JC010: Mud volcanoes and submarine canyons


Cruise diary

Day 14: Friday 25 May 2007
Position: Latitude 35º, Longitude 8º, Bearing 235º
Weather: Flat calm, sunny

Gillian writes:

"It is so calm the sea was like glass today. The sun reflecting on the surface at dawn was spectacular.

Today the geochemists have been carrying on with their analysis so we thought this is a good opportunity to tell you a bit about just what it is that they do.

Many of you will have done titrations at school and the technique that the chemists use here is based on that, but the equipment that they use is designed to work with very small quantities ( 0.5 microlitres ) and it is extremely accurate. The burette is inside the machine and it is driven electronically and gives a digital read out. This is used to measure alkalinity. Another technique you may have used at school is colorimetry. This involves the compounds that the chemists are analysing, such as ammonium and hydrogen sulphide, reacting to produce coloured compounds. These are placed in the colorimeter and the strength of the colour is a measure of the concentration of the ammonium and hydrogen sulphide in seawater. This is interesting because they can then compare the 'normal' seawater with seawater around a mud volcano. Again many of you will have studied chromatography in school where you put dyes on a piece of chromatography paper and let them run and you see them separate out. Darryl (one of the geochemists on board) uses a chromatography machine that works on the same principal and allows him to see how seawater and mud volcano fluids vary. Eduard explains this in the short video clip below. The methane is measured using a complex piece of kit built at Southampton University especially for the job, called the vacuum degassing system and a gas chromatogram. It measures the amount of gas given off and then is able to determine whether the gas comes from deep, deep within the earth's crust or whether it is from bacteria in the sediment.

These machines are very complex in the operation, but the readings that they give enable scientists to make sense of what is going on beneath the crust. In turn this explains why the life on it is as it is..."

Eduard writes:

"Isis is still under the water, examining the crater of the Carlos Ribeiro mud volcano, and it will be working until tomorrow early morning. It has been doing a video transect, now it is doing bathymetry and after mapping the crater the Isis is going to sample water with the aqualab. Yesterday night, while the Isis was doing the video transect, we could see loads of sponge, holothurian, different kind of fishes and a big octopus! It wasn’t scared when it saw the Isis - instead of swimming away, it faced us.

A Holothurian (or sea cucumber) is a kind of echinoderm and a relative of the starfish, with an elongated main part. When we were in the van, hundreds of them suddenly appeared. It was amazing! Some of them are able to swim and we could see them suspended half a meter above the seabed! You can find holothurians all over the deep-sea world. In some parts of Asia, like Japan, they eat them! As soon as we can, we will send some photos. The scientists record all the images into digital data. After each session, they have to edit all the interesting frames in the computer. It takes a lot of time, because they have hours and hours recorded to work on.

Tonight we have been watching the sunset from the Forecastle deck (at the front of the ship), the perfect place for a short break. The sunset was magnificent today!"

Dawn breaks calm and still in the Gulf of Cadiz...

...with a matching sunset
at the end of the day

Something about the chromatograph amuses Belinda

Titration apparatus

Vacuum degassing system

Gas chromatography

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