Tuesday, 2 April 2013

 Day 19 Greasy Ice Pancakes Anyone?

The excitement of yesterday has finally died down. Those who were fooled by the post and felt embarrassed, rest assured you provided a lot of entertainment and some much needed connection with the outside world for a lot of us! We have to credit Andrew for his Photo-Shop abilities - there is surely a Job for him with Vogue when he wants it - and to JB for his news-website abilities   - Don’t believe everything you read in the papers!

Despite temperatures well below -10C, strong winds and snow, Paul and Phil and the crew press on with their mooring recovery.  During the day the rest of us try to look busy with data processingn and instrument callibration while taking opportunities to spot seals, birds, icebergs and the unrelenting majesty of the environment around us.

 Photo: Paul and the crew recovering a mooring during a fleeting break in the weather.

 Photo: Cape Petrels

It has been so cold we have been able to Sea-Ice form around us. Because the ocean is salty, it doesn’t freeze until the air temperature gets down to around -2C. As this threshold is met, the surface of the ocean begins to look greasy like butter on a fry pan. As ocean waves approach the ‘grease-ice’ they continue but slow down as if they have hit a layer of treacle of honey. As the cooling continues, small round sections of solid ice form which curl up at the edges like pancakes. First there are little pikelettes within the grease, then crepes and  then huge hot cakes. The pancakes raft together with any chunks of weirdly shaped ice left over from previous years.

The ice we see is mostly fresh water. This means that as the sea freezes it leaves a heap of salt behind. This salt forms extra-extra-extra-salty water. If the water is extra salty and extra cold it doesn’t freeze. Rather it sinks. It is a bit like when you poor cold milk into your tea, if you poor it in slowly it will all sink to the bottom. The cold-salty water formed here sinks into the deep ocean (google 'brinacle BBC Frozen Planet' or try to get a copy of BBCs frozen planet to see fantastic time lapse images of salty sinking plumes under sea-ice). 

The water that sinks around these parts is called Antarctic Bottom Water. This is precisely what the moorings are trying to measure. Just like the milk in your cup of tea, the ultimate fate of the bottom water depends on how much mixing goes on as it sinks and spreads out. Which, after all, is what this voyage is about.

 Photos: From grease-ice to small pancakes to large pancakes.

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