The cold hard facts

Alex Gough of the University of Otago Department of Physics takes notes as an oceanographic mooring is raised from beneath the sea ice in the Antarctic. The mooring was in place throughout the winter and its rope acquired a growth of platelet ice, which is steaming in the cold air. This kind of ice is rare in the Arctic and may be one of the reasons why Antarctic sea ice is not behaving like sea ice in the Arctic. Photo by Andy Mahoney.

There are really quite intimate links between global climate and sea ice

Most of us know there are different kinds of ice: there's the ice cubes in our gin and tonic and the ice that forms in the back of the freezer.

Few of us think much deeper about ice. But some scientists are so interested they were happy to spend last winter in the dark on the Ross Sea, New Zealand's patch of Antarctica, in temperatures down to minus 50degC, studying ice.

They measured its thickness. They dissected it and studied its crystals, which look spectacular in a certain light. They melted it to see how salty it was. They worked out how quickly it grew. They took its temperature.

Some might wonder why our tax dollars are used to fund such research - putting up three men in heated shipping containers to drill holes in the sea ice which forms a skirt around the Antarctic ice shelf in winter.

Of course, they weren't only interested in the sea ice: they studied the water beneath - its temperature, salinity and the currents.

The scientists say what happens to sea ice has a ripple effect around the globe, influencing even the temperatures in which we enjoy that G and T.

The polar climate has a major effect on world climate. The ice acts like a mirror to reflect heat back into the atmosphere, and moderates atmospheric temperatures by locking up energy as it freezes.

And the sea ice, which doubles the size of Antarctica in winter, is indeed different from the permanent ice shelf - forming from salt water whereas the ice shelf forms from freshwater snow off the continent. Different forces are at play in its formation.

The continued appearance of sea ice in winter is important to the food chain beneath, from the algae that forms on the bottom of the ice to the whales that feed on krill in the deep ocean.

As it forms the salt is rejected, increasing the water's salinity and density. It sinks to the depths, carrying oxygen which supports marine life and contributing to the circulation of the oceans which move heat around the planet. And if the water is warmer, it warms the air above it.

Changes in the sea ice are also an important indicator of climate change - as its dramatic retreat in the Arctic suggests. But in the Antarctic, supercooled waters from the melting ice shelf are thought to be one reason why annual sea ice formation has not declined.

Scientists at the University of Otago, Niwa, Victoria University and Industrial Research Ltd (a Crown research institute) with Antarctica NZ's support are jointly working to better understand the processes influencing sea ice formation in the Ross Sea: the interrelationships between the ice shelf, ocean and atmospheric conditions and sea ice.