Tuesday, July 10, 2012

making ice

Sea ice in the Beaufort Sea
I took thermodynamics in 1992 - just the other day was the first time I needed it. Formulas memorized 20 years ago are long gone from my head forcing me to crack open old textbooks. I've been moving these books around for years, so it's good to finally need them.

The first book I looked at was a first year oceanography textbook where the authors seemed confused about the difference between heat and temperature. An undergrad physics textbook turned out to be much clearer.

Heat and temperature are related, but they are not the same thing - a point that is often blurred in our everyday language. Temperature is a physical property of an object and easy to measure with a thermometer. For my project, I spent a lot of time last summer measuring this property in seawater and I'm planning on gathering more of this data in a few weeks. Temperature puts a number to ‘hotness’ or ‘coldness’.

We know that the molecules making up everything are in constant motion. The energy found in this motion is know as heat which is reported in joules.

Why am I suddenly looking at heat and temperature? I want to know if cold winter waters produced in Cumberland Sound will form the bottom water which is over one kilometre deep. If I can’t make this water locally, then it must come from somewhere else. To see if bottom waters are being made in winter (as I don’t have data from that time) I’m cooling down the summer water (which I measured) to the freezing point, making it denser. Then, I’m looking at the denser water to see if it will sink to the bottom. The temperature difference between the summer value and the freezing point is related to the heat loss - so I’m also able to look at the amount of heat that needs to be removed and see if that number relates to winter conditions.

These calculations are very rough as ice formation is much more complex than just cooling surface waters to the freezing point - but, it's a place to start.

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