Shana Egan


Years participated in RESESS: 2021


An Overview

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.