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

• Published in: Scientific Reports
• Main Authors: Cimoli, E, Lucieer, V, Meiners, KM, Chennu, A, Castrisios, K, Ryan, KG, Lund-Hansen, LC, Martin, A, Kennedy, F, Lucieer, A
• Format: Article in Journal/Newspaper
• Language: English
• Published: Nature Publishing Group 2020
• Subjects: hyperspectral; sea-ice; Sea ice
• Online Access: https://eprints.utas.edu.au/35716/; https://eprints.utas.edu.au/35716/1/142129%20-%20Mapping%20the%20in%20situ%20microspatial%20distribution%20of%20ice%20algal%20biomass.pdf

Ice-associated microalgae make a significant seasonal contribution to primary production and biogeochemical cycling in polar regions. However, the distribution of algal cells is driven by strong physicochemical gradients which lead to a degree of microspatial variability in the microbial biomass that is significant, but difficult to quantify. We address this methodological gap by employing a field-deployable hyperspectral scanning and photogrammetric approach to study sea-ice cores. The optical set-up facilitated unsupervised mapping of the vertical and horizontal distribution of phototrophic biomass in sea-ice cores at mm-scale resolution (using chlorophyll a [Chl a] as proxy), and enabled the development of novel spectral indices to be tested against extracted Chl a (R2 ≤ 0.84). The modelled bio-optical relationships were applied to hyperspectral imagery captured both in situ (using an under-ice sliding platform) and ex situ (on the extracted cores) to quantitatively map Chl a in mg m−2 at high-resolution (≤ 2.4 mm). The optical quantification of Chl a on a per-pixel basis represents a step-change in characterising microspatial variation in the distribution of ice-associated algae. This study highlights the need to increase the resolution at which we monitor under-ice biophysical systems, and the emerging capability of hyperspectral imaging technologies to deliver on this research goal.