Photophysiology and albedo-changing potential of the ice algal community on the surface of the Greenland ice sheet

Abstract

Darkening of parts of the Greenland ice sheet surface during the summer months leads to reduced albedo and increased melting. Here we show that heavily pigmented, actively photosynthesising microalgae and cyanobacteria are present on the bare ice. We demonstrate the widespread abundance of green algae in the Zygnematophyceae on the ice sheet surface in Southwest Greenland. Photophysiological measurements (variable chlorophyll fluorescence) indicate that the ice algae likely use screening mechanisms to downregulate photosynthesis when exposed to high intensities of visible and ultraviolet radiation, rather than non-photochemical quenching or cell movement. Using imaging microspectrophotometry, we demonstrate that intact cells and filaments absorb light with characteristic spectral profiles across ultraviolet and visible wavelengths, whereas inorganic dust particles typical for these areas display little absorption. Our results indicate that the phototrophic community growing directly on the bare ice, through their photophysiology, most likely have an important role in changing albedo, and subsequently may impact melt rates on the ice sheet.

The role of microbes in snowmelt and radiative forcing on an Alaskan icefield

“…Experimental results presented here, together with previous correlative observations [8][9][10][11][12][13][14][15][16] , laboratory experiments 17 , and theoretical calculations 18 , provide a compelling case for the magnitude of the glacier microbiome's effect on hydrology and climate. Snow algae amplify their albedo reduction through life history, population growth, dispersal, and physiology.…”

“…Fresh snow reflects >90% of visible radiation, but during melt its grain size and water content increase, reducing albedo and further increasing snowmelt 1 . Impurities, including black carbon 3 , dust 4 , and resident microbes [7][8][9][10][11][12][13][14][15][16][17][18][19] , also lower albedo; however, microbes differ from non-living particulates in several critical ways. Perennial populations of photosynthetic microbes actively resurface following overwinter burial by snow 20 , and depend on liquid water and nutrients for survival and reproduction 13,14,[20][21][22] .…”

Biocryomorphology: Integrating Microbial Processes with Ice Surface Hydrology, Topography, and Roughness

“…Slope angle and altitude might influence these blooms since the snowpack [which may inoculate ice surfaces (Hell et al, 2013) and represents a barrier to photosynthesis] likely melts faster on southfacing aspects than shady north-facing ones in the northern hemisphere and vice-versa. Blooms are thought to impact surface albedo and therefore have biocryomorphic significance, although biological darkening is yet to be quantified (Stibal al., 2012a;Yallop et al, 2012). Constraining relationships between topography and biogeochemistry in cryoconite holes and algal blooms may prove fundamental for predicting microbially-mediated melt and biogeochemical cycling at the synoptic-scale.…”

Quantifying bioalbedo: a new physically based model and discussion of empirical methods for characterising biological influence on ice and snow albedo

“…Glacier albedo can also be modified by ice algae, which are taxonomically distinct from the algae that inhabit snow (Uetake et al, 2010;Yallop et al, 2012). Ice algae are dominated by several species of green algae and cyanobacteria.…”

“…Ice algae are dominated by several species of green algae and cyanobacteria. The relative abundance of different species of ice algae and cyanobacteria vary spatially: the green alga Mesotaenium berggrenii has been shown to dominate near the termini of Qaanaaq Glacier (north-western Greenland: Uetake et al, 2010) and Tyndall Glacier (Patagonia: Takeuchi and Kohshima, 2004) and is also present in western Greenland (Yallop et al, 2012). Ancylonema nordenskioldii was found to dominate the upper ablation areas of Gulkana Glacier (Alaska: Takeuchi et al, 2009) and Qaanaaq Glacier (Uetake et al, 2010) and is spread extensively over the western Greenland Ice Sheet along with Cylindrocystis spp.…”