Dissolution Dominates Silica Cycling in a Shelf Sea Autumn Bloom

Abstract

Autumn phytoplankton blooms represent key periods of production in temperate and high-latitude seas. Biogenic silica (bSiO2) production, dissolution, and standing stocks were determined in the Celtic Sea (United Kingdom) during November 2014. Dissolution rates were in excess of bSiO2 production, indicating a net loss of bSiO2. Estimated diatom bSiO2 contributed ≤10% to total bSiO2, with detrital bSiO2 supporting rapid Si cycling. Based on the average biomass-specific dissolution rate (0.2 day−1), 3 weeks would be needed to dissolve 99% of the bSiO2 present. Negative net bSiO2 production was associated with low-light conditions (<4 E·m−2·day−1). Our observations imply that dissolution dominates Si cycling during autumn, with low-light conditions also likely to influence Si cycling during winter and early spring.