I have had the privilege to sail twice on the JOIDES Resolution, with this being my second cruise, Expedition 402 Tyrrhenian Continent-Ocean Transition. The first time was with Expedition 393: South Atlantic Transect II. We aimed to study the age of the oceanic crust as we moved away from the mid-Atlantic ridge toward South America. You can see the expedition summary here.
At the time I had very little understanding of rocks and sediment besides what my oceanography class in college provided me. Most of my academic career was focused on the biology of organisms, so when I thought of rocks I thought of how they provided shelter and structure for the living things that I studied. For instance, rocks provided a hard surface for corals and algae to root themselves and sediment provided hiding spots for bottom dwelling fish. After a few days on Expedition 393, I learned that rocks and sediment can hold the history of our atmosphere, the history of our oceans, and the history of catastrophic events (big or small).
The rocks and sediment on both expeditions have been extraordinarily different. I cannot say that I have seen a similar core between the two, which makes sense because we are in drastically different areas. But again, I had the genuine thought, what could be different about the seafloor from one place to another.
Each expedition has different goals, and different operation expectations, however the methods we use to drill, make thin sections, make p-wave velocity measurements, and more tends to be relatively the same give or take some modifications. For example, thin sections can only be done by taking a small piece of hard rock, cut a thing slice from the top, then polish it down to the thickness of a hair strand. That process does not change because we found a rock in a different ocean. As someone who was returning to the JOIDES Resolution, I envisioned seeing similar gray rocks with some dark grays and browns, I envisioned seeing sediment that followed the color range of chocolates in a chocolatier shop. I figured I was going to be learning about the ocean floor from a different perspective guided by the different expedition objectives. Immediately, I was very wrong and it was thrilling. As Phillipe Pezard, our Downhole specialist, said on one of our first days: “I am a kid in a candy shop”. The ship is a candy shop and the scientists are the local kids who just got their weekly allowance.
Sediment in the Tyrrhenian Sea did not look the same as that of in the South Atlantic, nor did it seem to act the same way when we drilled into the seafloor in both locations.
As someone who does not immerse themselves in geology every day, I still was able to follow the science party as they explained their research goals and expectations from the scientific prospectus in the weeks leading up to expedition 402. Rationally it felt straightforward to understand that under different circumstances like temperature and pressure sediment and rocks react in certain ways. It felt straightforward to understand that these materials will undergo change, erosion, weathering, layering and more. But once I saw the actual cores a foot away from my face, it was a whole other beast. That is the value of field work and that is the value of this ship. You cannot learn more about this planet if you do not have access to it.
As I reflected on my two expedition experiences and saw the science crew experience a range of emotions as new cores were collected, I decided to go around and ask some people who have been on multiple expeditions for their perspectives.
“What has surprised you about the rocks and sediment you have seen across expeditions?”
Alejandro has sailed on 8 expeditions (or 6, he wasn’t entirely sure) and is sailing as the Physical Properties Lab Specialist. He is most surprised by the homogeneity (the sameness) and the gradual change in characteristics of the cores from the bigger oceans. When he was in the Pacific it took a few cores before you started to see a huge color change or texture change, while in the shallower basins the cores tend to be more heterogenous (varied) and have more rapid changes to their features. It always keeps him asking why.
Emily Estes has sailed on 4 expeditions with the JOIDES Resolution and is the current Expedition Project Manager. She is surprised that even when we have the prospectus identifying everything that we expect and understand to be in the area, we still find something different. Especially when the data in the prospectus is based on previous drilling sites in the area, one would think the core would bring few surprises. Though she does not think of these moments as bad surprises, but as opportunities to ask more questions. Most of her work and expeditions have been in larger oceanic basins where there are similar features throughout multiple cores before it starts to change, which is not the case for the shallower basins like the Tyrrhenian Sea.
Kevin Grigar has sailed on 24 expeditions and is the Operations Superintendent. Though his role is to check how well the cores are coming out to help determine with SIEM Offshore what could change about the drilling operations and procedures, he still gives the cores a look. What surprises him is the change in formations and color throughout the cores, sometimes within the same core and sometimes it is after a few ones. Either way he is amazed, and loves how pretty the changes can look.
James Kowalski has sailed on 3 expeditions and is sailing as the ship curator. He is surprised by the laminations (layering that happens in sedimentary rocks) and features that disappear quickly between cores. He finds that each core is so different and rarely sees similarity across expeditions. The variety is something that he enjoys and it keeps him on his toes.
Hearing their responses made me think of the cycle of scientific thinking (https://www.youtube.com/watch?v=j12BBcKSgEQ) and what one of our co-chiefs, Nevio Zitellini, said the other day “We start this expedition with a question, and we end this expedition with more questions.”
