Sea ice vs glacier

You may remember the difference between sea ice and glacial ice. Sea ice is frozen ocean water, whereas glacial ice is formed on land by the slow accumulation of snow. Sea ice can be up to a few metres thick, although when we are next to it we only see 50cm or so, whereas glacial ice is several kilometres thick in central Antarctica. Sea ice, we can break to go further; glacial ice, we can’t. Now, in practice, what does it look like?

Let’s start with sea ice! Sea ice has a completely different aspect, depending on which part of its “life” you see. With the naked eye on a sunny day, you can work out where sea ice is about to form: the sea there will be totally flat and calm. Then some kind of small ice crystals will start to appear at the surface, and grow to form pancakes of ice (yes, that’s the official name):

Pancake ice, actually from Antarctica

Pancake ice, actually from Antarctica

Then these pancakes will keep growing and merge with other pancakes to create a large continuous surface on which snow will fall. You then obtain the typical sea ice: a thin, smooth white layer, whose thickness depends on how old it is. Note that older ice turns blue as the air is expelled – normally the blue is underwater, and white at the surface, but we can see the blue ice when we break through it:

Blocks of ice broken by us a few days ago

Blocks of ice broken by us a few days ago

There is one easy way to tell Antarctic sea ice from Arctic sea ice: melt ponds. I think that is because the Arctic is warming more than Antarctica, or maybe because Arctic ice tends to be older than Antarctic one, and hence have more time to form melt ponds, but anyway here the sea ice is covered in melt ponds. The air melts the top of the sea ice, forming little ponds, and revealing the older blue ice below.

Melt pond in an ice floe

Melt pond in an ice floe

Arctic sea ice also looks quite “tortured” to me. Where we are now, the ice accumulates over time, resists summer melt, is pushed by the wind until it merges with other blocks… That creates ice sculptures that are a few meters high:

The ice monster keeping an eye on us

The ice monster keeping an eye on us

Sometimes, bits of glacial ice get trapped in the sea ice. These are called icebergs or bergy bits. Glaciers calve, i.e. bits of it break free, and these bits travel with the winds and ocean currents until they eventually melt:

A bergy bit, maybe coming from Petermann

A bergy bit, maybe coming from Petermann

We only came face to face with Petermann Glacier today, so I have fewer pictures for the moment. But to give you a sense of scale, the top of the ice is about 5m above sea level, while the cliffs behind are 500 m high or so. And you can’t see that, but we have a lot of wind today. Anyway, please finally meet the ice tongue of the glacier that fills the fjord:

The terminus of Petermann ice tongue

The terminus of Petermann ice tongue

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