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MEPS prepress abstract   -  DOI:

Effects of increased irradiance on biomass, photobiology, nutritional quality, and pigment composition of Arctic sea ice algae

Lars Chresten Lund-Hansen*, Ian Hawes, Kasper Hancke, Nicole Salmansen, Johanne Raakjær Nielsen, Laura Balslev, Brian K. Sorrell

*Corresponding author:

ABSTRACT: Ice algae are key contributors to primary production and carbon fixation in the Arctic and light availability is assumed to limit their growth and productivity. This study investigated photo-physiological responses in sea ice algae to increased irradiance during a spring bloom in West Greenland. During a 14-day field experiment, light transmittance through sea ice was manipulated to provide three under-ice irradiance regimes i.e. low (0.04), medium (0.08), and high (0.16) transmittances. Chlorophyll a decreased with elevated light availability relative to the control. Maximum dark-adapted photosynthetic efficiency (ΦPSII_max) showed an initially healthy and productive ice algae community (ΦPSII_max > 0.6) with ΦPSII_max decreasing markedly under high light treatments. This was accompanied by a decrease in the light utilization coefficient (α) and photosynthetic capacity (rETRmax), and a decrease in the ratio of MUFA:PUFA fatty acids. This was partly explained by a corresponding increase of photoprotective pigments (diadinoxanthin and diatoxanthin), and a development of mycosporine-like amino acids (MAAs) as identified from a distinctive spectral absorption peak at 360 nm. After 14 days, in situ fluorescence imaging revealed significant differences in ΦPSII_max between treatments of dark-adapted cells (i.e., those sampled before sunrise and after sunset), during diel cycles, with clear chronic photoinhibition in high and medium treatments. Data demonstrate the high sensitivity of spring blooming Arctic sea ice algae to elevated irradiance caused by loss of snow cover. The predicted loss of snow cover on landfast ice will impact negatively on ice algae, their potential primary production and nutritional quality for higher trophic levels.