Meltwater as a Local Source of Ice Nucleating Particles in the Central Arctic Summer

Identifying sources of ice nucleating particles (INPs) in the central Arctic is important for understanding controls on the phase of Arctic mixed-phase clouds (AMPCs). We show meltwater samples collected from the Arctic pack ice in July 2020 contain biological INPs active at relatively warm temperatures (T ≥ − 10°C). We attribute the meltwater INPs to organisms and processes unique to a meltwater habitat. Concentrations of biological INPs active at T ≥ − 10°C on filters deployed downwind of meltwater sites showed an enhancement associated with surface proximity. We hypothesize that time over the melt-pond-covered pack ice may have influenced the higher concentrations of biological INPs on the aerosol filters. More work to resolve emission mechanisms from melt ponds is necessary for understanding the extent of this potential source, which may increase importance as melt seasons extend spatiotemporally. Plain Language Summary Understanding what controls cloud properties in the Arctic is important for predicting weather and climate in the region. In this study, we found that, compared to seawater, meltwater on top of sea ice contains high concentrations of ice nucleating particles (INPs), which help form ice in clouds. The meltwater INPs were biological and could trigger ice formation at relatively warm temperatures (above − 10°C). Air samples taken near meltwater areas had more of these particles compared to air from farther away, and the concentration of INPs in the air seemed linked to time spent over the ice rather than over open ocean. This suggests that the melting sea ice surface may be an important source of biological INPs. More research is needed to understand how these particles are emitted from meltwater and how big a role they play in the radiation budget as Arctic melt seasons grow longer and larger.