As we settle into week 3 of Expedition 402, I enter it even more consumed by two notions. First, that we still have so much to learn, and secondly, it seems that when I ask “how could rocks and sediment from one ocean to another be different” it is a question that scientists and the public, alike, share.
Welcome to Cádiz
When we arrived in Cádiz in April, we knew that we would be spending the next months working on an experiment about underwater soundscapes. What we did not yet know was how much of our time would be spent carrying equipment through the city, rebuilding experimental frames, solving technical problems and trying to convince various pieces of equipment not to end up at the bottom of the Atlantic.
Cádiz itself was a pretty good and beautiful place to start.
The city is located at the very tip of a narrow peninsula and is surrounded by the Atlantic on almost all sides. There are beaches almost everywhere, small streets leading through the old town, the harbour with its many boats and plenty of places where you can simply sit down and watch the sea. It did not take us long to understand why Cádiz is sometimes called La Tacita de Plata, the Silver Cup.
Our first evening was still fairly relaxed. After arriving and settling in, we went out together for a drink and explored a little bit of the city. It was a good introduction to our new home. The next morning, however, the relaxed part was over and GAME 2026 officially began for us.
Our project focuses on how underwater soundscapes may influence the colonization of hard surfaces by marine sessile organisms. To investigate this, we used standardized PVC settlement panels mounted on experimental frames and exposed them to different underwater soundscapes.
Over the course of the experiment, we monitored which organisms settle on the panels and checked whether the developing communities differ between the different acoustic conditions. The panels themselves were only 15 x 15 cm in size, but the frames, which were holding them while they were underwater, were much larger and required quite a bit of construction and preparation.
So, before we could investigate anything, however, we had to build everything.
Building the experiment
The first weeks in Cádiz were all about getting the experiment ready. Before the panels could go into the water, we had to prepare the equipment, rebuild the experimental frames and organize everything needed for the different parts of the experiment. Our setup consisted of large rectangular frames made from PVC pipes that carried the 15 x 15 cm settlement panels while they were in the water. In addition to this, we had speakers for the sound playbacks and ropes, buoys and weights that kept everything in position.
Although, there were frames left from a previous GAME project that was done in Cádiz, we decided to build new ones, which meant sourcing new material, cutting and assembling PVC pipes, preparing the panels and putting the different parts of the setup together. Some materials were bought locally, while others had to be ordered. This also resulted in one of our first small fieldwork adventures: transporting several metres of PVC pipes in a public transport bus through Cádiz was not exactly an everyday activity. We did not have a car at the time, and the large hardware store, where we bought some of the material, was quite far away, so getting everything back to Cádiz meant taking several buses while carrying long PVC pipes through crowded streets and vehicles. We bumped into things more than once, attracted a fair amount of attention and quickly realized that carrying several metres of PVC through a busy city is not as easy as it sounds. At one point, the combination of researchers, long PVC pipes and a local hardware store became what we jokingly refer to as the “Bus Hardware Store” episode.
Building the frames also taught us quite quickly that fieldwork rarely goes exactly according to plan. Some parts required a bit of improvisation and technical problem-solving, and when we reached a particularly stubborn technical issue, we even called Liam’s father in Germany for some additional advice. Although he was not directly involved in the project, his background in mechanical engineering and his experience with practical technical problems made him a useful person to call when we needed another perspective. A video call across Europe was not exactly part of the original plan, but it turned out to be a useful addition to our fieldwork toolkit.
At the same time as we worked on the set up, we were preparing the recordings of natural underwater soundscapes that would later be used for the experiment. For this, we built a deployment system consisting of a concrete-filled bucket, a wooden pole and a HydroMoth attached to the pole. The idea was simple: the heavy bucket keeps the structure stable on the seafloor, while the hydrophone records the surrounding natural soundscape above it. The practical part was considerably less simple. Several heavy loads of concrete had to be transported through Cádiz, and once the equipment reached the beach, getting the concrete-filled bucket into position was another workout altogether. We used a two-wheeled hand truck to move the heavy bucket across the beach and then into the shallow water. From there, we worked our way out by snorkeling and swimming, carrying and guiding the setup into position. The water was no more than about two metres deep, so there was no need for a boat.
The setup may have looked a little unconventional, but it was based on the plans we deleoped for recording natural soundscapes during the preparative course in March. After plenty of cutting, drilling, tying, carrying and assembling, the first major pieces of the project were finally ready. The frames were taking shape, the equipment was coming together and our first soundscape recordings were underway.
With the construction phase coming to an end, there was only one major question left: where exactly will we put everything?
When the plan changed
Finding a suitable experimental site turned out to be one of the more complicated parts of the project.
