Along with tons of oil, the Deepwater leak also released massive amounts of hydrocarbon gasses like propane and ethane, which are slowly dissipating under the water. Far from "killing the oceans," these gasses are feeding huge bacterial colonies.
There are many kinds of bacteria that love to slurp up natural gasses, and the Deepwater spill is now home to huge bacterial blooms devoted to feasting on ethane and propane. Though this sounds like a great thing - our natural disaster is another species' boon - it could pose a problem for life forms in the ocean which depend on oxygen to breathe. (Most fish, for example, pull oxygen from the water via their gills.) In the process of eating ethane and propane, these bacteria also remove oxygen from the water. As geochemist David Valentine and colleagues wrote in Science yesterday, bacterial respiration (feeding) was responsible for 70% of the drop in ocean oxygen levels near the plumes:
From 11 to 21 June 2010, we investigated dissolved hydrocarbon gases at depth using chemical and isotopic surveys and on-site biodegradation studies. Propane and ethane were the primary drivers of microbial respiration, accounting for up to 70% of the observed oxygen depletion in fresh plumes. Propane and ethane trapped in the deep water may therefore promote rapid hydrocarbon respiration by low-diversity bacterial blooms, priming bacterial populations for degradation of other hydrocarbons in the aging plume.
In fact, bacterial respiration was the very first thing that cause oxygen levels to drop in the water. And more bacteria are flocking to the area. About half of the bacteria near the plumes were eating hydrocarbon gas, which means oxygen levels will continue to be affected. Eventually, Valentine and colleagues say, about two-thirds of the microbes in the Deepwater area will be living on natural gas.
The researchers determined this by sending down probes to analyze the locations of the natural gas plumes, which will dissipate long before they reach the surface of the ocean. Below, you can see the map they made of where the gas was. Then, they scooped up bacteria from the region and analyzed the microbes' DNA to determine what percentage of them were hydrocarbon-eaters.
It's worth noting that a reigning theory about why our atmosphere contains oxygen is that bacterial respiration produced the gas as a byproduct - thus poisoning the world for non-oxygen breathers and paving the way for life as we know it. Bacteria can have a profound effect on the biosphere. They gave us oxygen, and they could take it away.
Images via David Valentine.