Submitted by Anonymous on Thu, 07/21/2011 - 14:38
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High Arctic Change 2011

CTD stands for Conductivity, Temperature, and Depth. What is the Conductivity of water?

What does a badly wound cable consist of and how does it interfere with one's ability to use the devices?

Thu, 07/21/2011 - 22:57

Mark Goldner

Hi Enrico! Great to hear from you.Thanks for asking about the cable winding - I guess I did a poor job explaining that. So the deal is that we use 1/8" steel "wire rope" cable (picture a stranded rope, but made out of wire) to lower many of our devices into the water and to lift them out. Some of the devices, like the gravity corer, are quite heavy, which is why we use wire and not rope. The problem is that when you wind it up on the winch (which is the spool on which the cable is wound, and it has a handle to make the lifting much easier), if it gets loose then the cable can start to tangle on itself. Then it gets stuck and you can't use it. Somehow over the past couple of years the cable had become loose or someone had used it previously and not paid attention to winding it nicely and tightly. So we had to unroll it and re-wrap it. I'll try to post a couple of pictures of the winch with the cable on it so you can visualize what I'm talking about.
As for your conductivity question, the units of conductivity are "Siemens per centimeter" (S/cm) which is a measure of how well electricity can flow a certain distance. (A "Siemen" is a measure of electrical conductance, which is how well electricity can flow - it's the opposite of Resistance). Actually we measure electrical conductivity of water in micro-Siemens per cm, or µS/cm (because even though we think of water as being a "good" conductor, compared to things like metals it's actually not a very good conductor). OK, now that I have the units out of the way, the conductivity of pure water is 0.055 µS/cm. The conductivity of your tap water is about 100 µS/cm - it's so much higher because there's all sorts of ions dissolved in the water that help keep things from growing in it, and that give it taste, etc. The conductivity of salt water is around 5000 µS/cm. You can see a big difference here.
Great Questions!

Fri, 07/22/2011 - 15:06

Anonymous

Thank you for your time and detailed replies. I didn't expect to hear back from you so soon!P.S. I saw the "Polar Plunge" pictures. You are a brave man, I certainly wouldn't have jumped into THAT water!