Spectral Characterization, Radiative Forcing, and Pigment Contentof Coastal Antarctic Snow Algae: Approaches to SpectrallyDiscriminate Red and Green Communities and Their Impact onSnowmelt

Abstract. Here, we present radiative forcing (RF) estimates by snow algae in the Antarctic Peninsula (AP) region from multi-year measurements of solar radiation and ground-based hyperspectral characterization of red and green snow algae collected during a brief field expedition in austral summer 2018. Our analysis includes pigment content from samples at three bloom sites. Algal biomass in the snow and albedo reduction are well-correlated across the visible spectrum. Relative to clean snow, visibly green-patches reduce snow albedo by ~ 40 % and red-patches by ~ 20 %. However, red communities absorb considerably more light per mg of pigment compared to green communities, particularly in green wavelengths. Based on our study results, it should be possible to differentiate red and green algae using Sentinel-2 bands in blue, green and red wavelengths. Instantaneous RF averages were double for green (180 W m−2) vs. red communities (88 W m−2), with a maximum of 228 W m−2. Based on multi-year solar radiation measurements at Palmer Station, this translated to a mean daily RF of ~ 26 W m−2 (green) and ~ 13 W m−2 (red) during peak growing season – on par with mid-latitude dust attributions capable of advancing snowmelt. This results in ~ 2522 m3 of snow melted by green-colored-algae and ~ 1218 m3 of snow melted by red-colored-algae annually over the summer, suggesting snow algae play a significant role in snowmelt in the AP regions where they occur. We suggest impacts of RF by snow algae on snowmelt be accounted for in future estimates of Antarctic ice-free expansion in the AP region.