April 16, 2019

You Can’t Just Ask Icebergs Why They’re Green

Filed under: Check It Out,Science — Katrina @ 9:54 pm

It’s April. It’s spring. Easter is this Sunday. The Paschal full moon will shine this week. Flowers are blooming. Bees are buzzing. The air is warming up as the days are getting longer.

So let’s talk about icebergs.

Why not? I can think of another mid-April where thinking more about icebergs might have prevented certain disaster…

Sorry. Too soon?

Well, anyway, I’m talking specifically about antarctic icebergs, where, by the way, no flowers are blooming, the days are getting shorter, and it’s of course extremely cold.

Even more specifically, about why some of these icebergs are green.

Glacial ice normally comes in white and blue. White means there’s a lot of air bubbles in it to scatter light, while blue has been so compressed by the snow and ice accumulating on top that the air bubbles are fewer, and blue is the only color reflected.

And yet… somehow there are green ones? What’s that about?

For one, the green icebergs don’t have air bubbles and therefore should be blue. It’s not glacial ice but marine ice, ocean water frozen to the undersides of ice shelves. So something is added to the mix to make the otherwise blue iceberg into a green one. Something… yellow, perhaps?

Must be dissolved organic carbon, a.k.a. bits of dead organisms that got stuck in there. That would make the ice yellow, and yellow is what you add to blue to get green, so mystery solved!

Or not. Blue and green have about the same amount of the yellowing dead organism bits.

Anyway, turns out the green is from iron oxides, which you already know if you looked at any of the above links which explain all this way better than I am and also have some cool pictures. Glacial movement grinds rock into some kind of glacial flour (actual term) which gets caught up in the ocean water that freezes under the ice shelves to become marine ice. This contains yellowish red iron oxides to mix with the blue, so there you go. A chunk of that breaks off the ice shelf and floats away, and that’s how you make a green iceberg!

Okay, but so what? Who cares if some iron-laden icebergs are out sailing around?

Phytoplankton, that’s who! They rely on this iron transport, this ferrum ferry if you will, to bring them some much needed nutrients.

In other words, these verdant bits of ice shelf come rolling in, and phytoplankton are like…

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