Extreme Low Light Requirement for Algae Growth Underneath Sea Ice: A Case Study From Station Nord, NE Greenland

Abstract

Microalgae colonizing the underside of sea ice in spring are a key component of the Arctic foodweb as they drive early primary production and transport of carbon from the atmosphere to the ocean interior. Onset of the spring bloom of ice algae is typically limited by the availability of light, and the current consensus is that a few tens‐of‐centimeters of snow is enough to prevent sufficient solar radiation to reach underneath the sea ice. We challenge this consensus, and investigated the onset and the light requirement of an ice algae spring bloom, and the importance of snow optical properties for light penetration. Colonization by ice algae began in May under >1 m of first‐year sea ice with ∼1 m thick snow cover on top, in NE Greenland. The initial growth of ice algae began at extremely low irradiance (<0.17 μmol photons m−2 s−1) and was documented as an increase in Chlorophyll a concentration, an increase in algal cell number, and a viable photosynthetic activity. Snow thickness changed little during May (from 110 to 91 cm), however the snow temperature increased steadily, as observed from automated high‐frequency temperature profiles. We propose that changes in snow optical properties, caused by temperature‐driven snow metamorphosis, was the primary driver for allowing sufficient light to penetrate through the thick snow and initiate algae growth below the sea ice. This was supported by radiative‐transfer modeling of light attenuation. Implications are an earlier productivity by ice algae in Arctic sea ice than recognized previously.

Under‐ice metabolism in a shallow lake in a cold and arid climate

“…Our observations are in accordance with Obertegger, Obrador, and Flaim () who analysed under‐ice DO dynamics in an oligotrophic lake, and with Hanke et al. () who studied phytoplankton growth and photosynthesis under thick snow and sea‐ice in Greenland.…”

Effects of microbial processes and CaCO3 dynamics on inorganic carbon cycling in snow-covered Arctic winter sea ice

“…Nevertheless, the ice algae in this study were able to grow at extremely low irradiance (0.2 µmol photons m −2 s −1 ). This result is comparable to a recent study in Northern Greenland, where ice algae were observed to begin to grow at a light intensity below 0.17 µmol photons m −2 s −1 (Hancke et al 2018).…”

“…These very low algal biomass and productivity values for Young Sound can be attributed to light limitation, given the late-winter sampling date and the heavy snow cover of 70 cm at the FYI site compared to 17 cm at POLY I, as well as other features of the snow and ice. Light attenuation by snow in this study is higher than reported elsewhere (Hancke et al 2018), particularly at the POLY I site (Fig. 1c).…”

Environmental factors influencing the seasonal dynamics of spring algal blooms in and beneath sea ice in western Baffin Bay

“…Low-light conditions are recognized to sustain ice algal growth (Leu et al, 2015;Lacour et al, 2017;Hancke et al, 2018). Although contributions of ice algae to the annual primary production remain highly variable, depending on the season and the region (<1 to 60%; e.g., Loose et al, 2011;Dupont, 2012;Fernández-Méndez et al, 2015), they are a critical food source for the marine food web especially during the winter (Søreide et al, 2010).…”