Assessing the Contributions of Open Ocean, Blowing Snow and Frost Flowers as Sources of Sea Salt Aerosol over Polar Regions

Sea salt aerosols (SSA) are generated via air bubble bursting at the ocean surface, as well as by wind mobilization of saline snow and frost flowers over sea-ice covered areas. The relative magnitude of these sources remains poorly constrained in polar regions, which affects our ability to predict their impact on halogen chemistry, cloud formation and climate over the rapidly changing sea ice. We implement a blowing snow and a frost flower emission scheme in the GEOS-Chem global 3D chemical transport model, which we constrain with in situ observations of SSA mass concentrations at 5 polar sites. We find that the observed SSA concentrations are often overestimated during summer, when the polar ocean is characterized by cold sea surface temperatures and low salinities. We also find that inclusion of blowing snow or frost flower emissions increases the simulated SSA mass concentrations by factors of 2-10 during winter. The inclusion of blowing snow (frost flowers) increases submicron SSA emissions by a factor of 2-3 (by 20-50%) in polar regions. We find that SSA emissions from blowing snow are largest in regions where persistent strong winds occur over sea ice (East of Greenland, central Arctic, offshore of northern Alaska, the Ross Sea and the Weddell Sea), while emissions from frost flowers are largest where cold air temperatures, open leads and mild winds are co-located (Canadian Arctic Archipelago and coastal regions of Siberia, the Weddell Sea and the Ross Sea). Overall, in situ observations of mass concentrations of SSA suggest that blowing snow is likely to be the dominant SSA source during winter, with frost flowers playing a much smaller role. However, the in situ observations of SSA mass concentrations in polar regions are limited in time and space. Given the different predicted locations of these two sea ice source types, we will use multi-year observations of aerosol extinction over the Arctic and Antarctic from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument onboard the CALIPSO satellite to further constrain the relative contributions of blowing snow and frost flowers during winter. The CALIOP observations will be complemented by in situ surface observations of aerosol extinction. We will also optimize the parameterization of SSA emissions over the cold waters of polar oceans with these aerosol extinction observations as well as Aquarius observations of ocean salinity.