News
Luke Publishes in QSR!
Luke has been diligently keeping his head down over the last few months. He recently got his paper published in the academic journal Quaternary Science Reviews!
The paper investigates how ice-rafted debris (IRD) is deposited on the Porcupine Bank Canyon. Today, we know corals love living there (i.e. Appah et al., 2020). When we look at the seafloor data though, we found weird looking erratic patterns in the seabed, called ploughmarks . These occur when glaciers become grounded and scour through the top few meters of the seafloor. Which got us thinking – if these were indeed caused by grounded glaciers, what impact this have had on the benthos?
To answer this question, we want to look through geological time, will allow us to interpret what perhaps caused these ploughmarks. As such, we used an ROV-vibrocorer to acquire a numerous samples from the western Porcupine Bank and Porcupine Bank Canyon.
With these cores, we then used a CT-scanner to acquire density images of the internal components of the cores. These images were then processed using 3D segmentation software, to classify what is hard and what is not. The software also calculates size and quantities every 0.02 cm. One of the cores, which is the focus of the paper, is characteristically rich in IRD. Other comparative IRD records use traditional methods to access IRD quantities. This would entail picking through samples and counting individual grains. Not only is this method laborious (roughly 2 hours of picking per samples), but it is also carried out, typically, ever 2.5 cm of a core. This translates to 80 hours’ worth of sitting behind a microscope for ever one meter of a core. Our methods take, from scanning the cores to processing the data, roughly 5 hours per meter long core. I’m sure with enough practise and if you had a workflow going, I estimate you could probably half this time again.
We then dated the core (no – not taking it out for a milkshake) and measured grain size. When then compared what we found to other IRD records. Here’s what we found:
- IRD was deposited in a series of fluxes to the site. These fluxes agree with other fluxes from the Porcupine Seabight
- Current speeds slow down during cold phases. If you are a stationary coral, this is bad news, as you rely on currents to bring you food and save you from being buried in sediment.
- A gap in our geological record (between 27.3 and 17.2 thousand years ago) may have been caused by iceberg scouring. Sedimentation appears to resume when sea levels rise – meaning that grounded glaciers are lifted from the site. Again, what would this have done to our coral friends? This question is part of my greater thesis of work.
You can find the paper here, give it a go.
References
Appah, J.K.M., Lim, A., Harris, K., Ramsay, R., O’Reilly, L. & Wheeler, A.J. (2020). Are non-coral reef habitats as important to benthic diversity and composition as coral reef habitats in submarine canyons? A rich analysis of organismal distribution controls in the upper Porcupine Bank Canyon, NE Atlantic. Frontiers in Marine Science. https://doi.org/10.3389/fmars.2020.571820.