January 17, 2011

Deepest Part of Ocean Acts As Carbon Sink

Science have probed the climate secrets of the Marianas Trench in the western Pacific Ocean.

The international team used a submersible, designed to withstand immense pressures, to study the bottom of the deepest part of the ocean.

The scientist early results reveal that ocean trenches are acting as carbon sinks.

This suggests that they play a larger role in regulating the Earth's chemistry and climate than what was previously thought.

Although explorers Jacques Piccard and Don Walsh reached the deepest part of the Marianas Trench in 1960, no human has been back since.

The scientific missions, including this recent visit to the Challenger Deep stop, have been carried out using unmanned underwater vehicles.

Lead researchers Professor Ronnie Glud, from the University of Southern Denmark and the Scottish Association for Marine Science (SAMS), told BBC that working at over 1,000 atmospheres of pressure was challenging, but advances in technology had made it possible.

He said, "This is the first time we have been able to set down sophisticated instruments at these depths to measure how much carbon is buried there."

Professor Glud worked with scientists from the Japan Agency for Marine Earth Science and Technology (JAMSTEC) and from the U.K. and Germany to explore the depth with a lander equipped with special sensors packed in a titanium cylinder that was able to resist the remarkable pressures.

The lander was launched from a ship and took three hours to free-fall to the sea bottom, where it carried out pre-programmed experiments before releasing its ballast and returning to the surface.

The tests helped the scientists assess the abundance of carbon at those depths.

Professor Glud told BBC: "Basically, we are interested in understanding how much organic material - that is all the material produced by algae or fish in the water above - settles at the sea bed, and is either eaten by bacteria and degraded or is buried."

"The ratio that is either degraded or buried is the ultimate process determining what are the oxygen and carbon dioxide concentrations of the oceans and the atmosphere, and this gives us an overall picture of how efficiently the sea can capture and sequester carbon in the global carbon cycle."

While this has been studied in other areas of the ocean, the role deep sea trenches play in the carbon cycle has until now remained largely unknown.

Professor Glud told BBC: "Although these trenches cover just 2% of the ocean, we thought they might be disproportionately important, because it was likely that they would accumulate much more carbon because they would act as a trap, with more organic matter drifting to the bottom of them than in other parts of the ocean."

He said that preliminary data from his experiments suggested that this was the case.

He said: "Our results very strongly suggest that the trenches do act as sediment traps. And they also had high activity, meaning that more carbon is turned over by bacteria in the trenches than is turned over at 6,000m of depth in the abyssal plain."

"What it means is that we have carbon storage going on in these trenches that is higher than we thought before, and this really means that we have a carbon dioxide sink in the deep ocean that wasn't recognized before."

The next stage for the team is to quantify their results and work out exactly how much more carbon is stored in deep sea trenches compared with other parts of the sea, and how much carbon is being carried out by what the bacteria turnover.

The researchers said that this should help them to better establish the role of the ocean trenches in regulating climate.

This is not the first time deep-sea trenches have surprised scientists.

The University of Aberdeen's Oceanlab team have revealed through recent studies that marine life is much more abundant in this hostile habitat than what was previously thought.

The team filmed the deepest living fish ever to be caught on camera in 2008, along with other animals likes amphipods that were present in large numbers even deeper.

Dr Alan Jamieson, from Oceanlab, told BBC the new study was helping researchers to build up a better idea of what happens in the deepest of the deep.

He said: "The trenches continue to amaze us."

"And to see an experiment such as this carried out at these extreme depths is a great leap forward in deep-sea science."

"These studies will greatly enhance our understanding of how the deep trenches contribute to carbon cycling in the world's oceans."


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