The Effects of Wildfire Aerosols on Phytoplankton Populations in the North Pacific Ocean

Abstract

Aerosols released by wildfires can have varying effects on phytoplankton populations. Although wildfire smoke can block sunlight and inhibit phytoplankton growth, wildfire aerosols also deposit phosphorus, nitrogen, and iron onto nutrient-limited oceans, providing a major food source for phytoplankton. Phytoplankton are critical to oceanic food webs, and fluctuations in phytoplankton populations could bring drastic changes to oceanic ecosystems. In this study, I explore relationships between aerosols emitted by intense California wildfires in 2020 and phytoplankton in the nearby North Pacific Ocean during this time. I analyzed chlorophyll-a, Photosynthetically Available Radiation (PAR), Aerosol Optical Depth (AOD), Particulate Matter under 2.5 micrometers (PM2.5), and nutrient data from satellites by creating climatologies, maps, and time series of these variables from 2003-2020. For July through November, PM2.5 emissions from wildfires and chlorophyll-a amount (an indicator of phytoplankton) were both highest in 2020, during the Giga Fire period, in the North Pacific compared to 18 years of previous wildfire seasons. Visual results display significant, positive deviations from climatological means in chlorophyll-a of up to 170% in September of 2020. This reveals anomalously high chlorophyll-a levels in the North Pacific Ocean following periods of wildfires, implying a large increase in phytoplankton populations. The existence of positive correlations between wildfire emissions and phytoplankton growth are demonstrated to be possible in this study, leaving immense implications for the dynamics of global aquatic ecosystems.