‘First hint’ of a puzzling change in Southern Ocean revealed by CSIRO

Image credit: theozonehole.com

‘The salinity puzzle’ – something new for climate theorists to ponder and debate. Here they still refer to ‘heat-trapping’ gases, having ignored or forgotten about convection.

Researchers aboard an Australian ship undertaking pioneering work in the Southern Ocean have found the “first hint” of a shift in a decades-long trend towards fresher, less dense water off Antarctica, reports The Age.

Teams of scientists on the RV Investigator have been profiling the salinity and temperature of water between Tasmania and Antarctica at 108 locations. They also released the first batch of deep Argot floats to measure conditions as deep as 4000 metres.

But it is the early analysis of data on salinity in the so-called bottom waters near the seabed that may stir international debate.

“Every time we’ve measured since the 1970s, [bottom water’s] been becoming lighter and fresher,” Steve Rintoul, the voyage chief scientist, told Fairfax Media on Monday as the ship took its final ocean profile.

“We’ve got the first hint now that maybe things are shifting back to becoming saltier and denser in the deepest part of the ocean,” said Dr Rintoul, who is a senior researcher at CSIRO and the Antarctic Climate and Ecosystems (ACE) CRC.

Dr Rintoul said “this increase in salinity still brings levels to nowhere near where they were in the 1970s … nor even into the 1990s”. The trend of warming of those waters has not changed.

Still the salinity puzzle will be an important one to resolve, particularly if confirmed by the 11 deep floats that are starting to send back their once-a-month readings. These deep-water devices, being used for the first time in operational work, will transmit data for as long as seven years each time they surface.

Understanding the Southern Ocean is important not only to improving weather forecasts for Australia. The region surrounding Antarctica is also a “modulator of the global climate”, said Cai Wenju, director of CSIRO’s new Centre for Southern Hemisphere Oceans Research that is also a partner of the Investigator’s research.

While oceans globally take up about 93 per cent of the extra heat trapped in the atmosphere by greenhouse gases, they also absorb about a third of the extra carbon-dioxide released by human activities, such as burning coal.

Of those totals, the Southern Ocean accounts for as much as 75 per cent of the ocean heat sink and 40 per cent of the CO2 dissolved in the seas, Dr Rintoul said.

“Changes in the [deep ocean] circulation would alter the efficiency that the Southern Ocean takes up heat and carbon, and have a big impact on climate,” he said.

Continued here.