Category: OD Nature

28 June 2023 – Three down, two to go! As if the Van Veen grab, the box corer and the GEMAX corer don’t provide the DEHEAT-team with enough sediment samples to learn to understand the bottom of Hvalfjördur and the biogeochemical processes taking place in it, the scientists are sending two additional types of devices to the bottom to collect even more sediments.

The first is the long gravity corer, that essentially consists of a narrow corer of 3m in which a sampling tube is fitted – or two such corers and tubes combined, totaling 6m – and a huge weight to drive the corer into the seafloor (hence ‘gravity’ corer). This way, much deeper sediment layers are cut than with the other techniques, with deeper meaning older. The long cores allow the sedimentological history of the seabed to be reconstructed and to unravel a host of secrets from the past. In the case of DEHEAT and of the biogeochemists on board, this is obviously done with attention to how silicate weathering has evolved over time here, and how historical changes can be linked to climate-relevant processes.

Christian März, Professor for General Geology at the University of Bonn, is especially interested in the deeper part of the sediments, and therefore depends on the long cores. By studying these, he can determine how the composition of the sediment changed over time and how these changes affected the cycling of essential elements like carbon, metals and nutrients in the seafloor. By studying past environments from the sedimentary records, climate change signals can also be extracted.

“It is also exciting to dive deeper into the topic of silicate weathering, a new and quite hip topic due to the need to stop and reverse global warming. Through this link, my colleague Katrin Wagner and I got offered the opportunity to join the expedition with RV Belgica in Iceland as collaboration partners of the DEHEAT project. As such, we bring in our expertise both for the benefit of our and the DEHEAT research” Christian explains.

However, deploying and retrieving the long gravity corer is anything but an easy task. And once in the water, the actual sampling of the bottom does not prove to be easy either. Indeed, the multi-purpose and interdisciplinary RV Belgica is not perfectly equipped for this particular type of sampling. It takes a lot of inventiveness and advancing insight to get the procedure right, but the highly motivated crew succeeds and regularly delivers usable ‘long cores’ to the scientists.

Christian: “The long gravity corer cannot be deployed over the sides of RV Belgica, so this has to be done from the stern. If swell causes the amplitude of the movement of the stern to be bigger than the accuracy with which the position of the corer in relation to the depth of the seabed is known, it is nearly impossible to successfully apply this method. We sometimes have to try several times but in the end manage to secure good cores thanks to the crew”. He adds laughingly: “This is why I like working in the central arctic so much. There, the ice prevents the ship from moving and allows us to work more accurately”.

Finally, there is a fifth way by which sediment is brought to the surface during the DEHEAT cruise: the benthic lander. However, it would be irreverent to wear this unit down as a simple ground grabber. After all, the lander does much more than that. It is a platform that is sent down in the deep to take measurements on the seafloor itself, and that is equipped with so-called ‘benthic flux chambers’ that measure the flow of substances between the seafloor and the water above it. It stays on the seafloor for one or several days while the DEHEAT-scientists proceed and sample at another station, and carries out the pre-programmed actions while storing the resulting data in a battery-driven data logger.

The benthic lander that is used during the DEHEAT-expedition belongs to the University of Gothenburg,  Sweden, that employs a true benthic lander guru in the form of Mikhael Kononets. It is almost inconceivable that the lander would be deployed without Mikhael being present to oversee the operation, so the Royal Belgian Institute of Natural Sciences arranged a contract for him for the duration of the RV Belgica adventure in Iceland, as well as for the subsequent expedition in Greenland. He boarded in Galway, Ireland, and was continuously engaged with the lander throughout the transit to Iceland as well as during the two-day stay in Reykjavik. Mikhael and the lander seem intertwined, and he did not even set foot on Icelandic soil but kept busy with making sure that the lander is fully ready for its duties on the RV Belgica. “It’s only concrete, that’s the same everywhere, isn’t it?” he jests.

