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A day in the water lab

by Henning Waltemathe, 6. 5. 2022

Henning and Martina sampling the Niskin bottles (SO290 – S. Illemann, CC BY 4.0)

Today I would like to give you some insight into the daily routine of our water lab. We are a team of 4 people: Martina, Julia, Mara, and me. We are responsible for sampling seawater that is taken from different depths at several stations during the cruise.The water is taken from Niskin bottles which are mounted to a circular rack and hold 20 litres per bottle. The whole device, with a total of 24 bottles, is lifted into the water on a steel cable and lowered to a few meters above the seabed. In addition, sensors are attached to the rack that measure temperature, pressure, conductivity, oxygen content and turbidity throughout the water column. The deepest place we have sampled here so far is a water depth of 4375 metres. As the device is raised, the open bottles are closed at pre-determined depths so that the water they contain can later be assigned to a precise water depth. This means that a maximum of 24 different water depths can be sampled per station, meaning a maximum volume of 480 litres. After the instrument has been hoisted back on board (the whole procedure with launching and hoisting can take more than 3 hours, depending on the water depth at the station), we are ready to fill our bottles and canisters with water. The volume of the individual samples depends strongly on which parameters are to be measured later. There is anything between 2 millilitres and 10 litres. Some samples are filled directly from the Niskin bottles, others must first pass through a filter to remove any particles. Most of the samples are securely packaged after filling and later analysed in laboratories at the various research institutes involved in our cruise.

Mara working in the water lab (SO290 – J. Warnatz, CC BY 4.0)

Since we take a lot of different water samples for the investigation of various parameters, I will focus on one example here and describe it in more detail.

For the investigation of rare earth elements, we take a filtered sample of about 125 ml, which we will extract the elements from and measure later at the ICBM in Oldenburg. These rare earth elements are metals that are very low in concentration in seawater but show certain distributions and concentration patterns in the world’s oceans. These patterns can provide information about biogeochemical properties of the oceans. For example, rare earth elements may be able to accurately describe and even quantify element inputs to the ocean from land via various transport pathways.

Back to the lab!

After we have filled all our vials and canisters, some samples still need special treatment. To do this, we have been assigned a large laboratory on the ship, where we work only with water samples. Strangely enough, the lab is called dry lab 1, but that should not bother us.
In the lab, some samples are packed ready to be shipped back to the labs onshore, while some others have to go through some pre-processing before further treatment on land. Again, just a quick example from the variety of different samples.
For the analysis of neodymium isotopes, we need to collect 5-10 L of seawater per sample. After filtration, the water is acidified to a pH of 3.5 and pumped over small cartridges. These cartridges contain a resin, which retains certain elements (since neodymium is one of the rare earth elements, the aim is on retaining this group of elements on the cartridges). Other components of the water, particularly the salt, are simply flushed through the cartridge, and ultimately returned to the sea. This process allows us to sample several litres of water without having to lug it home to the lab. Imagine the back ache we’d get bringing all this water home!
And there we go, that would be the end of a day (or night) in the water lab. Although, depending on the depth of the water and the amount of samples, it can take several hours for the sampling and usually we haven’t finished pumping the water over the cartridges before the next batch of samples appears in the lab.
That’s why I will stop here and support my team again. I’m sure they are already waiting for my help!