NP-seminar: Early initiation of sea ice algal growth under extremely low light intensities at Station North, Greenland (81.3 °N)

Ved: Brian Keith Sorrell, Aarhus University, Denmark, USA.

Microalgae colonizing the underside of sea ice in spring are a key component of the Arctic food web as they drive early primary production and transport carbon from the atmosphere to the ocean interior. The onset of the ice algae spring bloom is usually limited by light availability, and typically a few tens of centimetres of snow is enough to prevent sufficient solar radiation from penetrating through for algal growth.

We documented the initial phase of ice algae growth under approx. 1 m thick snow on top of >1 m of sea ice, under land-fast first-year ice at Station North in north-east Greenland.

Ice algae growth began in May despite extremely low irradiance (<0.17 mmol photons m–2 s–1), and was documented as an increase in Chlorophyll a (chl a), increase in algal cell number, and viable phototrophic activity (quantum yield) in both the bottom of the sea ice and in the underlying water. Snow thickness changed little during May, however the snow temperature increased steadily, as observed from high frequency temperature profiles.

We propose that changes in snow optical properties, caused by temperature-driven snow metamorphosis, was the primary driver allowing for sufficient light to penetrate through the thick snow and ice to initiate algae growth below the sea ice over the total approx. 2 m thick snow plus ice cover.