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
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