One of the main parts of our project is to try to understand how the chemistry of the Arctic Ocean varies and how it may respond to climate change. To do this we need to collect a lot of water from the shallow waters all the way to the ocean abyss.
How do we do that? The main way to collect water is from a rosette which holds 24 x 20 litre bottles, on the rosette there is also an instrument called a CTD which keeps track of the depth as the rosette descends. It also can measure the amount of salt in the water, the temperature and there are sensors to measure things such as the oxygen concentration.
When we arrive “on station” (at the location we want to sample), the rosette starts to go down in the water. The rosette is attached to a cable which is controlled by the crew on the deck of the ship. The cable is released slowly until the rosette is near the bottom of the sea (sometimes the depth is up to 3500 metres).
Each portion of the water column is different in the amount of oxygen, temperature, amount of salt etc. The different portions of the water column are called “water masses”. The CTD is linked to a computer on board that we can watch while the rosette is going down the water. On its way down, the CTD measures the temperature, oxygen etc. and when the rosette is at the bottom, we know the characteristics of the whole water column (from the surface to the bottom). We use that to decide which depth we want to sample.
When we know which depth we want to have water from, the rosette is slowly brought back up. When the rosette is at a depth we want to sample, we stop the rosette and close one of the bottles. This bottle will keep water from this specific depth until the surface. It can take up to 3 hours for the rosette to go down to the bottom of the sea and back up at the surface. When the rosette is brought back on board of the ship, each bottle contains water from different depth.
We then go around the rosette, open each bottle and take the water from it in smaller containers. We have one container for each of the measurements we will do: the dissolved nutrients (carbon and nitrogen) and the particulate organic matter.
Celeste, Robyn and Camille sampling from the rosette.
What do we do with this water?
Once we have collected the water we take it through to the lab where all of the fun and filtering happens! Everything in our sampling room is secured to the work benches, so that when the ship moves, your filtration rig stays in place.
We filter the water for dissolved nutrients (carbon and nitrogen) and for particulate organic matter (POM). The water is run through different filtration rigs depending on what we want to measure.
The filtering can take different amounts of time, for example the POM takes 8 hours! As you can imagine, we sometimes need some music to help us power through the longer shifts…when you’ve been up for 12 hours working, ABBA is definitely the go to playlist.
Robyn filtering for the dissolved nutrient samples.
Camille sampling for particulate organic matter.
This is what the particulate organic matter looks like on a filter, after 8 hours of filtering!
Some bottles are frozen to temperatures as low as -80 and others are kept in the dark.
For some samples, you need to stop biological activity (i.e. small animals in the water from eating and using your nutrients). To achieve this, chemicals are added to the samples.
Once we have prepared and stored all of our samples, they are transported back to the UK in the ship and then we take them back to the lab to analyse.