Icebergs help global warming

2007-06-22 15:30

Chicago - The icebergs of the Southern Ocean around Antarctica, far from being sterile chunks of floating ice, are "hotspots" of activity that may play a role in global warming, oceanologists said on Thursday.

Researchers who examined two mammoth islands of ice in the Weddell Sea discovered the icebergs attract thriving communities of seabirds above the waterline and a web of algae, krill and fish below.

These mini marine ecosystems may serve to draw down carbon dioxide in the atmosphere and sequester it in deep ocean waters since the algae absorb carbon from carbon dioxide through photosynthesis and then pass it up the food chain.

"While the melting of Antarctic ice shelves is contributing to rising sea levels and other climate change dynamics in complex ways, this additional role of removing carbon from the atmosphere may have implications for global climate models that need to be further studied," said Ken Smith, an oceanographer at the Monterey Bay Aquarium Research Institute (MBARI) in California.

'Too early' to tell

It is too early to say how this phenomenon could affect the efficiency of the Southern Ocean as one of the earth's carbon sinks, a natural depository for human carbon dioxide emissions, Smith said.

But based on their findings and satellite imagery, scientists estimate the icebergs may increase the biological productivity of the Weddell Sea by close to 40%.

The number of Southern Ocean icebergs has increased in the last decade as global warming has led ice shelves to shrink and split apart, but this is the first time that scientists have studied the debris in such detail.

According to the study in the journal Science, Smith and his team examined two icebergs in the Weddell Sea in early 2005, using a remotely operated underwater vehicle equipped with cameras.

The objects were up to 20km long and more than 40m high, with one extending nearly 305m under water.

The researchers found increased concentrations of marine and bird life, in the form of phytoplankton, krill and seabirds such as Cape Petrels, Antarctic Fulmars around the icy platforms up to a radius of 3km.

'Halo effect'

They attribute this "halo effect" to the fact that as the icebergs melt, they shed accumulated terrestrial material "fertilising" the surrounding waters.

The run-off appears to be rich in iron, which stimulates the growth of phytoplankton, the critical building block for the whole food chain.

"The Southern Ocean lacks a major source for terrestrial material due to the absence of major rivers. The icebergs constitute a moving estuary, distributing terrestrial derived nutrients that are typically supplied by rivers in other areas of the oceans," said Timothy Shaw, a geo-chemist at the University of South Carolina.

- AFP