title: Photobiology of sea ice algae during initial spring growth in Kangerlussuaq, West Greenland: insights from imaging variable chlorophyll fluorescence of ice cores.
abstract: We undertook a series of measurements of photophysiological parameters of sea ice algae over 12 days of early spring growth in a West Greenland Fjord, by variable chlorophyll fluorescence imaging. Imaging of the ice-water interface showed the development of ice algae in 0.3-0.4 mm wide brine channels between laminar ice crystals in the lower 4-6 mm of the ice, with a several-fold spatial variation in inferred biomass on cm scales. The maximum quantum yield of photosynthesis, F(v) /F(m), was initially low (~0.1), though this increased rapidly to ~0.5 by day 6. Day 6 also saw the onset of biomass increase, the cessation of ice growth and the time at which brine had reached <50 psu and >-2 °C. We interpret this as indicating that the establishment of stable brine channels at close to ambient salinity was required to trigger photosynthetically active populations. Maximum relative electron transport rate (rETR(max)), saturation irradiance (E(k)) and photosynthetic efficiency (α) had also stabilised by day 6 at 5-6 relative units, ~30 μmol photons m⁻² s⁻¹ and 0.4-0.5 μmol photons m⁻²s⁻¹, respectively. E(k) was consistent with under-ice irradiance, which peaked at a similar value, confirming that daytime irradiance was adequate to facilitate photosynthetic activity throughout the study period. Photosynthetic parameters showed no substantial differences with depth within the ice, nor variation between cores or brine channels suggesting that during this early phase of ice algal growth cells were unaffected by gradients of environmental conditions within the ice. Variable chlorophyll fluorescence imaging offers a tool to determine how this situation may change over time and as brine channels and algal populations evolve.
authors.affiliation: Gateway Antarctica, Private Bag 4800, Christchurch, New Zealand.
authors.forename: Ian
authors.initials: I
authors.lastname: Hawes
authors.forename: Lars Chresten
authors.initials: LC
authors.lastname: Lund-Hansen
authors.forename: Brian K
authors.initials: BK
authors.lastname: Sorrell
authors.forename: Morten Holtegaard
authors.initials: MH
authors.lastname: Nielsen
authors.forename: Réka
authors.initials: R
authors.lastname: Borzák
authors.forename: Inge
authors.initials: I
authors.lastname: Buss
mesh_terms: D018533:Biomass; D002734:Chlorophyll / Q000378:metabolism*; D006116:Greenland; D007053:Ice; D058086:Microalgae / Q000378:metabolism*; D008854:Microscopy, Electron; D018462:Photobiology; D012623:Seawater
chemical_list: D007053:Ice; D002734:Chlorophyll