From the Antarctic: Sea urchins pay cost of ozone gap

By SIMON COLLINS at Scott Base

"It's not really that cold", said Brian Grant over dinner at Scott Base, after a day spent diving with his daughter's Barbie doll in the coldest water in the world.

It certainly didn't look like the pleasant waters of Leigh as the Otago University diving safety officer grimaced and fretted before plunging through the ice covering Antarctica's McMurdo Sound into -1.9C seawater.

He went down once to the ocean floor to retrieve an instrument measuring the amount of ultraviolet light that penetrates the three metres of surface ice and 15 metres of water underneath.

He went down again to pick up another UV-recording device that was pinned to the bottom of the ice layer by a pumped-up tyre. Though originally held up just by the tyres' air, it had stuck to the ice and he had to prise it loose by hand.

In between, he photographed not only two large seals that were swimming with him, but also his 9-year-old daughter Jacinta's favourite Barbie doll performing gymnastic antics on the seafloor.

Later that night, he emailed the photos back to Jacinta in Dunedin, as he does almost every night. Everywhere he goes, the Barbie goes.

"It gives her a connection with what I'm doing," he said.

But although he took the Barbie down with him, he said he did not set up its poses.

"I was photographing the seals and just noticed the Barbie when I looked around, he said.

It had been picked up by the ocean currents and looked as if it was dancing at the bottom of the sea."

Dr Miles Lamare, the Otago University scientist in charge of the four-week diving programme, says the instruments Mr Grant retrieved confirmed that there was a much higher ratio of harmful UV-B light to visible light under the sea ice this year than last year.

The sea ice was half a metre thicker because of a big iceberg which has blocked the entrance to McMurdo Sound and kept Scott Base icebound for the past four summers.

The extra-thick ice reduced the visible light getting through to tiny larval sea urchins that live under the ice.

In other years, visible light would have helped the larvae to repair the damage done by UV light.

But this year the ozone hole above Antarctica was much bigger than last year, letting more UV light through.

Although this, too, was partly offset by the thicker ice, the net effect was to leave the larvae more exposed and less able to repair the damage.

The near-freezing Antarctic waters absorb twice as much oxygen as water at the tropics.

The extra gas pumps up some crawly isopods to 20 or 30 times the size of their New Zealand relatives, the garden slaters.

But it also exposes Antarctic sea dwellers to far more dangerous free oxygen atoms, or free radicals.

Organisms such as sea urchin larvae have to spend so much energy just surviving in the cold that they have very little spare energy to cope with the extra free radicals that the UV light throws at them.

"They are finely tuned. Any increase in metabolic costs would be more costly to them," Dr Lamare said.

The diving research has proved that, even last year when the ozone hole was unusually weak, exposure to UV light through the sea ice slowed the larvaes' development and increased their death rate.

He said "greenhouse" gases such as carbon dioxide from car exhausts were prolonging the ozone hole, even though in the 1990s the world banned CFCs, the substances used in aerosols and fridges that were first blamed for the hole.

"So predictions go from 25 to 50 years more of a continued ozone hole", he said.

Mr Grant and his daughter's doll may have to make many more icy dives yet before his work helps to alert the world to the ultimate costs of our comfort and convenience in the Barbie era.