Drift or pack ice

Sea ice breaking out
Sea ice breaking out (Photo: Vicki H)
The Aurora Australis in sea iceSea ice near Casey stationSea ice forming near the Davis beach

Pack ice is the term used in a wide sense to include any area of sea ice other than fast ice no matter what form it takes or how it is disposed. The majority of ice occurring in a wide band around Antarctica is referred to as ‘pack ice’. This is a region of highly variable ice conditions, including broken pieces (floes) with a range of sizes, ages and thicknesses, present in varying concentrations.

The pack is highly mobile, moving with the wind and currents, with its characteristics constantly changing. There is frequently some open water (leads) between the floes and it is common to see ice at various stages of development present in the same area. This is the result of the dynamic nature of the pack, with the thickness of floes increasing through ‘rafting’ and ‘ridging’ as they interact, and new open water areas constantly being created, allowing new ice to form.

Rafting and ridging 

Rafting is the pressure process whereby one piece of ice overrides another, and is most common in new and young ice. Ridging is the process by which sea ice is forced into a line or wall of broken ice forced up by pressure. It may be fresh or weathered. The submerged volume of broken ice under a ridge, forced downwards by pressure, is termed an ice keel.

Cake ice

Cake ice is commonly used in Antarctica to refer to a collection of ice cakes. This should not to be confused with pancake ice. Cake ice is older and thicker than pancake ice.

Ice breccia 

Ice of different stages of development frozen together.

[Video]

Sea ice drilling: Mawson to Auster Rookery

Video transcript

I spy with my little eye, something beginning with ‘I’!

‘I’?

Idiot!

These is Pete, Mark and we’re expeditioners for the Australian Antarctic Division and today we’re drilling the sea ice.

I spy with my little eye something beginning with ‘s’!

‘s’?

Ahhh, snow! Snow!

Mark, why do we drill the sea ice, mate?

We’re just proving the Mawson to Macey route which is the main route out to the Auster Rookery.

And what’s the minimum distance we need?

We need about 600 mm – we need 600 mm to drive the Hagg on it.

Turn around, look at that – we’ve got a good 685, 690.

How good is that mate?

That’s excellent.

[end transcript]