ENV-03 Marine Microplastic
Distribution and controlling factors of microplastics in surface sediments of typical deep-sea geomorphological units in the northern South China Sea
Xiaodong Zhang* , State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
Zhifei Liu, State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
Yulong Zhao, State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
Pengfei Ma, State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China
Christophe Colin, GEOPS, CNRS, Université Paris-Saclay, Orsay 91405, France
Andrew Tien-Shun Lin, Department of Earth Sciences, National Central University, Taoyuan 32001, Taiwan

Marine microplastics are widely distributed in deep-sea sedimentary environments and are altering sediment compositions and ecological conditions on the seafloor. However, the relation between the distribution of microplastics in deep-sea sediments and the sedimentary dynamic conditions is poorly understood. In this study, we collected surface sediments from several typical geomorphological units (sand dune, sediment drift, and submarine canyon channel/levee) in the northern South China Sea to study the composition and distribution of deep-sea microplastics and their controlling factors. The results show that the microplastic abundance in surface sediments ranges from 19 to 347 p·kg–1, and the identified microplastics consist of 10 types, including dominant polycarbonate, polyethylene, polyester, polyvinyl chloride, and polypropylene, and minor polyethylene terephthalate, acrylonitrile-butadiene-styrene, epoxy resin, hydrocarbon resin, and acrylic. The abundances and types of these microplastics vary obviously among the different deep-sea geomorphological units. The sand dune and canyon channel contain the highest abundances and more types of microplastics, which are dominated by relatively large-size and high-density polycarbonate or polyvinyl chloride. The canyon levee contains the lowest abundances and less types of microplastics, which are dominated by relatively small-size and low-density polyester fiber or polyethylene. Nevertheless, the microplastic composition of the sediment drift is between those of the canyon channel and the canyon levee. The abundance, type, size, and density of microplastics are all positively correlated with the sedimentary dynamic intensity, which is represented by the mean grain size of detrital sediments. We therefore infer that the sedimentary dynamic conditions control the composition and distribution of microplastics in the deep-sea sediments. This study highlights that some deep-sea environments with stronger sedimentary dynamic conditions may accumulate more microplastics, which is of great significance for evaluating the storage and ecological damage of deep-sea microplastics.

Keywords: microplastics, deep-sea sediments, submarine canyon, sedimentary dynamics, South China Sea