Monday, 25 March 2013

Day 11 Seeing through the fog

The weather is harsh today. The sky is low, dark and misty. Rain tumbles down over the deck.  Winds of 30knots lash the sea causing rippling pulsations along the surface. If the scene wasn’t hostile enough, a floating Eagrit is seen from the observation deck. It is one of the birds we had seen a few days earlier, disoriented having lost their way. It has not been able to stay in the air any longer and will now surely drown.

Photo: Not much hope left for this little one.

The swell is modest so we can continue to take water samples. The VMP – the device which is used to measure turbulence – is held back. Because the VMP is released and then recovered, John and Alex (its custodians) are reluctant to deploy it if there are too many whitecaps or a thick fog. Both of these would make it all the more difficult to find on recovery.  This frustrates Jean-Baptiste and many of us. A major focus of this project is to measure mixing of the blob. But, to reconcile these, we need direct measurements of that mixing.  In the mid afternoon the weather is rough but the forecast good, so we give it a go. The mist thickens into the night and the VMPs fate is on tenterhooks. All lights are turned off on the bridge and we scour the opaque landscape. Finally, a flash from its light is spotted. The VMP is not lost and another precious measurement is taken.

Photo: Andrew and Jean-Baptiste ‘wake-up’ and ARGO float.

Between measuring the blob and turbulence etc. we are contributing to a broader oceanographic mission. We have on board 6 autonomous buoys called ‘Argo floats’. Up until the early 00’s, if you wanted to know what the temperature and salinity was in the ocean, you had to go out on a boat and measure it - like we are doing now. These days most of it is done by ARGO buoys. Thanks to advances in technology, satellite communication, a fair amount of money (driven by a real need to understand the ocean’s role in climate), and collaboration between all the major oceanographic centres in the world, ARGO floats are now everywhere.

Photo: Deployment of the float.

An ARGO float is basically a thermometer attached to a big piston. The piston compresses a fluid, which makes the ARGO float dense, so it sinks. When the piston is released the float is more buoyant so it floats to the surface. When at the surface, ARGO buoys can send messages via satellite thanks to what is effectively a mobile telephone stuck to the top. They phone home to let us know how warm it is in the deep ocean. So they are bit like a teenage son or daughter away on a gap year. You can’t control where they go but can only hope they will phone home from time to time to tell you how they are getting on (collect calls only…of course).

Image: Distribution of ARGO floats by the country that deployed them. There where more than 3000 in 2010. The serial numbers on ours reads close to 6000.

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