Microplastics in the sediment of shelves and basins offshore of southern california

, Sarner Rachel, Gray Sarah.

Every year, at least eight million tons of plastic enters the ocean with some sinking to the sea-floor. Micro-sized fibers, granules, plastic films and spherules of plastics (microplastics) are a large part of this pollution. The objective of this research was to develop a methodology to determine how the abundance of microplastics varied with distance from shore/population and with water depth offshore of San Diego. Samples were collected on the RV Sally Ride and RV Sproul research vessels in 2018 using a multicorer, which was deployed at water depths ranging from 100 to 960 meters. In addition, sediments were collected in San Diego Bay for comparison. To extract microplastics from the samples, approximately 100mL of sediment from the upper layer (0-1 cm) of the cores was processed by density floatation in Zinc Chloride (density 1.5 g/cm³). Floating microplastics were transferred onto a gridded filter and systematically categorized and counted under a microscope. Microplastic fibers were found as deep as 960 meters suggesting that plastic pollution is accumulating in the deep basins of the Southern California continental margin. Ongoing analyses of sediments (and analytical blanks) will determine whether microplastic abundance varies with distance offshore or water depth. A better understanding of the microplastic distributions in offshore sediments will help us better predict the impact of plastics on marine life which inhabit the deep sea.

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