Frost Flowers Revisited

Somebody asked about frost flowers (thanks, MeghanC!) This gives me an excuse to pontificate upon them a bit. Here’s a great picture of frost flowers from a New Scientist gallery:



Those of you who haven’t spent a lot of time hanging out in the polar regions may not be familiar with the sequence of events involved in the formation of sea ice (apologies if I’ve explained this one before…) As the winter begins and the ocean cools down, little bits of ice begin to form at the surface of the water; these are called frazil or grease ice. Eventually they stick together into a flat sheet, called nilas ice. Pockets of seawater (brine) get trapped between the crystals as they freeze.

As the ice gets colder, water freezes onto the walls of the brine pockets. When water freezes, it tends to exclude any non-water substances, so the brine within the pockets gets saltier. Water also expands as it freezes, so some of the salty brine is pushed out of the ice. Part of it goes downward, and the sinking of this cold, dense, salty water has interesting effects on ocean currents. Part of it goes upward through whatever channels it can find:



Experimenting with hand-drawn diagrams this time, as you can see.

The ice continues to freeze, and the brine being pushed out of the pockets forms a thin layer across the ice. This layer is very salty, so it stays liquid even at very low temperatures:


Frost flowers form at temperatures below -15C (or lower, depending on who you ask.) Seawater, of course, can never get colder than -1.8C. This means that under frost-flower-forming conditions, the ocean is quite a lot warmer than the air. The brine layer on the surface of the newly-formed ice is also comparatively warm, and it gives off water vapor. The vapor re-condenses and forms crystals on top of the briny “bumps” we saw earlier:


The flowers continue to grow, and some of the brine travels up them via capillary action, making them very salty compared to most sea ice:


That, anyway, is the short version of how frost flowers form. They may have some effects on the atmosphere because salts from the ocean are caught in their delicate fronds where the salts can easily be picked up by wind. They may also, as we are now seeing, have some effect on ice albedo both by themselves and by capturing snow that blows across the ice.

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7 Responses to “Frost Flowers Revisited”

  1. Will Says:

    Some of us who do hang out in polar regions had no idea that this was how they were formed…or never really thought much about it at all. Thanks for that write up!

  2. Solomon Says:

    That’s really interesting, thanks. 🙂

  3. Meghan Says:

    Thanks for elaborating! That’s a pretty amazing process.

  4. Julie Says:

    I just think they are beautiful

  5. Teri Carns Says:

    Thanks – diagrams and all — very nice – Teri

  6. deborah Gooden Says:

    Regina, you are amazing and ice flowers are amazing.

  7. Ramon Says:

    Awesome diagrams.

    But I also can’t help wondering how the frost flowers taste and whether they’d be good on french fries. Seriously. Have you seen what they can charge for Mediterranean sea salt? Imagine what one could charge for Antarctic frost-flower salt….

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