Our original plans involved a site in a nearby marina, but the situation changed when we were informed that construction work was planned close to the site. The associated noise would have interfered with the acoustic conditions required for our experiment, making the location unsuitable for our setup. We therefore had to move the experiment to a different location at relatively short notice. This meant adapting the setup and transporting the frames again. In the end, we found our new home at Puerto América, at the north-eastern tip of the city.
The change was a good example of how fieldwork can sometimes require a little flexibility. You can spend weeks discussing the experimental design, the set up and the site selection, but once you actually arrive at the water, there are always things that you could not have predicted from a map.
The new location gave us enough space for the experimental setup and allowed us to continue with the project. Hence, the frames were finally transported to Puerto América, weighted and installed.
Getting the frames into the water was actually much easier than building them in the first place. Once we had transported the frames to the harbour, we were able to get them into position and secure them relatively smoothly. The real challenge had been the preparation on beforehand: assembling the large PVC structures, attaching all the necessary components and making sure that everything was ready for deployment.
After weeks of preparation, the frames were finally in the water. The structures that we had spent so much time building on land were now ready to become the basis of our experiment.
From this point on, the focus shifted from building the experiment to monitoring what was happening around it.
Hydrophones, boats and one very expensive swim
Once the experiment was running, the HydroMoths became an important part of our regular monitoring. These small underwater recorders allowed us to record the acoustic conditions around our experimental frames and to measure the sound levels reaching the area of the experiment. This helped us to keep track of the underwater soundscape throughout the experimental period and to verify in hindcast what acoustic conditions the organisms on the settlement panels were actually exposed to.
Of course, regular monitorings also meant regularly getting the equipment in and out of the water. And this was when one of our more memorable fieldwork incidents happened. One day, Liam was alone at the harbour and had a fairly straightforward task: retrieve a HydroMoth, download the data and put it back into the water. Everything went well until the moment when the HydroMoth decided to make the last part of the procedure considerably easier for itself.
It slipped out of his hands and disappeared into the water.
We tried to retrieve it by diving down, but the visibility was extremely poor. Finding a relatively small piece of equipment underwater turned out to be much harder than expected, and despite our efforts, we could not recover it. It was certainly not part of the original plan, but fortunately, the experiment could continue. The lost HydroMoth has since become one of those fieldwork stories that is much easier to laugh about afterwards.
The regular monitorings also revealed how quickly conditions around the experimental site can change. One day, for example, we arrived at the harbour and found a boat parked remarkably close to our experimental setup, almost directly next to our buoys. Luckily, nothing was damaged and the boat did not cause any problems for the frames, but it was certainly an unexpected sight when we arrived.
Working in a harbour means that we are sharing the space with many other users, and sometimes the surroundings have a few surprises in store for us. Fortunately, most of them have been harmless so far.
From PVC panels to marine communities
The most interesting changes, however, did not happen above the water.
They happened on the settlement panels.
At the beginning of the experiment, the panels were simply pieces of PVC. We sanded their surfaces and standardized them so that they would provide suitable settlement substrates for marine sessile organisms. After deployment, there was not much to see.
Then the first organisms started to arrive.
During the first sampling events, we began to see the panels changing. Small organisms had settled on the surfaces, and the communities became increasingly diverse. Ascidians and bryozoans were among those colonizers that became particularly noticeable, together with worms, crustaceans and algae.
Suddenly, the panels that we had spent weeks preparing were becoming real pieces of habitat.
That was probably one of the most rewarding moments of the project. You knew exactly what a panel looked like before it went into the water. Then you retrieve it a few weeks later and had to figure out what has colonized it.
Some organisms were relatively easy to recognize. Others required a microscope, identification guides and considerably more patience.
Our supervisor was a huge help with this part of the project, especially when it came to identifying organisms that were less obvious at first glance. What initially looked like a small patch of something growing on a panel, could turn out to be an entirely different taxonomic group once you took a closer look.
And sometimes the organisms were simply fascinating to look at.
Despite the fauna and flora on the panels, we encountered small crustaceans, fish and other animals using the experimental structures as a habitat. One particularly photogenic shrimp even ended up on Liam’s hand during sampling.
The panels were therefore becoming more than just experimental units. They were small snapshots of the underwater world and the marine biodiversity around Cádiz.
The scientific question remained whether the different acoustic conditions influence the development of the communities. But before we could answer that, we had to document what was actually there.
And that meant sampling.
Sampling in the field
Our first sampling event made another aspect of fieldwork very clear: sometimes there is no perfect laboratory waiting for you at the harbour.
Since our experimental site was relatively far from the university facilities, we transported the equipment we needed directly to the field site by car. This included the microscope and the other equipment needed to examine, photograph and document the settlement panels.
