Using under-ice hyperspectral transmittance to determine land-fast sea-ice algal biomass in Saroma-ko Lagoon, Hokkaido, Japan

• Published in: Annals of Glaciology
• Main Authors: Pat Wongpan, Daiki Nomura, Takenobu Toyota, Tomonori Tanikawa, Klaus M. Meiners, Tomomi Ishino, Tetsuya P. Tamura, Manami Tozawa, Yuichi Nosaka, Toru Hirawake, Atsushi Ooki, Shigeru Aoki
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press 2020
• Subjects: Biogeochemistry; sea ice; sea-ice ecology; Meteorology. Climatology; QC851-999; Arctic; Annals of Glaciology; Antarc*; Antarctica; ice algae; ice core; Sea ice
• Online Access: https://doi.org/10.1017/aog.2020.69; https://doaj.org/article/c67dee2f80d14a11b824ef11c5c75e3f

Sea ice, which forms in polar and nonpolar areas, transmits light to ice-associated (sympagic) algal communities. To noninvasively study the distribution of sea-ice algae, empirical relations to estimate its biomass from under-ice hyperspectral irradiance have been developed in the Arctic and Antarctica but lack for nonpolar regions. This study examines relationships between normalised difference indices (NDI) calculated from hyperspectral transmittance and sympagic algal biomass in the nonpolar Saroma-ko Lagoon. We analysed physico-biogeochemical properties of snow and land-fast sea ice supporting 27 paired bio-optical measurements along three transects covering an area of over 250 m × 250 m in February 2019. Snow depth (0.08 ± 0.01 m) and ice-bottom brine volume fraction (0.21 ± 0.02) showed low (0.06) and high (0.58) correlations with sea-ice core bottom section chlorophyll a (Chl. a), respectively. Spatial analyses unveiled the patch size of sea-ice Chl. a to be ~65 m, which is in the same range reported from previous studies. A selected NDI (669, 596 nm) explained 63% of algal biomass variability. This reflects the bio-optical properties and environmental conditions of the lagoon that favour the wavelength pair in the orange/red part of the spectrum and suggests the necessity of a specific bio-optical relationship for Saroma-ko Lagoon.