Community-driven variations in snow algae color modulate snow albedo reduction

Snow algae blooms visibly alter snow color and surface energy balance, yet the biological basis of this variability remains unclear. We investigated how pigment composition and community structure shape the optical properties of snow algae blooms of distinct colors – red, orange, and green – co-occurring within the same snowfield in Glacier National Park, USA. We measured the spectral reflectance, pigment composition (HPLC), and algal community composition (18S rRNA amplicon sequencing) of each bloom type to quantify how biological characteristics influence snow reflectance and radiative forcing. Astaxanthin dominated all blooms, while Chla was most abundant in green blooms. Distinct algal taxa characterized each color, with Sanguina dominating red blooms and Chloromonas being more abundant in green and orange. Red blooms showed the lowest reflectance and highest radiative forcing (56 W m⁻²), exceeding that of green (21 W m⁻²) and orange blooms (25 W m⁻²), enhancing energy absorption into the snowpack and promoting localized melting of adjacent ice crystals. Our data indicate that bloom color reflects distinct community compositions, characterized by differences in dominant taxa and pigment pools, which together drive the radiative balance of snowfields. However, these relationships may not be universal, and color is best viewed as an emergent property shaped by multiple biological and environmental factors.