Mapping the *in situ* microspatial distribution of ice algal biomass through hyperspectral imaging of sea-ice cores

Ice-associated microalgae significantly contribute to primary production in polar regions, but strong physicochemical gradients create microspatial variability in biomass that is difficult to quantify. This study presents a field-deployable hyperspectral scanning and photogrammetric approach to map vertical and horizontal distributions of phototrophic biomass in sea-ice cores at millimeter-scale resolution, using chlorophyll a (Chl a) as a proxy. Novel spectral indices developed from core transmittance measurements were tested against extracted Chl a (R² ≤ 0.84). The resulting bio-optical relationships were applied to hyperspectral imagery captured both in situ (under-ice sliding platform) and ex situ (extracted cores) to quantitatively map Chl a (mg m−2) at high resolution (≤2.4 mm). This per-pixel optical quantification provides a step-change in characterizing microspatial variability of ice-associated algae and highlights the need for higher-resolution monitoring of under-ice biophysical systems, demonstrating the capability of hyperspectral imaging technologies to achieve this.