Huge amounts of gases like methane and pentane spewed forth from the BP’s Deepwater Horizon oil well blowout along with the approximately 206 million gallons of crude oil.
Publishing yesterday in the journal Nature Geoscience, University of Georgia oceanographers estimated that 500,000 tons of gaseous hydrocarbons escaped during the spill. They calculated that the gas leak was the equivalent to a minimum of 1.6-1.9 million barrels of oil, but could be as high as or 2.2-3.1 million barrels of oil.
The wide range of estimates reflects the many uncertainties involved, but even the lowest figure adds significantly to the estimated amount of hydrocarbons released by the well.
“These calculations increase the accepted government estimates by about one third,” said co-author Ian MacDonald of Florida State University in a University of Georgia press release.
“Deepwater Horizon underscored how ill-prepared the nation is to respond to future accidents. As a nation, we need to hear this deep-sea Sputnik wake-up call,” said co-author Ira Leifer of the University of California-Santa Barbara.
Because the release occurred under nearly one mile of water, the pressure and cold temperature kept the gas from escaping to the surface. Instead it formed ice-like flakes of gas hydrates.
The gas and oil provided a rich source of food for undersea bacteria. As those bacteria ate the oil and gas, their respiration sucked the oxygen out of the water.
The huge amount of hydrocarbons involved means that the bacteria population had an ample supply of food. The bacteria may have been limited by the amount of other nutrients, like nitrogen and iron, available on the floor of the Gulf of Mexico, but the effects may be long lasting.
“We’re not talking about extensive hypoxic [oxygen-deprived] areas offshore in the Gulf of Mexico,” said lead author Samantha Joye of the University of Georgia.
“But the microbial oxidation of the methane and other alkanes will remove oxygen from the system for quite a while because the time-scale for the replenishment of oxygen at that depth is many decades,” explained Joye.
The long term effects of disasters like the BP spill are still unknown and will require long-term observation.
“This study highlights the value of knowledge gained from deep sea hydrate seepage research but also how poorly deep sea processes are understood, such as the role methane hydrates played in forming the deep methane plumes documented by this study,” Leifer said.
IMAGE 1: BP’s Deepwater Horizon oil spill seen from space May 24, 2010 (NASA, Wikimedia Commons)