Dispatch 18: Gradations of Sea Ice     Print

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Fred Marin

September 29, 2019

Our steam south through the Arctic feels southern compared to where we had been as open waters and waves now surround us.  The air is warmer than it had been, and overall it feels like we are now on a normal ship, in a normal watery ocean instead of a heavy icebreaker crushing and shuddering through plains of ice as far as the eye can see.

As mentioned before, Kazu Tateyama from the Kitami Institute of Technology, and his team of students have been focused on studying the sea ice itself.  One of the features of the ice they were studying was its crystal structure on a variety of size scales.  After our ice stations and their collection of samples, I found them in the lab processing the ice cores they had taken.  This team is forever creative as they found a way to cut the ice core into thin sections without the use of a slicer.  Carefully cutting the core with an ice saw, they then melt it to be glassy smooth and flat using a hot plate.  Kazu explained to me that they were not able to bring their core slicer so this was a close substitute.  The slices were then sandwiched between two sheets of polarized tint with each tint being orthogonal to one another.  This revealed a dramatic image of the ice structure.  The amazingly crisp images they captured will be brought home for in depth analysis. 

The Arctic Ocean is some of the coldest water on Earth, it’s about ~1.5° Celsius which is below freezing because salty seawater freezes at ~1.8° Celsius. I still find it interesting that sea water is salty, but sea ice is not.  When salt water freezes, the salt is extruded making the water around it even saltier. The salt melts brine channels in the sea ice forming a matrix of tiny holes in the ice.  With the sea ice team, we ate a couple pieces from the core to see if we could taste any salt still trapped in the channels.  We all agreed the samples all tasted the same, like fresh water.