POSTER Session 1

Application of an Underwater Hyperspectral Imager (UHI) to Identify and Map Distinct Diatom Communities in Arctic Sea Ice

Sea ice algae play a crucial role in polar marine ecosystems, yet their distribution and dynamics are under-studied due to the challenges in accessing and sampling ice-covered environments. Traditional ice coring captures only a small area, failing to represent the true spatial heterogeneity of biomass and bloom phenology. New methods are continuously being developed utilizing the relationship between transmitted irradiance and the bio-optical properties of sea ice algae, enabling broader spatial assessment of algal distribution. In this study, conducted in the Arctic Ocean basins in August 2022, we deployed two Underwater Hyperspectral Imagers (UHI) under the sea ice, one attached to a mechanical arm for fine-scale calibration and the other mounted on to a ROV for broader transects. Moreover, we collected ice core samples for chlorophyll a concentration and in vitro spectral reflectance/absorbance, important for validation of the UHI biomass estimates. We applied a Normalized Difference Index (NDI) to the ROV-UHI surveys to estimate the spatial distribution of biomass across transects covering up to 50 m. Preliminary results revealed two distinct diatom communities dominated by distinct species, only centimeters from each other in a ridge formation, both undetected by ice coring alone. Additionally, we demonstrated the ability to optically differentiate between the two communities in the UHI surveys using target detection algorithms paired with in vitro spectral reflectance/absorbance. Our study demonstrates the capacity of the UHI paired with underwater robots for capturing patchiness in sea ice algal biomass and potential for achieving optical differentiation of different algal communities.

*Janina Osanen, Norwegian University of Science and Technology (NTNU), Norway, https://orcid.org/0009-0001-7856-1137

Benjamin Lange, Norwegian Geotechnical Institute, Norway

Karley Campbell, Arctic University of Norway (UiT), Norway

Geir Johnsen, Norwegian University of Science and Technology (NTNU), Norway

Glaucia Fragoso, Norwegian University of Science and Technology (NTNU), Norway

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