Abstract
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 milligram 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 midlatitude 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.
Highlights
Snow algae blooms are common in coastal snowpacks of the northern Antarctic Peninsula (AP) and adjacent islands during austral summer
Quality assurance was conducted for each spectrum, and one station (Fildes 5, mixed algae) was removed from the data analysis because the spectral magnitude of R was considered unrealistically high with the highest infrared albedo measured in the study that was not consistent with the spectral shape and pigment content compared to the expected values at the other stations
Albedo integrated across visible wavelengths (400–700 nm) ranged from 0.31 at a green snow algae site on Nelson Island to 0.87 from a clean snow site at Collins Bay on King George Island (Table 1, Fig. 4e)
Summary
Snow algae blooms are common in coastal snowpacks of the northern Antarctic Peninsula (AP) and adjacent islands during austral summer. Unlike other LAPs (Flanner et al, 2007), the “bioalbedo” feedback (Cook et al, 2017) from microbes living and growing on the surface of the cryosphere is not currently accounted for in global climate models, and only one study has assessed the role of red snow algae in RF, in Alaska (Ganey et al, 2017) Living organisms such as snow algae reduce surface albedo differently than LAPs, due to their life cycle response to light (Bidigare et al, 1993; Rivas et al, 2016), the functional role of their pigments in melting snow and ice (Dial et al, 2018), and their strong absorption features as opposed to LAPs’ broad absorption across the visible wavelengths. We evaluate several approaches to estimate pigment concentration that can be applicable to a variety of high-spatial-resolution satellites, including Sentinel-2
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