Deep ocean currents at Antarctica that circulate a crucial part of the food chain are set to significantly weaken, a new study shows.

The Australian research published in the journal Nature shows that unless significant cuts in emissions are made the currents could weaken by 40 per cent in the next 30 years, and could be headed for collapse.

Cold water that sinks near Antarctica drives a deep flow of water around the globe.

It carries heat, carbon, oxygen and nutrients, and has been stable for thousands of years.

The new study predicts it is heading for a "dramatic" slowdown with consequences to be felt for centuries to come.

Report co-author Dr Steve Rintoul, from the Australian Antarctic Program Partnership, says it will block crucial food that support our fisheries.

"Nutrients exported from the southern ocean support about three quarters of global phytoplankton production, the base of the food chain."

It will cause water at the ocean bottom to stagnate, affecting marine ecosystems from the second half of the century.

The slowdown is being driven by meltwater from Antarctica, and is tipped to happen at double the rate of the northern hemisphere's North Atlantic Ocean circulation.

Simulations run for the study took a couple of years to run on the best supercomputer in Australia, totalling about 35 million computing hours.

Aotearoa Antarctic Research Centre director Professor Rob McKay says it's groundbreaking research.

He says the ocean absorbed a great deal of carbon from the atmosphere, acting as a brake on warming.

The study shows this will be disrupted, causing a feedback loop which increases temperatures creating yet more meltwater, says McKay.

"Whether or not the earth is capable of absorbing the carbon in the same way it has been is a fundamental question."

McKay says it will also drive even greater sea-level rise than is already predicted.

"If you get this amplifying effect ... that will have an impact on sea-level rise which we know is an imminent threat for many of our coastal communities."

The drastic slowdown is based on scenarios where humans fail to slash emissions effectively.

Rintoul says decisions today count.

"It is another wake-up call - as if we needed more wake-up calls."

University of New South Wales Professor and report co-author Matthew England says slashing dangerous climate gases could ease the impact.

"It's hard to turn the ship around with this sort of physics, but by mid-21st century there's no doubt that emissions reductions would lower our meltwater input around both ... Greenland and Antarctica, and that would make a difference."

There's already physical evidence of the slowdown effect predicted by the modelling, he says.

-Hamish Cardwell/RNZ.