Gulf of Mexico Natural Oil Seeps: Microbes Thriving Above

Phytoplankton, the microbes that make the foundation of the marine life food chain, are healthy in Gulf of Mexico water where oil and gas bubbles are flowing up from natural seeps on the seafloor, according to a new study.

While the oil doesn't appear to have a direct relationship of helping the microbes, it isn't killing them when it occurs in such a low concentration. Also, as the rising bubbles create turbulence, they drag up helpful nutrients from deep below. As a result, phytoplankton above the oil seeps are present in nearly twice the number of those a few scant kilometers away.

"This is the beginning of evidence that some microbes in the Gulf may be preconditioned to survive with oil, at least at lower concentrations," Ajit Subramaniam at Columbia University and co-author of the study, said in a release. "In this case, we clearly see these phytoplankton are not negatively affected at low concentrations of oil, and there is an accompanying process that helps them thrive. This does not mean that exposure to oil at all concentrations for prolonged lengths of time is good for phytoplankton."

This is the first study to show this type of interrelation among the sea floor, subsea floor and processes among microbes near the ocean surface, Andy Juhl, co-author, said in the release.

Both researchers and other colleagues involved in the Ecosystem Impacts of Oil and Gas Inputs to the Gulf (ECOGIG) consortium have been looking into oil seep interactions since shortly after the Deepwater Horizon spill in 2010. They aim to find ways to better respond to such disasters and to learn how oil interacts with the ocean during catastrophic releases.

In comparison with an oil-well catastrophe, natural seeps are very small. Such a seep can produce a slick that is on the surface for one to seven days and covers between 1 and 100 square kilometers. That compares with the Deepwater Horizon well having stretched over about 11,200 square kilometers and endured for months, Subramaniam noted in the release. However, seeps can release enough gas and oil that researchers can smell it at the water surface and come across bursting oil bubbles.

Researchers are still learning which types of phytoplankton interact positively with small amounts of oil from natural seeps. They will also learn more through further mapping: "Satellite radar data have given us a detailed picture of where natural seeps are concentrated across deep seafloor of the Gulf of Mexico," co-author Ian MacDonald at Florida State University said in the release. "Building on this, the present, novel results show biological effects near the ocean surface in areas where seeps are most prolific."

The findings were recently published in the journal Nature Geoscience. 

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