There is a growing interest to understand how different reactive silicon pools contribute to the marine silicon budget. Quantifying reactive (and potentially bioavailable) silica associated with the different pools – weak acid-leachable Si (Si-HCl), alkaline-leachable Si (Si-Alk) and strong alkaline-leachable Si (Si-NaOH) – is integral for our understanding of early sediment diagenesis. Furthermore, the stable silicon isotopic composition (δ³⁰Si) of these pools can shed light on their formation processes. However, previous studies using sequential leaching techniques lack δ³⁰Si data, thus overlooking potential mechanisms and processes driving silica formation. To date, only a handful of studies have conducted sequential leaching experiments, showing the potential for a link between silica diagenesis and iron cycling within marine sediments. However, these studies are mostly limited to the northern hemisphere and predominantly focused on temperate coastal environments.

Given that iron is a limiting nutrient and silicon is essential for diatom production, which drives primary productivity in the Southern Ocean, unravelling the factors controlling iron and silicon production in sediments and the exchange between sediments and seawater in fjords is essential. Here we present the first results from sequential leaching of sediments from three fjords along the West Antarctic Peninsula. Additionally, we conducted parallel leach experiments for iron and measured the concentration of both Si and Fe in these leaches to assess the association of iron with reactive Si pools and vice versa. Our findings reveal the spatial variability in these pools across the studied fjords, highlighting nuanced differences crucial for understanding sediment diagenesis in polar environments.