Spectral characterization, radiative forcing and pigment content of coastal Antarctic snow algae: approaches to spectrally discriminate red and green communities and their impact on snowmelt

Abstract

Abstract. Here, we present radiative forcing (RF) estimates by snow\nalgae in the Antarctic Peninsula (AP) region from multi-year measurements of\nsolar radiation and ground-based hyperspectral characterization of red and\ngreen snow algae collected during a brief field expedition in austral summer\xa02018. Our analysis includes pigment content from samples at three bloom\nsites. Algal biomass in the snow and albedo reduction are well-correlated\nacross the visible spectrum. Relative to clean snow, visibly green patches\nreduce snow albedo by ∼40 \u2009% and red patches by\n ∼20 \u2009%.\xa0However, red communities absorb considerably more\nlight per milligram of pigment compared to green communities, particularly in green\nwavelengths. Based on our study results, it should be possible to\ndifferentiate red and green algae using Sentinel-2 bands in blue, green and\nred wavelengths. Instantaneous RF averages were double for green (180\u2009 W\u2009m−2 ) vs. red communities (88\u2009 W\u2009m−2 ), with a maximum of 228\u2009 W\u2009m−2 . Based on multi-year solar radiation measurements at Palmer\nStation, this translated to a mean daily RF of ∼26 W\u2009m−2 \n(green) and ∼13 W\u2009m−2 (red) during peak growing season\n– on par with midlatitude dust attributions capable of advancing snowmelt.\nThis results in ∼2522 \u2009m 3 of snow melted by\ngreen-colored algae and ∼1218 \u2009m 3 of snow melted by\nred-colored algae annually over the summer, suggesting snow algae play a\nsignificant role in snowmelt in the AP regions where they occur. We suggest\nimpacts of RF by snow algae on snowmelt be accounted for in future estimates\nof Antarctic ice-free expansion in the AP region.