Concentrations and sinking rates of particulate biogenic silica, chlorophyll a and phaeopigments, as well as the abundances of the major phytoplankton species, were studied in the Eastern Laptev Sea and the lower Lena River. The results reflected the successional stage of a late summer phytoplankton community, characterized by dominance of small autotrophs and patchy distribution of senescent diatoms no longer able to affect the relative high levels of dissolved silica supplied by the Lena River.