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

• Published in: Scientific Reports
• Main Authors: Cimoli, Emiliano, Lucieer, Vanessa, Meiners, Klaus M., Chennu, Arjun, Castrisios, Katerina, Ryan, Ken G., Lund-Hansen, Lars Chresten, Martin, Andrew, Kennedy, Fraser, Lucieer, Arko
• Format: Text
• Language: English
• Published: Nature Publishing Group UK 2020
• Subjects: Article; Sea ice
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7736878/; http://www.ncbi.nlm.nih.gov/pubmed/33318636; https://doi.org/10.1038/s41598-020-79084-6

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 (R(2) ≤ 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.