Grantee Research Project Results
Biogeochemical Approach to Understanding Gas Hydrate Formation and Decomposition in the Gulf of MexicoEPA Grant Number: U916134
Title: Biogeochemical Approach to Understanding Gas Hydrate Formation and Decomposition in the Gulf of Mexico
Investigators: Lapham, Laura L.
Institution: University of North Carolina at Chapel Hill
EPA Project Officer: Cobbs-Green, Gladys M.
Project Period: January 1, 2003 through January 1, 2006
Project Amount: $149,268
RFA: STAR Graduate Fellowships (2003)
Research Category: Fellowship - Oceanography , Academic Fellowships , Aquatic Ecosystems
The objective of the research project is to determine whether gas hydrates are forming or dissociating at several hydrate-containing sites and which geochemical processes affect them. Gas hydrates are icelike solids that form in the presence of saturated methane concentrations under high pressures and low temperatures that are found in continental shelf sediments and permafrost. They are composed of rigid cages of water that enclose molecules of low molecular weight hydrocarbons, principally methane, along with carbon dioxide or hydrogen sulfide. The methane gas is produced by anaerobic bacteria or by the thermal breakdown of organic matter in deeply buried sediments. The global hydrate reservoir may contain around 1016 kg of methane carbon, about twice the amount of carbon stored in fossil fuels (Kvenvolden, 1988). If this estimate is correct, hydrates could represent the largest source of hydrocarbons on Earth and an important potential energy resource. It is, therefore, important to understand the actual processes controlling gas hydrate formation and dissociation under current sea floor conditions.Approach:
The first approach is to determine the gross dissolution rate of the hydrates. This will be completed by measuring the net gas flux out of hydrate-associated sediments and by measuring the biogeochemical processes such as sulfate reduction and methane oxidation occurring in the sediments. The second approach will be to determine directly the local formation or decomposition of the hydrates by measuring the in situ concentrations of major ions dissolved in porewaters near hydrates. By combining these two approaches, the formation and decomposition of hydrates can be fully understood. Quantification of net gas flux out of the surrounding sediments and consumption reactions via biogeochemical processes occurring in the sediments can provide key information about hydrate formation and decomposition. Previous studies at these sites demonstrate that the net flux of methane from dissociating hydrates is directly controlled by oxidative losses to anaerobic bacteria and chemosynthetic communities in surrounding sediments. Despite evidence that surrounding communities play key roles in oxidizing methane, investigations into the rates and mechanisms of the biogeochemical processes, such as sulfate reduction and methane oxidation, are sparse. Knowledge of these rates and how they influence local methane concentrations in the sediments is crucial to understanding formation and decomposition of the hydrates.Supplemental Keywords:
fellowship, gas hydrates, methane, hydrocarbons, anaerobic bacteria, chemosynthetic, Gulf of Mexico, sediments, sulfate reduction, methane oxidation, biogeochemical process, oxidative loss, dissociation, organic matter.