The marine chemist gives an example: “Of course, we are very interested in where the carbon goes in the geosystem. There is a constant exchange of gases between the ocean and the atmosphere, including that of carbon dioxide and other climate-relevant gases like methane and oxides of nitrogen, but also of so-called trace gases containing halogens, which are often harmful to the environment. In order to make more accurate projections concerning the climate in the Arctic using mathematical models, we need to understand how these gas exchanges work in detail.” MOSAiC experts from the Biogeochemistry (BGC) Team continually monitored these gases and other important chemical compounds in the water – and they did so throughout the entire annual cycle that the Polarstern drifted across the Arctic. “The exchange of carbon dioxide between atmosphere and ocean is strongly limited by the amount of ice in the ocean. Ultimately, like a lid, the ice is a barrier to gas exchange. Thus, it is important to take a look into the complex interactions between the ice and seawater. It is crucial to study how the amount of sea ice covering the ocean changes and how the exchange between ocean and atmosphere varies during the year.”
“It is also crucial for our department to understand how life in and under the ice can change over time”, says Koch. “We try to gain a better understanding of the parts that microorganisms and algae play in chemical processes; after all, both are major ‘gas producers’. This is another significant parameter for the binding of carbon dioxide via photosynthesis.” Moreover, the biogeochemical system is closely linked to the Arctic ecosystem.
Liquid handling far below zero
Water samples are obtained, for example, through ice boreholes, explains Koch. "For my area for research, the water column is the decisive factor. We tried to sample the underlying water with water samplers through boreholes in the ice. During most of the expedition this worked well, but in one section of the journey it didn't work at all because of the extreme ice situation, which meant that it was practically impossible to keep a hole large enough to sample the water column properly.” The scientists had a special heated area on the ice called Ocean City. “There we tried to compensate a little bit for the extreme cold. Of course, working on the ice is completely different from simply using the ship's crane with a large water rosette.” The water rosette is a metal frame with 24 hanging water bottles, says Koch. “These are let into the water with the help of a cable and we were able to look at physico-chemical data from the water column and then ‘catch’ the corresponding water at a defined depth.”
When weighing does not work, it's time for the pipette
During the expedition itself, when being outside on the ice, pipetting would not work at all, says Koch. “Where even the pumps will freeze, there are a lot of things that do not work.” Most chemical and biological work has to be done in the home laboratory, either at the Alfred Wegener Institute or at the labs of the international partners. “But what we did on board is nutrient analytics. We wanted to know which nutrients are available in the water column or in the ice, i.e. nitrate, phosphate, silicate as important compounds of life. For this purpose, we had an auto-analyzer on board, a flow injection system. And we also pipetted on board, of course. Since it is not possible to weigh anything when on board of a ship that is pushed around in an ice flow, pipetting is the preferred technique in many situations. To enable precise work, we had pre-weighed standards for nutrient analytics so that exact volumes could be obtained. And this was and is only possible with a good volumetric measurement.”
A salty challenge
"What's really annoying about the sea is the salt," says Koch, smiling. “Due to the salt, some things in marine research are eliminated that could otherwise be put to good use. This applies, for example, to different types of syringes. Syringes with glass plungers simply don't work there. After using them once or twice, salt crystallizes out and the glass bulb is stuck. Even with plastic syringes this can be very annoying, they do not work properly in this environment.” As salt is a problem in many applications, this could affect direct displacement pipettes as well, explains the marine chemist. “Thus, we use air cushion pipettes so that the salt does not come into contact with the plunger. Metal on pipettes can be a problem as well, because it is attacked by the salt. Therefore, we generally use plastic and glas pipettes.”
Sample handling is a huge issue
Since many measuring instruments are sensitive to vibration, analyses often had to be carried out afterwards, in the home laboratory. This posed further challenges for the conservation of samples during the year-long mission. “Any scientist affected by this had to conduct diligent studies to determine whether the analyte is contained in the vial or not. This is one of the most elaborate tests when developing methods in the run-up to the scientific mission and it is how it is done in chemistry.” In the specific case of MOSAiC, there were many samples that had to be kept for the entire mission. Since there was only limited space, the sample volumes had to be rather small. “This starts with DNA extracts and extends to water samples of perhaps half a liter. The famous ‘Eppi’ Tube is the most common sample container in the DNA field, in organic chemistry we rather use pre-combusted glassware. For some tests we even have the confidence to use a high-density PE or similar materials. Even Teflon is used from time to time. Leaching effects are of course always a huge topic in organic chemistry.”
Limits of automation
Collecting samples is done manually, there is simply no other way, says Koch. “Thus we did not use autosamplers – but we tried to automate other tasks wherever possible, e.g. the automated solid-phase extraction. We had considered taking it with us at the beginning. However, after extensive testing in the run-up to the mission, we realized that the device was so complex that we could not expect it to be used by five teams over the entire journey. So, we finally decided to perform the solid-phase extraction manually.”
Many challenges in the Arctic are reminiscent of those in space
"We had to conduct an enormous number of different studies, including those of our international partners," says Koch. And space on board is limited, albeit on a different scale than in the International Space Station. "We had the opportunity to travel with fifty scientists on board, but otherwise there were many parallels to space travel. As in orbit, the limitation of space and time at MOSAiC was a huge challenge". And the polar researchers solved the problem in a very similar way to the astronauts. "We carried out very extensive training in advance to enable them to collect samples for other colleagues as well."
Also similar to what it is like on the ISS, the regular crew changes in the Arctic were a huge challenge. “We had five different teams on board who had to sample the same parameters exactly in the same way. We therefore spent a great deal of time and effort in advance to align methods and train them in workshops. That was the challenge. Whether we really succeeded in doing so, we'll see in retrospect from the data. This can be done through statistical tests. Of course, there are also control checks according to certified international standards on board. In the end, we will run statistics with the processing person as a test parameter.”
And there is another similarity: “When going on an expedition like this, always think of enough replacement materials to service pipettes and other equipment.” Making sure that everything needed was on board required a lot of experience - and a good deal of oversubscribing, i.e. packing more material than you plan to take samples. This trip was quite a hardware hassle, says Koch. “You have to think about what could be broken - and take the stuff with you to fix it. Apart from that, we also had great people on board, electricians and mechanics who could help with repairs.”
Now the actual lab work begins
He adds: “We are now tremendously busy merging the metadata of the samples and distributing the samples all over the world. For my area of research, the scientific work is just about to begin. Other research divisions have already collected many results, especially with regard to climate change. On a normal expedition, perhaps a greater share of analysis would have been done on site, but MOSAiC was mainly about collecting samples and measuring data. Roughly speaking, we have collected about 20,000 samples, which now have to be evaluated.”
Lessons to be learned
Although many of the specific challenges of the MOSAiC mission may seem far away in temperate latitudes and on solid ground, there are some interesting things worth learning from the research scientists' experiences for daily laboratory work.
- All experiments should be thoroughly thought through before starting the mission in order to have all necessary reagents and much-needed equipment on board - including any necessary replacements.
- Where spare parts and service technicians are not always available, researchers really have to rely on their equipment.
- In order to be able to estimate the expected lifecycle of the equipment for procurement, data from the reliability tests in the Application Notes can provide valuable reference points.
- Eppendorf experts are available to assist scientists with their experience when planning laboratories or research missions.
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