Program: RESESS Boulder
Major: Geoscience & Chemistry
Academic Affiliation: University of Arizona
Mentors: Dr. Nikki Lovenduski
Shana Egan is a rising senior undergraduate student at the University of Arizona and is pursuing a dual-Bachelor’s in Geosciences and Chemistry. Through RESESS 2021, she helped with finding the consequent impact of the 1991 Mt. Pinatubo volcanic eruption on phytoplankton activity in the Pacific Ocean through CESM modeling. Her passions include natural hazards and their connection to public safety, both of which were sparked during her childhood in hurricane country: Florida. After graduation, she hopes to obtain a graduate degree in Geophysics and to later seek a career involving natural hazards.
Phytoplankton form the base of marine food webs and spatial and temporal variations in phytoplankton productivity can influence marine ecosystems and fisheries. Previous work has linked spatial and temporal variability in phytoplankton productivity to internal climate variability, such as the El Niño – Southern Oscillation, yet few studies have examined how external climate perturbations, such as volcanic eruptions, can influence phytoplankton productivity. The June 1991 eruption of Mt. Pinatubo had a large influence on the global climate system, reducing shortwave irradiance at the surface and cooling the planet. Here, we quantify the impact of the climate anomaly caused by this eruption on phytoplankton primary production using output from two sets of simulations of the Community Earth System Model: (1) an ensemble of simulations that includes aerosol forcing and radiative impacts associated with the eruption, and (2) an ensemble of simulations that excludes this forcing, but is otherwise identical to the first. We estimate the impact of the eruption on productivity by calculating the differences in the ensemble means from each set of simulations. Globally integrated phytoplankton productivity shows only small changes due to the eruption, though regional changes in productivity are apparent, especially in the tropical Pacific Ocean. The climate anomaly associated with the eruption caused large reductions in phytoplankton productivity in the eastern Tropical Pacific in 1992, likely due to eruption-induced El Niño-like conditions. The eruption also caused unexpectedly large productivity increases in the western Tropical Pacific during 1996 that significantly impacted global productivity. Our results provide perspective on how external climate forcing can impact the marine ecosystem in the years following a volcanic eruption.