Differences in Sinking Processes and Biological Pump Contribution Among Phytoplankton Groups in the Mesopelagic Layer

Summary

Abstract The differing contributions of phytoplankton groups to biological pump have been insufficiently explored. We evaluated the sinking of phytoplankton in the mesopelagic layer using 16S rRNA gene amplicon sequencing. Sinking particles were collected from June to August 2022 in the Sea of Japan using sediment traps moored at depths of 387 and 890 m. Morphologically categorized fecal pellets—ellipsoidal, cylindrical, spherical, and tabular types—were analyzed for their carbon content and phytoplankton assemblages as well as the bulk and non‐fecal particles. Fecal pellets contributed ≤4.1% and ≤8.0% of the total particulate organic carbon (POC) flux at 387 and 890 m depths, respectively. Ellipsoidal pellets, likely of appendicularian origin, accounted for 59.3%–78.5% of the fecal pellet