Oral Session 3 | Tuesday, October 4, 09:20–09:40 | Abstract 524

Underwater hyperspectral imaging used for measuring light availability and algae biomass under sea ice during the spring bloom in the Arctic

We deployed an Underwater Hyperspectral Imager (UHI) on an instrument-carrying platform consisting of two interconnected mini-ROVs (Remotely Operated Vehicle) to map under sea-ice algae in the Arctic. The aim of the study was to get a more accurate understanding of the light variation under sea-ice and relate it to ice-algae biomass. The study was conducted at about 80° North (south of in Kvitoeya) during the spring bloom in May 2021. In addition to the UHI facing up, the mini-ROVs were carrying an altimeter used to stay at a constant distance of 1m under the ice and a hyperspectral radiometer to measure downwelling light. Simultaneously, a second radiometer was measuring downwelling light above the ice. The survey was conducted under flat ice that had a visible thin layer of ice-algae biofilm. The UHI went back and forth from the ice hole using a USBL for relative positioning. The under-ice light measurements vary in intensity and spectra as a result of varying sea ice and snow thickness. In addition, we used the intensity and spectral signatures to determine the special variation of ice-algae biomass. To our knowledge, this study is the first to look at under ice-algae patchiness on a spatial scale in the Arctic. Ice-algae biomass is traditionally estimated from ice cores resulting in large errors due to the spatial heterogeneity of the algae. This novel approach enables us to better understand both ice light availability and new insights about ice algae patchiness, growth and development during the spring bloom.

*Natalie Summers, NTNU, 0000-0003-0993-0696

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