Transcript

Life in the polar seas

INTERVIEWER

Mark, ice doesn't behave the same way at the different poles, does it? So how does it vary?

DR. MARK BRANDON

Well, one of the things that affects the ice most of all is the basic geography. In the Arctic, you've got land and then a deep ocean in the middle. Whereas in the Antarctic, you've got land in the middle and deep ocean around the edge. If you go back to the Arctic, in winter, all of that Arctic Ocean gets frozen over with what we call sea ice, which is a very thin layer of ice, only perhaps two or three metres thick. It extends out - about 15 million square kilometres of the ocean gets covered by this sea ice. And it is a bit like if you think of polystyrene floating on the sea, it gets blown about by the wind. So the sea ice is constantly moving and constantly drifting around and grinding up. So if you hear about ice being thicker that three metres, it's usually two ice flows of three metre thickness that bumped into each other, one on top of the other.

INTERVIEWER

So all this floating ice in the Arctic, it does collide, I would imagine. It forms ridges, does it?

DR. MARK BRANDON

It does. And if you actually go online, there's the International Arctic Ocean Buoy Project, IOEB. And you can actually look at the drift tracks of buoys that are actually out there right now, sending back weather data from the Arctic Ocean, that drift with the sea ice. and so you can look at these fantastic movies of how the ice drifts.

INTERVIEWER

How does ice behave in the Antarctic, not in the same way then?

DR. MARK BRANDON

Well, the seasonal change between the Arctic- in the Arctic, about 2/3 of the ice disappears between the summer and the winter. In the Antarctic, almost all of the ice disappears in Antarctic summer.

INTERVIEWER

Where does it go to?

DR. MARK BRANDON

It melts away. So there are only a couple of small areas, mainly the Ross Sea and the Weddell Sea and quite close to the coast. Because when I say most of the ice disappears, there's about 2 million square kilometres of ice still in the Antarctic. But compared with Antarctic winter, that 2 million square kilometres of ice grows another 15 million square kilometres. So it really is just the remnants of a vast amount of ocean covered by ice.

INTERVIEWER

And for the permanent ice, we're talking about some incredible thicknesses as well, aren't we, in the Antarctic particularly?

DR. MARK BRANDON

Well, if you look at Antarctica, it's a continent. It's land. And then snowfall, over millions of years, gets compressed and turned into ice. And individual layers of this snow build up thickness of ice. And this started happening, this snowfall, maybe 35 million years ago. And the thickness of ice now, on East Antarctica, the east part of Antarctica, is about three kilometres thick. And that's made entirely of snow. So it's fresh ice. It's the sort of stuff that, when it reaches the edge of the continent, this land ice, it can either form an ice shelf, which is a large, thick shelf of ice, perhaps 200 or 300 metres thick. Or the glaciers can fall straight into the sea and form icebergs. Whereas the sea ice is just frozen seawater, and so anything that's in the sea water gets trapped within the ice. And it's quite a porous thing, sea ice, compared with land ice, because it's formed from ice crystals growing in the water, rather than snowfall being compressed.

INTERVIEWER

So there's life within this sea ice.