Snow Algae Preferentially Grow on Fe-containing Minerals and Contribute to the Formation of Fe Phases

Snow algae growth and mineral dust deposition are both known to strongly decrease snow albedo. Previous work has shown snow algae growth is enhanced in the presence of trace nutrient-containing minerals. Increased dust deposition with aridification due to climate change may therefore additionally enhance snow algae growth. Here we performed batch growth experiments with a snow alga (Chloromonas brevispina) and bacteria co-culture and the minerals andradite (Ca_3.0(Fe_0.6,Al_0.43)₂(SiO₄)₃), olivine (Mg_1.8Fe_0.2SiO₄), and quartz (SiO₂), to observe differences in snow algae attachment to mineral surfaces with differing iron (Fe) contents. In the presence of olivine, which has a low Fe content (∼9%), the number of snow algae on the surface of the olivine decreased with decreasing concentrations of snow algae in the medium. In contrast, in the presence of andradite, which has a higher Fe content (∼16%), the number of snow algae on the surface of andradite remained high even when concentrations of snow algae in the medium were greatly decreased. Additionally, µX-ray Fluorescence (µXRF) measurements indicate greater formation of Fe-containing precipitates on the mineral surfaces in the presence of the snow algae cells than in abiotic controls. These results show that the snow alga both preferentially grows on Fe-rich surfaces and forms Fe-containing precipitates, indicating the presence of a potential positive feedback system that could amplify the effect of dust deposition on snow albedo and therefore climate change.