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On the composition of suspended particulate matter near the Atacama Trench (Southeast Pacific): A geochemical and electron microscopy study through the euphotic, oxygen minimum, and bathypelagic zones
Summary
Scientists studying the deep waters off the coast of Chile found tiny plastic fibers mixed in with natural ocean particles like algae, minerals, and bacteria, all the way from the sunlit surface down to nearly 3 miles deep. This confirms that microplastics are infiltrating even the most remote ocean environments and settling alongside the marine "snow" that feeds deep-sea ecosystems, raising concerns about how far plastic pollution travels and what it means for marine food chains that eventually connect back to human seafood consumption.
We present new biogeochemical and mineralogical analyses of ocean waters, suspended particulate matter (SPM) and deep seafloor sediments (DSS) across three different sites of the eastern slope of the Atacama Trench in front of northern Chile. These analyses have revealed a singular chemistry of upwelling deep waters from the Humboldt Current with respect to the overlying ocean water. Scanning electron microscopy (SEM) on SPM (including marine snow ) collected at different depths in the water column (20 m to 4500 m) show a high diversity of solids, including biological debris (settling phytoplankton biomass dominated by diatoms), detrital minerals (e.g. quartz, K-feldspar, plagioclase, oxides, clay minerals), authigenic minerals formed in the water column (e.g., calcite, barite), and microplastic fibers. We observed abundant colonization of settling biological particles by rod-shaped bacteria in the sharpest part of the oxycline (at around 50 m depth) and intense heterotrophy (including different groups of sulfate-reducing bacteria) in the oxygen minimum zone (OMZ). The fast degradation of biological matter in the upper layer results in an extremely limited vertical export of organic carbon to the bathyal and abyssal zones. However, the detection of abundant phytoplankton remains (e.g. diatom frustules), lipid biomarkers from the phototrophic active zone (e.g. phytol, fatty acids and sterols) and certain pigments (e.g. carotenoids) in the upper cm of the bottom sediments suggest that a small fraction of organic matter still reaches the deep ocean floor, allowing for microbial activity like sulfate reduction which favors the formation of pyrite below the water/sediment interface.