Blog entry by Luis Greiffenhagen
While we have been talking a lot about biological highlights, it really is the geology of the Whittard Canyon, that makes it so special. Merely everything in the canyon can be traced back to geology: At first, there are the geological structures, that then enable certain physical processes (oceanography, sedimentology), which eventually favour conditions that make our study site biologically so important and diverse. This shows again, how great it is to have an interdisciplinary research cruise, and secondly, calls for a blogpost about geology.
The Whittard Canyon is a geological highlight. It connects the continental shelf of the Celtic Margin (ca. 100-200m depth) with the deep abyssal plain of the Atlantic Ocean (4000m+). Cutting open the elsewhere submerged seabed, it gives geologists insight into different stratigraphic units and formations, e. g. different times of the earth’s history.
Until now, the geological reconstruction of this area is primarily based on geophysical data (seismics and echosounder) at a resolution which allows for a regional scale assessment – but more detail is needed to understand the history of our continental margin. We still are trying to understand exactly when it was formed and what the specific drivers are. The canyon itself has been created by a variety of erosional processes, such as gravitational flow (underwater avalanches / landslides), downslope currents and glacial forces, from times when the continental shelf was glaciated (covered by ice).
Different units eroded differently, giving the canyon its shape. Today, ongoing erosion leads to sudden cliff collapses in the canyon. This, in turn, exposes hard substrate, creates terraces and overhangs in the canyon – and eventually habitat for the diverse fauna of the Whittard Canyon. The next ROV image shows perfectly how geology and biology are linked. If you want to know more about cliff collapses in Whittard Canyon, have a look at Gareth’s paper.
Cliff collapses are a common dynamic process within the canyon. We were able to see evidence for recent events on our dives. The boulders on the next picture could be from such an event.
Other important research questions remain, such as why continental margins that undergo completely different geological processes can develop very similar morphologies. For example canyons in the Mediterranean Sea like the Squilace Canyon in the Ionian Sea incising a very tectonically active margin, show similar dimensions and morphologies to Whittard Canyon (on a passive margin). For this reason, our geologist Silvia Ceramicola will be leading a subsequent expedition with Veerle, funded by the Eurofleets+ programme to Squilace Canyon in next year.
ROV Isis Dive 392 on Monday was entirely dedicated to geological sampling. Gareth and Silvia designed waypoints at a nickpoint (sudden drop of terrain within the bottom of a marine valley), where conditions would allow the ROV pilots to sample rock by drilling and grab samples. We picked up carbonate rocks that were formed by marine sedimentation, millions of years ago. The samples will be analysed and identified later on shore. It is a very special situation for geologists, using the ROV live video and very detailed bathymetry (2m resolution image of the seafloor) to pick points of interest on the go and being able to drill rock at depth. It is like walking around on a beach, picking up stones and looking at cliffs, except under kilometers of water.
Another geological instrument that we have onboard is a sub bottom profiler. Using low frequency acoustics, a sounds signal is sent from our ship that penetrates the seafloor and, depending on the strength of the echo, gives us an insight what lies beneath.
Thereby, we see sedimentation layers or even find ancient, extinct coral reefs that are submerged under the seabed and can give us a hint on what the ocean looked like, thousands of years ago. When taking a core, organic carbonate can be dated, which may explain us in what palaeoceanographic conditions these ecosystems lived, and how climatic change impacted their distribution, thousands of years ago. This will help us understand the impacts of human-induced climate change today and the future.
Thank you to our geologists Gareth Carter (British Geological Survey) and Silvia Ceramicola (National Institution of Oceanography and Applied Geophysics, Italy) for your support making this blogpost.