The production of biogenic silica and its accumulation on the southeastern Bering Sea shelf

Abstract

Silicic acid uptake rates, biogenic silica concentrations, and 210Pb sedimentation rates were measured on the southeastern Bering Sea shelf. These rates are used to describe the distribution of biogenic silica and approximate a steady-state budget for silica on the outer shelf of the Bering Sea. Specific uptake velocities ( Vo) in the upper 10 m range from 0.002 to 0.015 h −1. No significant differences in specific uptake velocities were found between the coastal, middle, and outer domains. Average concentrations of biogenic silica were 299 and 429 mmol m −2 in the middle and coastal domains, respectively. The lower concentration in the outer shelf, 91 mmol m −2, was a result of greater grazing stress on diatom phytoplankton in that area. The estimated annual production of biogenic silica is 2.87 mol Si m −2 y −1 on the middle shelf and 1.64 mol Si m −2 y −1 on the outer shelf. The 210Pb-derived sedimentation rate in the outer domain is 700 to 877 g m −2 y −1; 7 to 10% of the sediment is amorphous silica. Diffusive fluxes of silicic acid from the bottom, based on the gradients in interstitial silicic acid, are 114 to 276 mmol m −2 y −1 or 7 to 17% of outer shelf silica production. Assuming no advection of biogenic silica onto or from the outer domain, up to 65% of the biogenic production is incorporated into surface sediments and an estimated 18 to 35% dissolves in the water column.