Global Warming Could Starve Oceans Of Oxygen - Study

NORWAY: May 2, 2008

OSLO - Global warming could gradually starve parts of the tropical

oceans of oxygen, damaging fisheries and coastal economies, a study

showed on Thursday.

Areas of the eastern Atlantic and Pacific Oceans with low amounts of

dissolved oxygen have expanded in the past 50 years, apparently in

line with rising temperatures, according to the scientists based in

Germany and the United States.

And models of global warming indicate the trend will continue because

oxygen in the air mixes less readily with warmer water. Large fish

such as tuna or swordfish avoid, or are unable to survive, in regions

starved of oxygen.

"Reduced oxygen levels may have dramatic consequences for ecosystems

and coastal economies," according to the scientists writing in the

journal Science.

The north of the Indian Ocean, along with the Arabian Sea and the Bay

of Bengal, is also oxygen-low but the available data showed no

substantial change in the size of the oxygen-minimum zone in recent

decades.

Lothar Stramma, lead author at IFM-GEOMAR in Kiel, Germany, said there

were signs the oxygen-low bands between 300 and 700 metres depths were

getting wider and moving into shallower coastal waters.

"The expansion of the oxygen-minimum zones is reaching more to the

continental shelf areas," he told Reuters. "It's not just the open

ocean." That could disrupt ever more fisheries.

Problems of lower oxygen supply add to woes for the oceans led by

over-fishing as the world struggles to feed an expanding population. A

UN conference in 2002 set a goal of trying to reverse declines in fish

stocks by 2015.

The scientists said levels of dissolved oxygen in the oceans had

varied widely in the past and more study was needed. "We are far from

knowing exactly what will happen," Stramma said.

In the most extreme case, at the end of the Permian period about 250

million years ago, there were mass extinctions on land and at sea

linked to high levels of carbon dioxide and extremely low oxygen

levels in the waters.

The UN Climate Panel said last year that global warming, stoked by

human use of fossil fuels, would push up temperatures and bring more

droughts, floods, heatwaves and rising sea levels. More and more

species would be at risk of extinction.

Thursday's study showed that a swathe of the eastern Pacific from

Chile to the United States and a smaller part of the eastern Atlantic,

centred off Angola, were low in oxygen.

Stramma said the oxygen-poor regions were away from major ocean

currents that help absorb oxygen from the air. And warmer water is

less dense and so floats more easily -- that makes it less prone to

mix with the deeper levels of the oceans.

(Editing by Matthew Jones)

Story by Alister Doyle

REUTERS NEWS SERVICE