There is some work involved in deploying the lander from RV Belgica, and especially in retrieving it. Mikhael explains how this works: “Deploying the lander is not so much the problem. It can be lifted over the side, after which ballast causes it to sink to the seabed. Old pieces of railway track, which were donated to us by the Swedish company Stena Recycling, are used as ballast in this case. After the lander has done its job, we activate the decoupling mechanism with an acoustic signal via a hydrophone, whereupon the styrofoam-filled compartments cause it to rise back to the surface. The railway tracks remain behind, which is not a problem as primary production in the sea is limited by the availability of iron”.

Only then does the hardest work begin, getting the lander back on board. Mikhael: “First, the floating lander must be spotted. We usually know its position very accurately, but if we cannot see it immediately – due to wave action, for example – we can still determine in which direction to look using a simple radio signal. Once found, the lander is then carefully towed by RHIB (rigid-hulled inflatable boat) to near the stern of the RV Belgica, from where he can then be hoisted on board. The time elapsing during the calling and ascent of the lander through the water column can sometimes be nerve-wracking … after all, there are known cases of landers lost for eternity …”.

For launching this wide variety of sampling equipment, for the actual sampling of the water column and the bottom, and for retrieving the equipment again, it is obviously very important that the platform on which these operations take place is very stable and remains very accurate on site. For the first, the RV Belgica is indeed a very stable vessel but wind and wave action are also important and one also depends on the swell. For the second, the so-called Dynamic positioning system comes into play. Dynamic positioning is a computer-controlled system to automatically maintain a vessel’s position and heading by using its own propellers and thrusters. The DEHEAT-team is blessed: all sampling is proceeding as planned in Hvalfjördur thanks to favourable conditions and the RV Belgica’s Dynamic Positioning. Fingers crossed that this will continue to be the case later on the continental shelf.

Now, don’t get us wrong, the soil sampling techniques mentioned are not only used on the day they are described in this blog but are part of the routine of every day. The same goes for the CTD reviewed earlier, and for many of the operations and analyses that will follow.

And the fjord? It remains its picturesque self!

27 June 2023 – How many ways can one think of to bring mud from the seabed to the surface? As many as five are applied during the DEHEAT campaign with RV Belgica, all designed in different ways but with one common goal: bringing samples of the precious mud, its inhabitants and chemical gradients, to the scientists without them having to get wet! However, avoiding them getting dirty cannot be guaranteed! Admittedly, it is better to speak of ‘sediment’ instead of mud, because technically it is not always mud that is brought to the surface. Just as one water was not the other, neither is one sediment the other.

Let’s start with the simplest low-tech method, which is usually the first sediment sampler deployed on any new sampling station during the DEHEAT campaign: the Van Veen grab (or simply the Van Veen). Once the CTD is back on board, that is. This tool is nothing more than a clamshell bucket made of stainless steel that is spread open like scissors while it is let down through the water column. The locking mechanism is released when it touches the sea bottom, making the bucket halves close and grab a sediment sample when the device is pulled back upwards.

In the extended sampling scheme, a box corer is usually sent towards the seafloor when the Van Veen grabbing has been completed. This can be done once or multiple times, depending on the sampling needs. From a technical perspective, the box corer is also a rather simple sediment coring device, essentially consisting of a cylindrical core that relies on a weight to aid the cylinder to penetrate into the bottom and on a spade that seals the core from below to prevent the sample from being lost when the unit is lifted back to the surface.

Next on the programme comes deploying the GEMAX corer. This one looks a bit like a double torpedo with wings (see photo, showing the device before it is lowered to the seafloor) where tubular sampling containers are inserted into the two cores to be taken out – hopefully filled with sediment – after retrieval.

Unlike the Van Veen grab and the box corer, the GEMAX is not deployed just once or a couple of times at every sampling station, but up to 22 cores are collected per location.

