Glass Frogs

My collection of frogs some day needs one of these.

Ice holes

Out in the middle of the frozen Arctic and Antarctic waters are pockets of open water called polynyas (Russian for ‘ice hole’). I first ran across polynyas when I read ‘Ice Station Zebra’ by Alistair MacLean as a teenager - I understand the book was made into a movie in 1968, but I haven’t seen it. A cold war thriller, the novel centers on a nuclear submarine traveling under the Arctic ice pack on a supposed rescue mission that results in sabotage. Getting through the ice becomes critically important to the submarine’s crew - and normal pack ice is much too thick to break through. A polynya provides the perfect way through the ice, but why are they there?

It seems paradoxical that open water can co-exist with below freezing air temperatures. Shouldn’t the water just freeze? Polynyas form only under very special conditions. First, a physical barrier is needed to stop ice from moving in. A point of land or ice bridge would do the trick. Next, mechanisms to stop ice formation must occur which can be broken into two broad categories.

If the forming ice is removed by some mechanical process, it’s called a mechanically forced polynya. Appropriate mechanical processes include wind, currents and tides. Because ice is being formed, then moved away, the surface waters would become extra-salty - as sea ice forms it rejects the brine. This salty, cold water would then sink.

The second type of polynya is formed by convection. Convection is a common heat-transfer process that can be found in any kitchen. It explains how a pot of water is brought to the boiling point from a heat source below. The element heats the bottom layer of water (conduction) and this water rises heating water further up (convection).

In Arctic waters (and Antarctic waters I think - I haven’t been looking into what happens in the Antarctic), the lowest layer of water is quite warm, about three degrees Celsius. It stays on the bottom because it’s dense (i.e. heavy). If a process, like tides or upwelling, brought this warmer water up to the surface, it would keep the surface waters from freezing. An added bonus when deep waters are brought to the surface is that they tend to be nutrient rich, supporting diverse life.

As with everything in nature, polynya formation is complex. Typically, they form due to a combination of factors and can even create their own feedback loops.

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.

Getting tangled in jargon

A crab drawing of mine - completely unrelated to the text

Since I spend most my days with people in ocean science and people who have been around ocean scientists long enough to understand what they say, I often don’t notice ocean science specific jargon as such. I got caught out the other day using ‘water column’ when asked what I do - I didn’t even realize I was using jargon until she said she didn’t know what that meant.

Imagine you are out on the ocean on a rubber raft. If you looked straight down over the side, from the surface of the water all the way down to the bottom would be considered the water column.

On another note - a blog post I wrote about how we measure temperature in the ocean has been posted here.