|Methane gas in Gulf oil spill|
After a violent methane discharge severed the Deepwater Horizon rig from its well, oil and gas began spilling into the deep Gulf of Mexico at depths of ca. 1.5 km. Analyses of the leaking material by BP suggest a methane content of 40-50% by weight. Estimates of the leakage rate range from 5,000 to 70,000 barrels per day, thus given this methane content indicates that between 2 – 100 × 10^6 moles of CH4 are released per day from this disaster. Since an intentional methane release of this magnitude for research purposes would obviously never be allowed, this massive fossil methane discharge presents a very unique opportunity for us to investigate two different hypotheses on how the natural oceanic methane system functions and contributes to both climate and dissolved oxygen concentrations.
HYPOTHESIS 1: Significant and quantifiable amounts of methane released rapidly from naturally decomposing oceanic clathrate hydrates will be both dissolved in the water column and emitted to the atmosphere. While Hypothesis 1 may seem overly simple, geochemical data indicate that significant clathrate decomposition has occurred in the geological past, but it is unknown if this methane (a very potent greenhouse gas) entered the atmosphere to contribute to climate change or is retained in the ocean. This deepwater anthropogenic leakage simulates a natural rapidly decomposing clathrate hydrate, enabling us not only to answer Hypothesis 1, but also to quantify the absolute and relative fluxes entering both the water column and atmosphere.
HYPOTHESIS 2: The oxidation and ebullition of methane in the water column will significantly contribute to the low oxygen zones in the northern Gulf of Mexico. The Gulf of Mexico has extensive shallow and deepwater natural methane and oil seeps but the effect of this methane on dissolved oxygen levels has never been investigated; this anthropogenic disaster highlights the potentially significant linkage between CH4 and O2 cycling in the Gulf of Mexico. Without considering ebullition effects, our preliminary calculations indicate that a 10% reduction of dissolved oxygen can be achieved in the low oxygen zones of the Gulf of Mexico in 4 – 190 days at these estimated methane fluxes.
For more information - see additional story on Methane Cruise.