Climate, food chain could be affected by melting Antarctic ice

PHOTO AFP SINGAPORE - Rapidly melting Antarctic ice is slowing down the flow of water through the world's oceans, and could have a disastrous impact on global climate, the marine food chain and even the stability of ice shelves, new research has found.

The overturning circulation of the oceans, driven by the movement of denser water towards the sea floor, helps deliver heat, carbon, oxygen and vital nutrients around the globe.

According to a study published on Wednesday in the journal Nature, deep ocean water flows from the Antarctica could decline by 40 percent by the year 2050.

That's amazing to see that happen so quickly, said Alan Mix, a paleoclimatologist at Oregon State University and co-author on the latest Intergovernmental Panel on Climate Change assessments, who was not involved in the study. It seems to be kicking into gear right now. ALSO READ: Study: Intense El Nio expected to speed up sea level rise.

As temperatures rise, freshwater from Antarctica's melting ice enters the ocean, reducing the salinity and density of the surface water and diminishing downward flow to the sea's bottom.

While past research has looked at what could happen to similar overturning circulation in the North Atlantic - the mechanism behind the doomsday scenario that would see Europe suffer from an Arctic blast as heat transport falters - less has been done on Antarctic bottom water circulation.

Scientists relied on 35 million computing hours over two years to crank through a variety of models and simulations up to the middle of the century, finding deepwater circulation in the Antarctica could weaken at twice the rate of decline in the North Atlantic Ocean.

They are huge volumes of water. In a news conference, Matthew England, an oceanographer at the University of New South Wales, said that they are bits of the ocean that have been stable for a long time.

The effect of meltwater on global ocean circulation has not yet been included in the complex models used by the IPCC to describe future climate change scenarios, but it is going to be considerable, England said.

Ocean overturning allows nutrients to rise from the bottom, with the Southern Ocean supporting about three-quarters of global phytoplankton production, the base of the food chain, said Steve Rintoul, co-author of the second study.

Rintoul, a fellow at Australia's Commonwealth Scientific and Industrial Research Organisation, said if we slow the sinking near Antarctica, we slow down the whole circulation and so reduce the amount of carbon dioxide that gets into the ocean, leaving more CO 2 in the atmosphere.

The study showed warm water intrusions in the western Antarctica ice shelf would increase, but it did not look at how this might create a feedback effect and cause even more melting.

It doesn't include the disaster scenarios, said Mix. It's kind of conservative in that sense.