Rare Carbon Dioxide "Lake" Found Under the Ocean, Scientists Report
Richard A. Lovett
for National Geographic News
|August 30, 2006|
A team of scientists based in Japan and Germany has found an unusual
"lake" of liquid carbon dioxide beneath the ocean floor.
On Earth's surface carbon dioxide (CO2) is normally a gas, but in the cold, high-pressure ocean depths it cools and becomes a liquid.
Because CO2 in the atmosphere plays a major role in global warming, some scientists have suggested disposing of the gas by injecting it deep beneath the seabed, where it could be stored in liquid form.
The newly found CO2 lake, a rare natural formation, could offer clues to whether such a plan might work and how it might affect undersea ecosystems.
Fumio Inagaki of the Japan Agency for Marine-Earth Science and Technology in Yokosuka and colleagues report their find today in the online early edition of Proceedings of the National Academy of Sciences (PNAS).
Inagaki's team found the lake while studying hydrothermal ventsundersea volcanic hot spotsin the East China Sea off the coast of Taiwan (map of Taiwan).
The lake's presence was unexpected, because the seamount lies only 4,600 feet (1400 meters) below sea level. At that depth, liquid CO2 is lighter than water and will slowly rise, eventually bubbling into the air as gas.
Normally liquid CO2 has to be at a depth of 10,000 feet (3,000 meters) for it to be dense enough not to rise.
In this case, Inagaki's team says, CO2 has been moving upward from a deep magma chamber.
As it nears the seabed, the CO2 encounters cold water in the top layer of sediment. It reacts with this water to form a type of ice called a carbon dioxide hydrate.
The hydrate creates a cap in the sediment that traps additional liquid CO2 beneath it.
The lake's existence seems to confirm a study published in PNAS earlier this month by Kurt Zenz House, a graduate student at Harvard University in Cambridge, Massachusetts.
In that study House postulates that a hydrate cap could be created deliberately as a way to sequester CO2 beneath the seas.
"It's an interesting paper," House says of the latest find.
Kenneth Nealson, a geobiologist at the University of Southern California in Los Angeles, agrees.
In a soon-to-be-published commentary, Nealson notes that while liquid CO2 has been found at other undersea volcanoes, few had expected it to accumulate in the manner seen by Inagaki's team.
"How many such lakes are there?" he writes. "How stable are they, and are they potential players in the global carbon cycle?"
Inagaki's team also looked at the impact of the lake on microbes living in its vicinity.
They found high numbers of bacteria above the hydrate cap, but only one percent as many adjacent to the liquid CO2 layer.
"That suggests that the presence of the liquid carbon dioxide is having a negative effect on the microbial communities," House said. "They still exist, but are much more sparse."
That's important to know, he adds, because if humans seriously attempt to dispose of large amounts of CO2 in the seafloor, it will create much larger artificial lakes.
Study co-author Inagaki adds that it's startling that any microbes exist within the liquid CO2 layer.
They probably survive in "microhabitats" within the complex mixture of carbon dioxide, hydrates, and seawater found in the sediments, he says.
"If we can find a similar environmental setting at the subsurface of polar Mars we may find a similar habitat for life," he said by email.
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