Modeling seasonal growth of phototrophs on bare ice on the Qaanaaq Ice Cap, northwestern Greenland

Abstract

Glacier phototroph blooms on the surfaces of ice sheets and glaciers cause albedo reduction, leading to increased melting rates. We observed seasonal changes in the abundance of phototrophs on the Qaanaaq Ice Cap in northwestern Greenland from June to August 2014, and reproduced these changes using numerical and empirical models. The phototroph community on the ice surface mainly consisted of the glacier alga Ancylonema nordenskioldii and the cyanobacterium Phormidesmis priestleyi. The glacier alga appeared on the ice surface in late June, after which its abundance increased exponentially throughout the melting period. A logistic growth model designed for snow algal growth reproduced the measured exponential increases, suggesting that growth could be explained using the model as a function of the ice melting duration. Cyanobacteria appeared and their abundance increased in late July but did not change exponentially thereafter. The abundance of cyanobacteria was explained with an empirical model expressed as a function of the amount of mineral dust on the bare ice surface. Our numerical and empirical models for reproducing glacier algae and cyanobacteria could be useful for quantifying the albedo reduction caused by their growth and the melt rates of the Greenland ice sheet and glaciers in the future.

Dark ice in a warming world: advances and challenges in the study of Greenland Ice Sheet's biological darkening

“…As CO 2 is constantly supplied from the atmosphere to the ice surface, where it easily dissolves, it is unlikely to be a limiting factor at the ice surface that the algae inhibit. To date, algal growth has been modelled as a function of the cumulative growth period where environmental conditions allow for algal growth others, 2018, 2020;Onuma and others, 2022). The thresholds of these environmental conditions were defined by Williamson and others (2020) as a snow-free ice surface (snow cover <2 cm), sufficient solar irradiance to drive photochemistry (shortwave radiation >10 W m −2 ) and the availability of liquid water (air temperature >0.5°C).…”

“…The thresholds of these environmental conditions were defined by Williamson and others (2020) as a snow-free ice surface (snow cover <2 cm), sufficient solar irradiance to drive photochemistry (shortwave radiation >10 W m −2 ) and the availability of liquid water (air temperature >0.5°C). In contrast, Onuma and others (2022) used an ice temperature >0°C as a threshold for liquid water availability and did not define a solar irradiance threshold. However, there remains a lack of data to support the environmental conditions and values used as thresholds.…”

“…To define the thresholds for algal light requirements, incubation experiments or field measurements of glacier ice algal activity pre-and during snowline retreat, together with the light transmission through the snow are required. Sampling glacier ice algal populations from beneath the snow or the analysis of regression fits of their biomass progression throughout the season could additionally provide estimates of their initial population size, which is required to model algal bloom progression throughout the season (Williamson and others, 2020;Onuma and others, 2022).…”

The first cultivation of the glacier ice alga Ancylonema alaskanum (Zygnematophyceae, Streptophyta): differences in morphology and photophysiology of field vs laboratory strain cells

“…The cells of some glacier ice algae are five-times more effective energy absorbers than snow algae (Halbach and others, 2022), and such algae are dominant albedo reducers and accelerators of ice thawing. This has been particularly recognized at the south-western margin of the Greenland ice sheet, and over the long term will likely eventually influence the rising rate of the global sea level (Cook and others, 2020; Onuma and others, 2022).…”

“…alaskanum ), isolated from a glacier in the Austrian Alps (Procházková and others, 2021). This is a unicellular species commonly causing blooms in cold regions worldwide, such as Greenland (Uetake and others, 2010; Onuma and others, 2022), southern Chile (Takeuchi and Kohshima, 2004) or the European Alps (Remias and others, 2009). A brief comparison between environmental material and this laboratory strain revealed striking differences in cell lengths, the extent of secondary pigmentation and photophysiological light preferences.…”