Fate and Effects of Barium and Radium-Rich Fluid Emissions from Hydrocarbon Seeps on the Benthic Habitats of the Gulf of Mexico Offshore Louisiana

The Minerals Management Service (MMS), Gulf of Mexico OCS Region, announces the availability of a new study report, Fate and Effects of Barium and Radium-Rich Fluid Emissions from Hydrocarbon Seeps on the Benthic Habitats of the Gulf of Mexico Offshore Louisiana.

The primary objectives of this study were to document products and processes related to naturally occurring barium and radium-rich fluid emissions from hydrocarbon seeps, and assess their impact on the offshore habitats in the deepwater Gulf of Mexico.

Formation-water-derived fluids emerging on the seafloor are anomalously enriched in radium (Ra) and barium (Ba) relative to seawater by factors of up to 4.5x10⁴ and 15x10⁴, respectively. Their migration time from the source to the seafloor is established to be < 20 years on the basis of the relatively short-lived ²²⁸Ra isotope content. Sulfur, oxygen, and strontium isotope compositions indicate that the Gulf of Mexico seep barite deposits formed by the mixing of sulfate-rich seawater with barium-, strontium-, and calcium-rich formation fluids seeping with gaseous hydrocarbons, primarily thermogenic methane. The chimneys are erected vertically above the seafloor whereas the crusts drape mud volcanoes and/or form pavements at the sediment/water interface. These results indicate that the Ba-Ra-rich fluid expulsion on the seafloor, triggering barite deposition, is a rapid and recent event. The uptake of Ba and Ra by the fauna inhabiting the barite-bearing seeps was found to be proportional to the Ba/Ra ratio in the pore fluids. Mussels harboring methanotrophic endosymbionts average 0.6 desintegration per minute per gram (dpm/g) and 0.5 dpm/g ²²⁶Ra for soft tissues and calcareous shells, respectively, which are significantly higher than those reported for shallow marine mussels. Vagrant, heterotrophic fauna living around the seeps yield ²²⁶Ra and Ba up to 10.7 dpm/g and 4,319 parts per million, (ppm) respectively. The considerably higher levels of Ra and Ba in the heterotrophs are probably acquired through ingestion of barite particles.

For more information about this study or the Environmental Studies Program in general, contact the Environmental Sciences Section (MS 5430), 1201 Elmwood Park Boulevard, New Orleans, Louisiana 70123-2394, telephone (504) 736-2752.

You can obtain copies of the report from the Minerals Management Service, Gulf of Mexico OCS Region, at a charge of $10.00 by referencing OCS Study MMS 2001-004. You will be able to obtain this report also from the National Technical Information Service in the near future. Here are the addresses. You may also inspect copies at selected Federal Depository Libraries.

Minerals Management Service
Gulf of Mexico OCS Region
Public Information Office (MS 5034)
1201 Elmwood Park Boulevard
New Orleans, Louisiana 70123-2394
Telephone requests may be placed at
(504) 736-2519, 1-800-200-GULF, or
FAX: (504) 736-2620

U.S. Department of Commerce
National Technical Information Service
5285 Port Royal Road
Springfield, Virginia 22161
(703) 487-4650 or FAX: (703) 321-8547
Rush Orders: 1-800-336-4700

The MMS, a bureau in the U.S. Department of the Interior, is the federal agency that manages the nation's natural gas, oil and other mineral resources on the outer continental shelf. The agency also collects, accounts for and disburses more than $5 billion per year in revenues from federal offshore mineral leases and from onshore mineral leases on federal and Indian lands.