Pelagic and Sympagic Biogenic Silica Production During Arctic Spring Diatom Bloom in Baffin Bay: Drivers, Limitation, and Fate

Abstract

Silicon (Si) cycling regulates diatom production and export in the Arctic Ocean, yet quantitative constraints on Si sources, recycling, and losses remain limited, particularly in ice‐covered systems. In this study, we quantify biogenic silica (bSiO ₂ ) production, dissolution, and export during a coastal Arctic spring bloom in Baffin Bay, integrating ice‐associated and under‐ice pelagic processes using in situ measurements collected during two ice camps of the Green Edge project (2015, 2016). These first direct measurements of sympagic bSiO ₂ production ranged from 1.5 to 4.5 mmol Si m ⁻² and accounted for less than 3% of total seasonal bSiO ₂ production. In contrast, under‐ice pelagic production was intense, with an early onset, reaching up to 10–12 mmol Si m ⁻²  d ⁻¹ and totaling 55–177 mmol Si m ⁻² over the productive period. Both ice and pelagic diatoms exhibited silicon limitation despite ambient dissolved silica concentrations of 3–6 μmol L ⁻¹ . Dissolution of bSiO ₂ within the ice sustained a significant part of the production, accounting for up to 19%–35% of diatom Si demand. However, dissolution and measured vertical export fluxes (≤6 mmol Si m ⁻² ) together accounted for only a small fraction of pelagic bSiO ₂ production, implying substantial additional loss pathways such as lateral advection and episodic export events. These results demonstrate a strong decoupling between bSiO ₂ production, recycling, and export during Baffin Bay Arctic spring bloom. Our study provides new quantitative constraints on Arctic Si cycle and emphasizes the need to resolve seasonal and spatial variability in Si fluxes to predict future biogeochemical responses to ongoing Arctic change.