been detected without a continuous localized detection technique.

Figures and Tables

Figure 1: Locations of initial bottom CTD fluorescence measurements:
a) overview of location of Gulf Coast Green Canyon area;
b) close-up: location of Green Canyon manned submersible dive sites;
c) overview of location of Gulf of California Guaymas Basin hydrothermal venting area;
d) close-up: Guaymas Basin, location of Jason (unmanned submersible) cruise track

Figure 2: Green Canyon: CTD fluorescence data, Seatech DOC fluorometer.

Figure 3: Green Canyon: DOC

Figure 4: Green Canyon: laboratory quantitative fluorescence data calibrated to Quinine standard

Figure 5: Green Canyon - excitation-emission fluorescence spectra:
a ) water and hexane extracts of unaltered oil;
b ) bottom water from Dive Site 2893;
c ) bottom water from Dive Site 2900;
d ) bottom water from Dive Site 2901;
e ) typical open ocean mid-water away from seepage site.

Figure 6: Green Canyon water, GCMS total ion chromatogram (TIC) of methylene chloride extract in comparison to tetracosane recovery standard.

Figure 7: Guaymas Basin: CTD fluorescence data, Seatech (DOC) and Chelsea (aromatic hydrocarbon) fluorometers - overall.

Figure 8: Guaymas Basin comparative fluorometer measurements (dive of 4/20/98).

Table 1: Summary observations suggesting seepage to bottom sediments may have been underestimated in past


Captain and crew of Edwin Link and Johnson Sea Link; Dana Yoerger and the Deep Submergence Group for "piggybacking" us on their Guaymas Jason dive; Al Bradley and Ellen Druffel for helpful discussions which got us to thinking about this work. Financial support from the Vetlesen Foundation through a grant to the Woods Hole Oceanographic Foundation and from the Department of Energy (grant no. DE-FG02-86ER13466 to Jean Whelan) is gratefully acknowledged.

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