Oxygen-starved oceans rapidly dying
The world's coastal oceans are in crisis, with oxygen-starved 'dead zones' increasing by a third in just two years as global temperatures increase with climate change, according to the International Whaling Commission's latest scientific report.
Dead zones, caused by over-enrichment of waters by nutrients from run-off, sewerage and warming waters, represent 'the worst-case scenario for coastal biodiversity' and are the 'severest form' of ocean habitat degradation, the report says.
The number of ocean dead zones has grown from 44 areas reported in 1995 to more than 400, with some of the worst oxygen-starved areas extending over 22,000sqkm.
Recent figures from the United Nations Environment Program estimate fertilisers, sewage and other other pollutants, combined with the impact of climate change, have led to a doubling in the number of oxygen-deficient dead zones every decade since the 1960s.
The growing list of dead zones includes waters in the
A recent study listed
The commission's 2008 State of the Cetacean Environment Report lists a growing number of concerns over the impacts of climate change and ocean pollution on the world's whales, dolphins and porpoises.
The report says low-oxygen waters at depths of 300m to 700m have expanded in tropical oceans over the past 50 years as the oceans warm. Areas previously rich in oxygen have become 'oxygen minimum zones' containing less than 120 micromoles of oxygen per kilogram of water. It says these reduced oxygen areas will have 'dramatic consequences' for marine ecosystems because fish, squid and crustaceans cannot survive in them. The worst-affected areas are in tropical regions of the
The commission's report says skin diseases are now more frequent among whales and dolphins and may be linked to ocean pollution or climate change.
It says ocean surface warming and the southward displacement of Southern Ocean currents will reduce the feeding grounds of humpback, blue, fin, sperm and southern right whales.
Climate modelling shows 30 per cent of ice cover will be lost in the
Zones of death are spreading in oceans due to global warming
Marine dead zones, where fish and other sea life can suffocate from lack of oxygen, are spreading across the world's tropical oceans, a study has warned.
Researchers found that the warming of sea water through climate change is reducing its ability to carry dissolved oxygen, potentially turning swathes of the world's oceans into marine graveyards.
The study, by scientists from some of the world's most prestigious marine research institutes, warns that if global temperatures keep rising there could be "dramatic consequences" for marine life and for humans in communities that depend on the sea for a living.
Organisms such as fish, crabs, lobsters and prawns will die in such zones, warned Lothar Stramma of the Leibniz Institute of Marine Sciences in
In the study, published in the journal Science, they collated hundreds of oxygen concentration readings taken over the past 50 years in the
In the central and eastern tropical
The researchers found that such regions now extend deeper into the oceans and closer to the surface. Fish and other sea life cannot survive in such waters, said Sprintall.
The researchers say the change is closely linked to rising sea water temperature. At 0C, one kilogram of sea water can hold about 10ml of dissolved oxygen but at 25C this falls to just 4ml.
This impact is amplified by a host of other factors. One of the most important is that parts of the eastern Atlantic, eastern Pacific and the
Examples of partly dead zones include a stretch of the Pacific about 5,000 miles wide off the west coast of
Additionally, as surface water heats up it becomes less dense and forms an insulating layer that stops oxygen percolating into the colder layers beneath.
Climate change is also suspected of altering the direction and strength of ocean currents, causing dead zones such as the one that suddenly appeared off
Lisa Levin, professor of biological oceanography at Scripps, and a world expert on the expansion of oxygen depletion in the oceans, predicted that similar zones would eventually appear off
Around the world there are already around 150 areas suffering from low or declining oxygen levels, she said.
Many of these are close to coastlines where the main cause is not climate change but pollution, especially agricultural chemicals washed off the land. The nitrogen in such run-off effectively fertilises the sea, causing a sudden bloom of algae and other planktonic life.
As such organisms die they are decomposed by bacteria that multiply so fast they suck all the oxygen from the water.
A report by the United Nations Environment Programme found that such coastal dead zones have doubled in number since 1995, with some extending over 27,000 square miles, about the size of the Republic of Ireland.
Among the worst affected are the Baltic Sea, the Black Sea, and parts of the
Recent research has revealed that about 250m years ago average oxygen levels in oceans fell almost to zero a reduction associated with dramatic changes in climate that resulted in the extinction of 95% of the worlds species.
© Copyright 2008 Times Newspapers Ltd.
Global warming could starve oceans of oxygen: study
Reuters, May 1, 2008
Areas of the eastern Atlantic and
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
Lothar Stramma, lead author at IFM-GEOMAR in
"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 U.N. 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 U.N. 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
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.