Shipborne Measurements of Mineral Dust and Black Carbon Aerosols over the Southern Ocean in the Austral Summer

Atmospheric mineral dust and black carbon (BC) aerosols play important roles in the Earth’s climate system, yet direct observations over the Southern Ocean (SO) are scarce. In this study, we present the characteristics of airborne water-insoluble particles collected during a cruise of the R/V Shirase in the Australian and Indian sectors of the SO from December 2022 to March 2023. Using a complex amplitude sensor, we measured complex scattering amplitude of individual water-insoluble particles. Based on the measured complex scattering amplitude, which depends on particle composition, size, and shape, we classified into dust-like (0.50–5.0 µm in diameter) and BC-like (0.15–0.50 µm in diameter) particles. The number (mass) concentrations of dust-like and BC-like aerosols were 0.013–9.2 L^-1 (0.52–32 ng m^-3) and 5.4–2.3×10² L^-1 (0.065–2.1 ng m^-3), respectively. For dust-like aerosols, the highest concentration was observed in a region closest to Australia in this cruise, indicating strong influence of the emission from mid-latitude continents. Furthermore, a sample collected nearest to the Antarctic coast exhibited relatively high dust-like aerosol concentrations than that collected in most offshore regions away from both mid-latitude and Antarctic continents, suggesting that the Antarctic continent might be a potential source of dust aerosols. For BC-like aerosols, their concentration showed a clear latitudinal gradient, decreasing with distance from mid-latitude sources even close to the Antarctic coast.