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Good News / Bad News and how I make measurements

Updated Friday, 30th March 2007

The ship's laundry has opened but the chocolate has run out. Mark Brandon is lowering expensive equipment into the sea in the dark in the middle of the night…

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First the Good news

Friday morning 0114 my time, 0515 UK time and we are in position to make a crucial set of measurements across the George VI Sound. Once we have completed this we should be able to work out how much the entire 25000 km2 George VI ice shelf is melting. What makes this really neat is that other scientists have measured it in the past and worked out it's melting between 3 to 5 m a year. Now any previous measurement in Antarctica is a rarity I can tell you, so once we work the current melt rate, we can deduce whether the ice shelf is decaying more rapidly or slowing down. If the ice shelf melt is increasing then of course we could point the finger at human driven climate change, and ultimately, I guess, our results help our government decide on how to tax us by reducing our CO2 emissions.

But I have just realised I haven’t said actually how we measure if the ice shelves are melting. The principle is easy – you measure the temperature and the amount of salt in the water that flows under the ice shelf, then measure the temperature and amount of salt in the water that flows out. They should be the same if the ice shelf isn’t melting – so any difference we see is caused by melt water from the ice. If you think of it another way, if you have a glass of gin of known alcohol strength, throw in some ice and let it melt, if you measure the alcohol content when you come back you can work out exactly how much ice diluted your alcohol. It's just on a bigger scale, and without the gin.....

Good News / Bad News and how I make measurements inline 1 Copyrighted  image Icon Copyright: Mark Brandon
Deploying a CTD.

That’s the principle, but in practice you have to be super accurate which is not so easy in -20°C. To measure the temperature and salinity of the water flowing under the ice shelf our ship first has to break a hole in the ice for us, then we lower a piece of equipment called a CTD over the side of the ship all the way down to the sea floor. Its called a CTD because it measures Conductivity (that is the amount of salt), Temperature and its Depth. Now CTDs are pretty expensive – the one we are using costs about the same as a brand new Ferrari, and we lower it through the ice on a small cable about 1cm in diameter sometimes down to 3000 m, and get to within about 4 m of the sea floor. If it touches the sea floor – that’s very very bad – we could lose it. But at the same time we want to get as close to the bottom as possible so we measure all the water beneath the ship.

And all the time the ship is being bashed around by the sea ice. Its OK work when the Sun is out, and it’s the middle of the day, but as I type this it's dark again and we are in ice almost 4 m thick and being menaced by a couple of icebergs that can't decide which direction to drift in. I don’t sit here worrying about the cost of the kit – but I have to be pretty responsible about the risks I take.

By the time my 12 hours watch is up I am ready for a break.

More good news

The ship has a strange and unfamiliar smell…. Soap powder! Big thanks to the engineers - they have managed to make enough water to open the laundry again.

And the bad news...

Say it quickly so it doesn’t hurt so much.

This part of Antarctica has run out of chocolate.

I am in shock.

 

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