Per Hall, marine biogeochemist and emeritus professor at the University of Gothenburg, explains: “The GEMAX takes more undisturbed cores and therefore delivers a more representative sediment sample than for example the box corer. The latter disturbs the sediment more, for several reasons. One is that it has a very big ‘bow wave’ which may blow away particles from the sediment surface. Also, the sediment within the box may be more disturbed, there may be cracks in it, there may be water coming between the box wall and the sediment. That is often fine, like if you’re going for fauna samples, but if you want undisturbed chemical gradients in your cores as is needed for many of the DEHEAT biogeochemical analyses, the GEMAX is a far better choice. So, the choice of corer all depends on the purpose of your sampling.”

Per is a senior academic who is not averse to dirty hands. “Although I am officially retired, I still do part-time research because I remain interested in it and excited about it. Today, I am participating in this expedition on invitation of Sebastiaan, where I try to bring my expertise in throughout the entire chain from the practical aspects of the sampling to the discussions on the data“.

Saheed Puthan Purayil of the Royal Belgian Institute of Natural Sciences helps Per with the different sediment corers. He is a PhD in physical oceanography, and has extensive experience in ocean research, forecasting and modelling. But rolling up his sleeves was less of a part of these experiences.

“I have been a part of many scientific expeditions at sea, and in some cases I had the position of chief scientist, but it is the first time that I am actually helping with taking sediment cores. I find it extraordinary to see how the cores are processed after we hand them over to other scientists, and how some data are already appearing during the expedition” he says.

Saheed clearly enjoys being part of the DEHEAT expedition: “It’s also a fun and engaging expedition, with scientists of so many different fields of expertise, institutes and nationalities, and a wonderful ship and crew. And everybody is very friendly!”

All the abovementioned sediment corers, as well as the CTD, are deployed over the starboard side of RV Belgica, using a crane and winch specially installed for deploying such instruments.

The CTD actually has it’s own hangar and deployment system, as you don’t want the sediments flying around contaminating the valuable water samples. Just kidding! Of course, the sediments are also handled with great care. But when hosing down the corers between sampling sessions (as even residual sediments from one sampling must not affect the next) it is not inconceivable that some sediment could get onto the CTD-rosette or into the water samples. And for the scientists carrying out the accurate and clean CTD sampling, it is also more correct and pleasant work in bad weather conditions.

Talking about the weather, we were warned that the weather in Iceland can take any form in summer too. Today we witnessed that, with alternating sunshine, clouds, fog, a gust of rain and even a flake of snow. But Hvalfjördur remained as dramatically beautiful in all these conditions!

26 June 2023 – There is pleasant excitement on the RV Belgica this morning, as the ship leaves Reykjavik harbour and steams to the first sampling station. No far journey ahead, as the first days of the expedition will be spent in a fjord just north of the Icelandic capital. The fjord in question is the Hvalfjördur, literally translated as the ‘whale fjord’. It only takes less than two hours to arrive at station HF3, which gets the scoop of being the first to be sampled. That first sampling is always a crucial moment, as it is definitely better for morale to start with a success. However, only one thing is certain at this point: the weather will certainly not be a killjoy! The water is calm, the wind absent, and there is pleasant sunshine.

The DEHEAT campaign kicks off with a CTD deployment, which will become the regular start of activities at each sampling site. CTD stands for conductivity, temperature and depth, parameters that are measured by sensors that are incorporated in a construction that further includes 24 so-called Niskin bottles arranged in a rosette. For simplicity, we refer to the whole thing simply as ‘CTD’.

The CTD-construction is an essential oceanography instrument. As the CTD descends through the water column to just above the bottom, the depth and the changes in temperature, salinity and oxygen content of the water can be monitored in real time on a computer screen. Depending on the course of these parameters, the scientists will decide at which depths water samples will be taken. That is where the Niskin bottles come in, as they can be closed remotely one by one with a simple mouse click. This is done during the rosette’s journey back to the surface.