There was no perfect laboratory waiting for us at the harbour. So, we built one.
We set up a small temporary workspace close to the experimental site and arranged everything we needed for the sampling. With the microscope, cameras, laptops, sampling equipment and the panels themselves, we quickly had our own little field laboratory ready to go.
Once everything was set up, the panels came out of the water. One by one, they were photographed, examined and assessed for the organisms that had settled on their surfaces. Some could be identified relatively easily, while others required a closer look under the microscope and a little more time.
The same basic procedure was repeated during the following sampling event, allowing us to compare how the panels had changed over time and which organisms had newly appeared or become more abundant.
Working directly at the field site also had its advantages. Instead of transporting the panels back and forth, we could examine and document them close to where the experiment was running and get an immediate impression of how the communities were developing.
Of course, the conditions were not always perfectly calm. Strong winds can make working at the harbour considerably more challenging, and this is where we really began to appreciate the Levante, the strong easterly wind that regularly affects the Cádiz area. By “appreciate”, we mean learning very quickly how much more complicated even a routine sampling day can become when the wind picks up. Even simple tasks require more coordination, especially when working with equipment and panels close to the water.
Nevertheless, the sampling days became one of the most interesting parts of the experiment so far. Every time we brought a panel out of the water, there was something new to discover.
The youngest member of the GAME team
There was also one very important member of the team who deserves a special mention.
During one of our most recent monitoring days, we had some unexpected assistance from a four-year-old.
While we were reading out the equipment, working on the frames and dealing with the usual collection of sampling tasks, our youngest helper decided that watching from the side was not enough. He wanted to participate.
So he did.
For a short time, we had officially found the youngest member of the GAME team. He may not have been able to explain the experimental design or tell us anything about sound pressure levels, but he was very enthusiastic about helping with the work. It was a small moment, but it was also a nice reminder that fieldwork is rarely as isolated as it can sound when described in a scientific paper. People around us had become part of the experience, whether they were helping with equipment, giving advice, asking questions or simply were curious about what two researchers are doing at the harbour with a collection of PVC pipes.
And occasionally, they became part of the team.
Life outside the frames
Of course, our time in Cádiz did not consist entirely of PVC, HydroMoths and sampling.
Living in Cádiz for several months also meant getting to know the city and the surrounding region outside the harbour. We spent a lot of our free time near the sea, whether that means going to the beach, playing sport or simply enjoying the city after a long day of fieldwork. With beaches, the old town and the harbour all within easy reach, there was usually no shortage of places to spend a few hours away from the experiment.
We have also used our time here to explore more of Andalusia. We visited Sevilla, where we could experience one of the region’s larger and more historic cities, and travelled to Tarifa, where we joined a whale watching trip and got to see some of the marine wildlife of the area from a completely different perspective.
Other trips took us to places such as Zahara de la Sierra, a small mountain town overlooking the reservoir, and Ronda, famous for its spectacular location above the deep El Tajo gorge.
These trips were a welcome change from our usual routine and gave us the opportunity to see a little more of the region we called home for the duration of the project.
The weather had certainly helped. Temperatures were regularly around 30 degrees, although the strong winds could make the conditions feel very different. After spending a day working at the harbour, a few hours at the beach were therefore not the worst way to finish the day.
Andalusia has also experienced some major environmental events while we had been here. Large wildfires affected parts of the region during the summer, although Cádiz itself was not directly affected.
Then there was the solar eclipse.
Cádiz experienced a partial solar eclipse, which gave us the opportunity to witness something very different from our usual fieldwork. For a short time, the attention of the two marine biologists was directed away from the water and towards the sky.
It was a nice change from looking down at the panels.
Poco a poco
Looking back at the time in Cádiz, the project had not developed exactly as we imagined it would.
We changed the experimental site. We rebuilt parts of the setup. We carried heavy concrete across the city. We improvised a sampling station outside. We dealt with strong winds, boats appearing where they were not supposed to be and one HydroMoth disappearing into the sea.
But at the same time, the experiment was running.
The frames were in the water. The HydroMoths were recording. The speakers were playing their experimental soundscapes. And the settlement panels slowly became colonized by marine organisms.
That is probably the most satisfying thing about seeing the project now compared with the beginning. In April, most of what we had was equipment, plans and a long list of things that still needed to be done. At the end, there was an actual marine community growing on the structures we built.
And all the observations that we made are now data that can be analysed.
Perhaps the best way to describe fieldwork in Cádiz is with a phrase we have heard and used plenty of times:
Poco a poco.
Little by little, the experiment was coming together.
Hasta luego, Cádiz!
Carlos & Liam
