Publication Date

Summer 2022

Degree Type


Degree Name

Master of Science (MS)




Carlie Pietsch


biological oceanography, Foraminifera, organism productivity, Shannon diversity, submarine caldera, Wilcoxon test, XRF

Subject Areas



Submarine volcanoes contribute more than 75% of global volcanic eruptions annually and have the potential to change the surrounding submarine ecosystems. The species richness, abundance of foraminifera assemblages and the average test size of samples recovered from marine sediment cores are a proxy for past environmental changes on the seafloor and in the water column. This study evaluates the ecosystem impact of multiple eruptions that formed a massive caldera at Axial Seamount between 1300 and 800 years before present (BP). An examination of the diversity, abundance, and size of planktic and benthic foraminifera assemblages recorded in volcanic and hemipelagic sediments deposited over the last 2300 cal. yr. BP, spans the eruptive history at Axial Seamount before, during and after the caldera-forming eruptions. The results of this study indicate that a unique benthic foraminifera fauna thrived during the 500-year caldera-forming eruption interval with significantly smaller test size, possibly in response to harsh chemicals in the water column near the seafloor. Planktic foraminifera communities experienced no significant change in diversity or size throughout the 2000-year study interval. Benthic and planktic foraminifera communities are the most diverse, most abundant, and the benthic assemblages are significantly larger in the uppermost samples at Axial. Bioavailable nutrients released from volcanic fluids could be responsible for the accumulation of more diverse foraminifera communities compared to pre-caldera sediment accumulations.

Available for download on Thursday, April 11, 2024