Monday, 15 March 2010

Here's a quick look at some of the sea ice I'm studying at the moment. It grew over the winter of 2009 in McMurdo Sound (this year's batch is just getting going). We get the ice using a large hollow drill, or corer, giving us a solid cylinder of ice. By scratching an arrow on the top, and piecing the cylinders together carefully, we can work out which way was North and we mark that with a thin cut along the core. We then take the core back to Scott Base where I chop it up using a meat-saw in a frozen laboratory, then measure it with instruments, all at -20 degrees C.

This video shows thin slices of the ice (each one is about 9cm diameter, 1cm thick) photographed under crossed polarisers. The video starts 70cm into the ice and finishes around 148 cm in, representing growth for around 70 days. Individual crystal grains show up as different patches of dark or light, and you can follow them as they grow downwards. Currents below the ice, inputs of small seed crystals and growth of platelet crystals into the ocean change the crystal make up of the ice as it grows. Early on currents help to align the ice crystals, later small seeds appear and disrupt the existing crystals, finally the first stages of platelet ice appear.

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