Listen to Professor Steve Rintoul on Radio National AM

Deep water on the floor of the Southern Ocean is the coldest and most dense in the world, and has a big influence on how the earth adapts to becoming warmer. But new research indicates the amount of deep water is decreasing, which could have big implications for future climate change.

TOM NIGHTINGALE: Thousands of metres beneath the Antarctic ice, the water is so unusual it’s below zero degrees.

Dr Steve Rintoul from the CSIRO (Commonwealth Scientific and Industrial Research Organisation).

STEVE RINTOUL: The combination of reasonably high salinity and very cold temperatures makes the water the densest or heaviest water that’s found anywhere in the world ocean.

TOM NIGHTINGALE: The below-freezing temperature is due to its salt content. The deep ocean water creates currents that have ripple effects across the world over decades or hundreds of years.

Over the summer, Dr Rintoul led a research team that found those currents are starting to change which might have big consequences for the earth’s climate.

STEVE RINTOUL: It’s early days in the sense that we’ve, we’re just starting to detect these trends but we need to keep making these measurements and determine the cause of these changes so that we can do a better job of predicting how climate will change in the future.

TOM NIGHTINGALE: The deep water had been estimated at about 1,000 metres thick. Now it’s estimated to be a much smaller thickness, on the ocean floor.

STEVE RINTOUL: The changes we’re finding are a response to changes in climate rather than driving changes in climate themselves. So it’s a signal to us that something is going on.

SUSAN WIJFFELS: Especially the deep ocean, it reacts on a 50 to 100 year timescale.

TOM NIGHTINGALE: Susan Wijffels from the CSIRO.

SUSAN WIJFFELS: So once we start moving it, its momentum will move it continue to move it in that direction. And for us to change things and turn it around will also take decades.

TOM NIGHTINGALE: She says the researchers haven’t pinpointed an explanation. But she says it has big implications for measuring the changing temperature of the earth

SUSAN WIJFFELS: Over the long term, it’s really going to be the deep oceans that dictate where we’re going to end up.

TOM NIGHTINGALE: The research was also a significant logistical challenge. At some points the crew’s compasses had to be ignored because they were distorted by being so close to the South Pole.

STEVE RINTOUL: The Southern Ocean is the most, is the windiest and waviest part of the ocean, it has the largest waves of anywhere in the world ocean, it has the largest waves of anywhere in the ocean. And so it makes life both difficult on the ship but also it makes the measurements difficult to obtain.

TOM NIGHTINGALE: Dr Rintoul and others will return to the Antarctic for more testing next summer.

The results from the recent tests will be published later this year.

Heard on ABC Radio National 5th May, Elizabeth Jackon’s A.M. program.