The Porcupine Abyssal Plain
Blog entry by Luis Greiffenhagen
After spending around two weeks at Whittard Canyon, we travelled further west. After a 24h transit, we reached the Porcupine Abyssal Plain (PAP). It lies in international waters, southwest of Ireland and the Porcupine Seabight. The seafloor is almost four times deeper than most of our dives in Whittard Canyon, with an average depth of 4840 meters. The bottom is mainly flat, consisting of muddy sands, however, there are a few elevations, the so-called “abyssal hills”. Originating from mid-Atlantic tectonic activities millions of years ago, they can be up to 1000m tall.
PAP is uniquely important for deep sea research as a “fixed point observatory”. Together with one other place in the Pacific, it is the only deep-sea site in the world that has been continuously studied for more than 30 years. While scientists like to explore new places, constantly going back to the same place and creating long-term datasets is what helps us understand the processes of a changing ocean. Brian Bett (NOC) who is coordinating the missions at PAP on this cruise was one of the initiators of the PAP programme in the early 1990s, which started as a joint collaboration of German and British scientists. In situ biogeochemical data have been measured ever since, are open access to everyone, and can be explored here alongside other information. PAP is an incredible opportunity to investigate the impacts of climate change on the open ocean and the deep sea. Therefore, our visit to PAP runs under the framework of the CLASS (Climate Linked Atlantic Sector Science) programme.
In our time at PAP, we deployed a CTD (conductivity, temperature, density), took DNA water samples and conducted video surveys with the ROV. This is, excitingly, the first time an ROV has ever gone down to PAP. The dives are long, taking 3 hours just to descend and reach the bottom. This makes sense, considering that it’s the equal height to the Mont Blanc. Down there, we saw amazing creatures, very different to the Whittard Canyon. We had the unique opportunity to sample some species for DNA analyses and other taxonomic reasons. A highlight was a 50cm-long, purple deep-sea cucumber, and a coral that is possibly undescribed. While we were sampling, a group of rattail fishes (Grenadiers) was carefully observing our activities. Further, we still had time to climb one of the abyssal hills with the ROV. When we reached the summit, it felt like a mountaineer, being the first person in the world on this peak.
Last, but not least: as a little funny experiment we all got our personal styrofoam cups – and sent them down to the abyss with the ROV. When our cups came back up, they were much smaller from the immense pressure (more than 400 bar) and oddly deformed. What a souvenir! And even more incredible to think that all the little, fragile looking animals of PAP can withstand that pressure.