Monday, February 16, 2009

Hi everyone.

Feeling a little brain dead after a long quiet day as we transit to a
site in the middle of the southern ocean, so I can't think of
anything exciting to write about. I did get a question from DT's
class though so I think I'll just go with that.

The question was: is old sea ice denser than new sea ice?

That's a great question, but it's a very tough one to answer. My
guess is there is no simple rule relating density to age. Ice will
in general grow over time (as long as it's below freezing and the
water is cold), so we can generally say that old ice is thicker. But
the mass of the same size block of new and old ice is not as simple.
First of all, there are many types of sea ice (each of which has a
great name -- frazil, shuga, nilas, etc.), and each of which one of
which forms under different environments. The formation determines
the crystal structure which governs how tightly packed the ice is.
This crystal structure will change as the ice evolves and is heated
and cooled from above (by the atmosphere) and below (by the ocean).
Also involved in the aging is a very gradual moving around of salt,
which tends to form channels through the ice. Then snow (which is in
generally lighter than ice) falls on top of the sea ice and may or
may not be incorporated into the ice itself. All of these processes
(and I probably missed others) changes the density of sea ice (as
well as the characteristics that govern its effects on climate),
which make it difficult to generalize.

So if any of the students who asked this wants to consider pursuing
research, this question will probably still be around in some form
when they consider graduate studies.

Good Luck!

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