Dark microplastics trigger changes on snow metamorphism that depends on the snow initial density

Cryospheric regions are no exception to microplastic ubiquity. Still, microplastic's capacity to decrease snow albedo or advance snow melting, as light-absorbing impurities, remains unexplored. This study assesses the effect of dark microplastics on snow properties under realistic conditions. Six in situ experiments were conducted at the Central Pyrenees (Spain), exposing surface snow to different concentrations of dark micropellets for 4 h. Results were variable and dependent on snow initial conditions. In the experiments performed on recent, light snow (<250 kg m^-3), increasing concentrations of microplastics yielded moderate decreases in albedo and high changes in snow specific surface area, reducing it by 11.4 m² kg^-1 as compared to blank samples, while snowmelt changes were <1%. On the contrary, in the experiments conducted on aged snow of high density (>450 kg m^-3), high microplastic accumulation increased snowmelt 17% more than in the blanks. Further field studies are needed for a better understanding of the effect of microplastics on the global cryosphere.