Oxygen and nutrients

The nutrients of interest are nitrate, silicate and phosphate. The role of these in the ocean is very similar to that of fertilisers used in agriculture and gardening. These nutrients occur naturally in the ocean and are essential for life to grow in the water. They are used by the microscopic plants (phytoplankton) that live in the surface ocean, the part that is lit with sunlight.

We collect seawater from the surface right down to the seafloor, which is up to 6000 metres in some parts of the area where we are working. The seawater is collected with the CTD bottles that can be remotely closed and then brought back on board the ship.

The seawater is then put through a machine called an auto-analyser which mixes chemical reagents with the seawater and turns the nutrients: nitrate, phosphate and silicate, into different colours.

The intensity of the colours formed tells us how much of each nutrient is present in the seawater. All this information is stored on a computer which can then be used for scientific investigation into the concentration, distribution and movement of nutrients throughout the water column.

Autosampler and reagent containers: sampler trays loaded with seawater from the CTD; a needle takes a subsample and mixes it with different reagents

Tray loader with seawater samples and analytical standards which are used as references for working out the nutrient concentration

View of almost a whole nutrient autoanalyser: huge volumes of sea water carry a nutrient 'chemical signature' reflecting prevailing biogeochemical conditions in the surface ocean at the time of water mass formation (in areas such as the Weddell Sea)

This section of the autoanalyser splits into three channels consisting of tubes and coils, where the seawater sample is mixed with chemical reagents, helped by the addition of tiny bubbles at intervals

The chemical reactions generate coloured light, the intensity of which is proportional to the concentration of a given nutrient; the colour light absorbance is detected and recorded on the computer

Organisations involved in Andrex (Antarctic Deep Water Rates of Export)