Plain language summary
Multi-year landfast sea ice (fast ice) is abundant around the coast of Antarctica. Fast ice is an important component of Antarctic coastal marine ecosystems, providing a prolific habitat for ice algal communities. Although nutrients are essential for biological productivity within sea ice, the status of nutrients and processes affecting nutrient concentrations were previously not known for multi-year fast ice. Here, we collected sea-ice cores from multi-year fast ice in Lützow-Holm Bay, East Antarctica, and we analyzed nutrient concentrations using physical and biogeochemical parameters. Nutrient concentrations in the upper parts of the sea ice decreased due to the accumulation of clean (nutrient-free) snow through melting and refreezing processes, contributing to upward ice growth. In deeper parts of the sea ice, nutrient concentrations were greatly affected by biological processes such as remineralization during the degradation of organic matter within sea ice.