Spatial distribution and abundance of red snow algae on the Harding Icefield, Alaska derived from a satellite image

Abstract

[1] Red snow caused by algal bloom is common on glaciers and snowfields worldwide. Description of spatial distributions of snow algal blooms is important for understanding snow algae's unique life in an extremely cold environment and for determining the effect of algae through the reduction of surface albedo. Here we present the spatial distribution of red snow algae on the Harding Icefield, Alaska retrieved from a satellite image. Field observations on the icefield conducted in August 2001 revealed visible red snow, particularly near the snowline. Field measurements of spectral reflectance on the surface revealed the specific spectral absorption of algal pigments. We found a significant correlation between snow algal biomass and a reflectance ratio of SPOT (Satellite Probatoire d' Observation de la Terre) satellite band of wavelength 610 -680 nm to band 500-590 nm. Using this relationship between the reflectance ratio and algal biomass, we estimated the distribution and abundance of red snow across the icefield using a SPOT satellite image. The spatial distribution of red snow on the icefield obtained by mapping the reflectance ratio matched field observations across the icefield with more red algal blooms on the continental than the maritime side of the icefield. Area averaged mean carbon content estimated from the red algal biomass for the icefield on the image was 1.2 kg km À2 .

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

“…The spectrum at 333 ppm was similar in shape, but with lower values of reflectance, to a theoretical spectral albedo of snow with very high densities of algae 18 . The spectrum at 172 ppm closely matched the field reflectance from a California sample 9 of 2.1 × 10 4 cells ml −1 and less closely a red-snow sample from the Harding Icefield 10 , two studies that observed strong linear relationships between alga abundance and indices based on reflectance features in the 500-700 nm range. We, too, observed a strong linear relationship (NDI-alga model, …”

“…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.…”

“…1). The Harding Icefield has been the site of both previous mass-balance 25 and glacial biota studies 10,41 . We supplemented data from an automated weather station (AWS; RAWS Harding Icefield station http://www.raws.dri.edu/cgi-bin/rawMAIN.pl?akAHAR) 210 m above and <3 km distant from our experimental study site (60.156029 • N 149.794006 • W) with three temperature sensors (Onset, model HOBO Pendant datalogger in radiation shield) maintained 2 m above the snow surface at the vertices of the experimental study site (Supplementary Fig.…”

“…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] .…”

Metagenomic and satellite analyses of red snow in the Russian Arctic

“…In these harsh environments, C. nivalis has 28 adapted to intense UV exposure by producing astaxanthin, a UV-screening pigment that 29 produces a visible red hue in snow (Gorton & 48 band ratios with wavelengths 630 -690 nanometers and 520 -600 nanometers, respectively, 49 were used to detect red snow in the satellite images. The spectral reflectance of red snow shows 50 that it has higher reflectance in the red band than in the green band, while the spectral reflectance 51 of snow and ice has higher reflectance in the green band than the red band (Takeuchi et al 2006). 52 Therefore, red to green reflectance band ratios that are less than 1.0 are more likely to signify 53 white snow or ice while band ratios that are greater than 1.0 are more likely to signify red snow 54 or ice.…”