Grain-size effect of biogenic silica in the surface sediments of the East China Sea

Abstract

Biogenic silica (BSi) is an important parameter for understanding biogeochemical processes and paleoceanographic records in the ocean, but this proxy still has many challenges when used to reconstruct changes in the paleoproductivity and evolution of the environment, one of which is the grain size effect. We analyzed the BSi distribution in different size fractions from 8 surface sediments collected in the East China Sea (ECS). We observed the particulate characteristics of diatoms in the water and assessed the grain size effect of BSi. The results suggest the following conclusions: (1) the BSi content of the surface sediments in the ECS is generally below 1%, and the BSi content of different size fractions varies significantly, with largest fraction <16μm, which is approximately 1.1–1.8 times that in the bulk sediments. (2) The variation in the BSi content in different size fractions is largely controlled by the species of diatoms and their cell sizes. In the East China Sea, nano-diatoms are the dominant species, with dominant cells of 2–14μm, resulting in a high BSi content in the fraction <16μm. (3) The hydro-dynamic condition affects the diatom cell size distribution and sediment character, and, thus, has a significant influence on the BSi content of different size fractions. Our research suggests that the grain size distribution of the bulk sediment should be considered when using BSi as a proxy for diatom primary production.