Ozone hole changed ocean

The University of New South Wales Science Alert 5 Feb 13;

The formation of the Antarctic ozone hole has caused changes in the way waters in the southern oceans mix, with possible impacts on climate change, a new study suggests.

To trace the movement of ocean waters from the surface into the ocean interior - a process known as ventilation - researchers analysed ocean concentrations of a chemical that was used in hair spray cans, refrigerators and air conditioning systems before it was phased out in the 1990s because it was destroying the ozone layer.

The study, by an international team which includes Associate Professor Mark Holzer, a mathematical scientist at UNSW, is published today in the journal Science.

They found that surface waters are mixing into the subtropical deeper ocean at a higher rate than 20 years ago, while the reverse is true for waters closer to Antarctica.

Dr Holzer said the find was consistent with the fact that surface westerly winds in the southern hemisphere, which drive the ventilation of the southern oceans, have strengthened in recent decades.

Other studies have attributed this wind intensification to the thinning of the ozone layer.

“It is fascinating that changes in the stratosphere have had an effect down to at least 1500 metres depth in the ocean,” said Dr Holzer, from the School of Mathematics and Statistics in the Faculty of Science.

The movement of surface waters into the deeper ocean governs the ocean’s uptake of heat, oxygen and carbon from the atmosphere.

“And all of these are potentially important for changes in the global climate. Ventilation is the way the ocean communicates with the atmosphere,” Dr Holzer said.

The team, led by Professor Darryn Waugh, of Johns Hopkins University, used measurements made in the southern oceans in the early 1990s and in the mid- to-late 2000s of a chemical compound called chlorofluorocarbon-12, or CFC-12.

CFC-12 was first produced commercially in the 1930s and its concentration in the atmosphere increased rapidly until the 1990s, when it was phased out by the Montreal Protocol that governs ozone-depleting compounds.

Higher concentrations of CFC-12 than predicted for an unchanging ocean were found in deep water from about 25 to 45 degrees south, reflecting an increased influx of surface water to these latitudes in the past 20 years.

The study concluded the opposite was the case for polar deep waters, where there has been increased upwelling.

Dr Holzer said the use of CFC-12 was an interesting twist: “The very substance that contributed to destroying ozone is helping us figure out what is happening in the oceans.”

Professor Waugh said that recovery of the ozone layer during the next 50 years could slow down the changes in ocean ventilation, but continued increases in greenhouse gases could also have an effect on ventilation.

The combined impact of these two factors on the oceanic uptake of heat and carbon remained an “open question”.

“Any changes in southern ocean circulation have the potential to change the global climate,” Professor Waugh said.