10 May 2010 hulten   » (Apprentice)

The real ocean

For half a year I work at the KNMI now, working an modelling of the ocean biogeochemistry, tending to use only free software. Now for something in the context of my work which is mostly unrelated to computing: a cruise over the Atlantic to collect measurements!

Two cruises have been planned for the GEOTRACES project for this year. One will cover the course Reykjavíc--Hamilton and the second the course Hamilton--Fortaleza. Before the start of these cruises the equipment had to be tested on a shorter cruise, which I joined. This small cruise started from Texel and the original plan was to go to Reykjavíc (Iceland). Here the researchers for the bigger cruises would get on the ship. However, in view of the volcanic activity on Iceland and all the air traffic problems resulting from it, it was decided to go to Scotland instead.

We planned to leave the port at Texel on the 22nd of April but, as often happens with preparations, things got delayed. Added to this, we needed high tide to sail out to sea. This is why we left on Friday the 23rd of April. The North Sea was calm and the sun was shining. It was my birthday, so we ate pie and I got a book which was later signed by everyone on board.

The next day the weather was grayer and I got sea sick in such a way that I did have a chance to participate in or observe any activities on board.

On the third day, April 25, the Very Large and the Ultra Clean sampling systems were let down and pulled up successfully. Both systems contain 24 samplers, each twelve litres in volume. The Ultra Clean is especially useful for the measurement of metal concentrations, because the system is mostly made of plastic to prevent the water from getting into contact with metal.

Leslie and Steven explained the CO2 measurements to me. They measured the alkalinity and DIC (Dissolved Inorganic Carbon), from which concentrations of carbon dioxide, bicarbonate and carbonate can be calculated. The most ingenious I found the measurement of DIC, for which first all ions are converted to carbon dioxide by means of an acid. The resulting liquid is radiated by light with the specific wavelength where carbon dioxide molecules are ionised. Two electrons are measured per molecule. The electric current is integrated by a measurement device. The resulting charge can then be used to calculate the number of mole of carbon dioxide, which is the same as the DIC concentration from the sample.

In the evening there were two lectures; one presented by me about the modelling of trajectories in the ocean, and the other by Gregory about the measurement of concentrations of silicium.

On the fourth day the sampling systems were let down a bit deeper: about one kilometre. An electric connector of the Very Large sampling system seemed to be leaking. After the replacement of a rubber ring there was no more leakage.

In the end we managed to test everything with success. It was interesting to see how the samples were taken, what can go wrong and how some of it is analysed. This gives insight in how difficult it can be to determine the properties of the ocean and how sparse data points are compared to the enormous size of the ocean and the number of available data in models. Also it gives an idea where errors in measurements can arise. In the morning of the fifth day, April 27, we sailed into Scrabster, a harbour on the far North of Scotland. Half a dozen people went off board and new scientists went on board for the cruise to Bermuda.

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