Metabarcoding of microeukaryotes in surface sediments from the Pacific Arctic and adjacent sea areas: The role of diatoms in the biological pump

Abstract

To better understand the importance of diatoms in carbon burial and biological pumps in the Pacific Arctic, we analyzed the microeukaryotic assemblages in twenty-six surface sediments from the northern Bering and Chukchi Seas and adjacent sea areas by metabarcoding the V4 region of the 18S rRNA gene. Biogenic elements were measured, and the contributions of diatoms to sediment carbon are discussed. A total of 618 operational taxonomic units (OTUs) of microeukaryotes were identified. Microalgae accounted for a majority of the DNA reads. Diatoms predominated in the microeukaryotic sequences, and Chaetoceros socialis was the most dominant species, especially in the Bering and Chukchi Seas. The microeukaryotic community was different in the northern deep sea, as represented by the decrease in algal and diatom reads. Organic carbon mainly originated from marine sources in the Chukchi Sea, while the Bering Sea and northern deep seas had relatively more terrestrial inputs based on the TOC/TN data. High BSi concentrations (average > 5% with a maximum of 12.87%) and BSi/TOC ratios (average > 2%) in the Bering and Chukchi Seas indicated the high diatom productivity and efficiency of the silicate pump. Diatom DNA reads were positively correlated with all biogenic elements, indicating that diatoms play an important role in organic matter burial, especially for the dominant diatom species C. socialis due to its fast growth rate and bloom- and spore-forming abilities.