How Low Can Life Go?

/ Source: Discovery Channel

There is a thriving realm of mysterious microbes of potential importance to the global carbon budget hidden beneath the sea floor near where the Earth's crust is being pulled apart, according to new evidence from deep-sea explorers.

In the frigid depths of the Juan de Fuca tectonic plate off the coast of the Pacific Northwest, warm water moving through the sea floor near the plate edges has been found loaded with dissolved organic matter with a telltale carbon signature that could have only come from microbes in the rocks.

The warm waters were captured as they poured from an old bore-hole and into the freezing waters, and were double-checked for contamination by comparing them to waters obtained from sterile, specially made samplers that were driven into the sea floor.

"It looks like a massive fire hose," said Matthew McCarthy of the University of California at Santa Cruz, referring to the pressurized, 80-degree Fahrenheit groundwater spewing from the old hole in the sea bottom. McCarthy is one of the authors of a paper about the secrets of that groundwater, being published in the January issue of the journal Nature Geoscience.

The goal of the work, McCarthy explained, was to irrefutably show that the waters from the hole were representative of what lies much deeper, rather than just contaminated by the human activities that drilled the hole.

"If there was ever any contamination, it was long gone," McCarthy said of he and his colleagues conclusions.

Indeed, now the researchers have evidence of what is probably a vast volume of lava rocks going down to unknown depths which are loaded with microbes. Those microbes make their living by using reactions on the surface of basalt rocks that have been erupted over the millennia on the seafloor.

The microbes belong to a group called called chemo-litho-autotrophs that live without any connection to the more common Earth ecosystems which are dependent on sunlight.

Such microbial ecosystems could be widespread in the oceans. If they are, they could play an important and unknown role in the cycling of carbon in the deep seas, said McCarthy.

"If these kinds of reactions are happening at Juan de Fuca, chances they are happening at other places are very high," agreed researcher Katrina Edwards of the University of Southern California. "The potential is pretty widespread."

So far the actual identities of the microbes is unknown, said McCarthy. "Our data don't tell you about the microbes that made it," he said.

Although some microbes have been found, it's not clear they are the source of the dissolved organic carbon in the water.

As for how it fits into the Earth's carbon budget, that's still unknown, says Edwards. She likes to visualize the carbon budget as being made of many carbon cycles that are like gears of different sizes and turning at different speeds.

"This one is moving slowly and we don't know how big it is," she said of the deep sea, chemo-litho-autotroph carbon cycle.

One thing that will help to begin defining its size will be more work on other seafloor spreading centers. Edwards and her team are planning just that, with a new observatory slated to be installed on the Mid-Atlantic Ridge in late 2011.