Widespread And Unprecedented Phytoplankton Blooms Triggered By 2019–2020 Australian Wildfires

Droughts and climate-change-driven warming lead to more frequent and intense wildfires, arguably contributing to the severe 2019–2020 Australian wildfires. The environmental and ecological impacts of the fires include loss of habitats and the emission of substantial amounts of atmospheric aerosols. Aerosol emissions from wildfires can lead to the atmospheric transport of macronutrients and bio-essential trace metals such as nitrogen and iron, respectively. Previous works suggested that the oceanic deposition of wildfire aerosols can relieve nutrient limitations and, consequently, enhance marine productivity, but direct observations are lacking. Here we use satellite and autonomous biogeochemical Argo float data to evaluate the effect of 2019–2020 Australian wildfire aerosol deposition on phytoplankton productivity. We find widespread and long-lasting phytoplankton blooms in the Southern Ocean downwind of Australia. Aerosol samples originating from the Australian wildfires contained a high iron content, and atmospheric trajectories show that these aerosols were likely to be transported to the bloom regions, suggesting that the blooms resulted from the fertilization of the iron-limited waters of the Southern Ocean.