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Field science: water sampling

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“There’s no point in doing oceanography if you don’t know what the temperature and salinity are doing. It sets the scene for all the other measurements and samples you take,” remarks Dr Helen Findlay.

We are out in the boat again on Kongsfjorden, the inlet running from the Atlantic Ocean to the Kongsbreen glacier and edging past the science village of Ny Ålesund.

It is easy to forget that the ocean is not just a massive bathtub, but contains different layers of water with different properties at different depths. Internal waves ripple through it and internal rivers run through our seas and oceans. There are two main instruments used for water sampling and they allow scientists to map the water column.

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The first instrument is a niskin bottle. To the untrained eye, it looks like a length of drainpipe with elasticated ends. The niskin bottle has been used for sampling in the polar waters since 1910, when it was designed by Fritjof Nansen and Otto Sverdrup.

The bottle is lowered into the cold dark waters of the fjord on the winch, ends held back, to the desired sampling depth. At each waypoint along the fjord, Helen would take samples at a variety of depths, surface, 15 metres, 25 metres, etc. When the niskin bottle is at the desired depth, a small brass weight, known as a ‘messenger’ is sent down the wire to snap the ends closed and capture a sample of seawater at specific depths.

This is then drawn back to the surface and carefully decanted into obsessively labelled bottles. Helen is studying the carbonate and nutrient (e.g. nitrates and phosphates) content of the water samples. Helen adds mercuric chloride to the samples, which kills any microorganisms, to ensure that the levels of carbonate do not change after sampling has take place.

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The other instrument that is used is a CTD, standing for Conductivity, Temperature and Depth. Again lowered over the side of the boat using a winch, the CTD is used to create a profile of the water column and its important physical properties.

These samples and data sets will then be analysed later to give Helen and the team a better understanding of the waters of Kongsfjorden.

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