master thesis

Concentration and distribution of microplastics in the deep-sea sediments of the Congo Canyon System


Turbidity currents are underwater flows of sediment, and a major process in the distribution of sediment. Submarine canyon systems can stretch for hundreds, if not thousands of kilometres out into the deep ocean. They offer a timeline of sedimentary process, and additionally act as record keeper for our pollution of the rivers and seas. The Congo Canyon is a submarine canyon system off the coast of the Democratic Republic of the Congo, Western Africa with a proximal part in the territorial waters of Angola. Submarine events in the canyon can last weeks and may result in the transport of numerous cubic kilometres of sedimentary material. However, we do not currently know for certain that these events transport plastic, nor how much material they transport. In this project I processed collected cores sediments from the Congo Canyon to remove organic material and isolate microplastics. I analysed them using LD-IR (Laser Direct Infrared Spectroscopy) following the technique developed by the Helmholtz-Zentrum Hereon to determine the presence, frequency, and polymer classification of each sample. Plastics were ubiquitous amongst all of the core samples, and my calculations showed that up to 9,138 microplastic particles per kilogram of sediment were present in the Congo Canyon System. I did not find that grain size impacted the sorting or dispersal of microplastic fragments, however the density of the polymer resulted in preferential deposition, where higher density plastics were deposited earlier in the channel. However, I acknowledge the size of this dataset, and that further interlinking with sediment trap data is required to understand the input of sediment from the water column. I have made recommendations on future lab work, possible refinements to the lab protocol, and additional validation of the current process to further strengthen the applicability of this work.
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