for National Geographic News
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.
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