Snow algal blooms in Antarctic King George Island in 2017–2022 and their future trend based on CMIP6 projection

Snow algal blooms have a remarkable climatic or environmental effect through influencing the snow–albedo feedback, accelerating the melting of surface snow, and amplifying global warming. Snow algal blooms occurred frequently on King George Island, Antarctic, during the recent six austral summers (December to next February) through 2017–2022. Based on an assessment of satellite images, this study found that the range and amount of snow algal blooms in the summers of 2018, 2020, 2021 and 2022 are relatively larger than in the summers of 2017 and 2019. Whether meteorological conditions have shaped the year-to-year variation of algal bloom intensities is analyzed through observational composite. The results suggest that during the strong bloom summers there exist prevailing northerly or northwesterly wind anomalies which advect warm and humid airmass from the southern ocean into the island, increasing surface air temperature and humidity; the warmer and more humid surface favors melting of snow and an increase of low cloud cover, subsequently enhancing the atmospheric downward long-wave radiation and amplifying surface warmth; the increased low cloud cover reflects more ultraviolet rays back to space and weakens the short-wave radiation reaching the surface. All these factors together favor to a stronger bloom. In comparison, during 2017 and 2019 there exist weak southerly wind anomalies which induce the northward advection of cold and dry air from the Antarctic Continent and favor the cooler surface. Consequently, it is unfavorable for the snow algal bloom. Based on these results, a snow algal bloom potential index (API) integrating the meteorological conditions is constructed, and its future trend is projected based on the EC-Earth3 run attending the CMIP6 under SSP245 and SSP585. A significant increasing trend is projected especially under SSP585. Thus snow algal bloom on King George Island will become more frequent and stronger in future. This implies a potential accelerate melting of ice shelf over Antarctic Peninsula.