During the first trip of the CTD to the bottom and back up, the wet lab where the computer on which the CTD parameters are monitored was particularly crowded. Everyone wanted to personally witness the very first data that appeared during the DEHEAT expedition. In the following days, this moment will be much less attended. Of course, this has nothing to do with a loss of interest but is entirely due to the fact that during the very first CTD, no other activities had yet started. Things will be very different at subsequent stations, and the timing of activity from different scientists will also be increasingly divergent as a result.

Later, it will therefore mainly be some regular faces who will be present at every CTD, make the decisions on water sampling and close the Niskin bottles. Besides DEHEAT chief scientist Sebastiaan van de Velde, the permanent CTD team consists of Kate, Lei and Felipe. It is also they who will eventually sample the contents of the Niskin bottles in different ways for different purposes.

A decent administration is involved as everyone on board wants their share of the water, and one water turns out not to be the other … There is a need to collect samples for determining alkalinity, dissolved inorganic carbon, nutrients, Silicium, metals, oxygen, Magnesium & Strontium, salinity, … and all of these samples are needed in different volumes, need to be stored in different recipients, require different processing and need to be brought to different places on the ship. To complicate matters further, some samples have to be collected only in the fjord, or later only on the shelf, or only at certain depths, and various expedition participants come with large or even larger bottles to get their share of water as well …

The important task of keeping record, not only for CTD sampling but for just about all samples taken during the expedition, falls to Kate Hendry. Kate is an ocean climate scientist, chemical oceanographer or biogeochemist at the British Antarctic survey. She is part of the science and steering groups of DEHEAT, and has also been designated as the expedition’s second chief scientist.

Kate explains what that means: “The co-chief scientist position involves being there as a sanity check and a sounding board for the chief scientist. On an expedition like this, there is a lot to think about and keep an eye on, and there are a lot of important decisions to be made. My task is to come up with ideas, suggestions, alternatives, solutions to any problems that may arise. But to be honest, Sebastiaan is doing such a great job, so it’s not been too bad for me at all, it’s all running very smoothly”.

On the task of keeping track of all that’s going on, she adds: “Next to the science, I’m focusing on the data management, looking after the paperwork, making sure everything is archived. The last thing you want is some critical paperwork going missing, so I make sure everything is scanned and archived. This sometimes turns out to be even useful months or years after a cruise, when something confuses or puzzles people, creating a need to go back to the vital original logs”.

Back to the CTD sampling now. Felipe Sales de Freitas, chemical/geochemical oceanographer and postdoctoral researcher at the Université Libre de Bruxelles, is directly involved in the DEHEAT project and takes care of what can be considered the ‘small volume CTD sampling’ for a whole range of goals, most of which require the water from the Niskin bottles to be filtered.

“But first we have to go through the sacred ritual of rinsing every recipient or sampling tool three times with the actual water that is going to be sampled” he laughingly explains. “Next, we squeeze water through syringes and filters until our thumbs are completely cramped”.

Felipe further explains his role in the DEHEAT Belgica expedition as follows: “In this expedition, I am basically an extra pair of hands in various sampling actions because of my experience in field sampling and analysis. Later on, I will use a lot of the output data of the sediment coring and water analysis for the DEHEAT geochemical modelling”.

Lei Chou, meanwhile, drags larger containers back and forth between the Niskin bottles and a more sophisticated filter setup that she provided herself, that is better suited to filtering larger volumes. She is a marine biogeochemist and emeritus professor of the Université Libre de Bruxelles and remains active and connected to both research and training of students.

Lei had very little time to prepare for the DEHEAT expedition but is making the most of it: “I was offered a berth on RV Belgica only weeks before the start of the expedition when a place suddenly opened due to the cancellation of another participant. I had to move quickly, sending two suitcases of equipment to Reykjavik as the Belgica had already left its home port of Zeebruges. After all, I want to take the opportunity to collect additional samples for suspended matter content, nutrients, metals and chlorophyll to complement the already very ambitious DEHEAT plan”.

We can rest assured that Icelandic seawater will hold far fewer secrets after the analysis of the DEHEAT samples.