The co-occurrence of ash deposition with increases in chlorophyll concentration at Nishinoshima Volcano, Japan

Abstract

Nishinoshima is an ocean island volcano 1000 km south of Tokyo that has been erupting intermittently since 2013. In December 2019, an eruption at the island began that started as effusive, but six months later, the activity switched to primarily explosive until the middle of August 2020. It was during this explosive phase that increases in chlorophyll concentration were observed that spanned O(100 km). After the explosive activity at Nishinoshima ceased, these areas of heightened chlorophyll concentration ceased as well. We use aerial observations and satellite imagery to correlate these phytoplankton blooms in space and time with the explosive phase of Nishinoshima. We use fluorescence satellite remote sensing products to establish that these observed chlorophyll blooms were biologic in nature, making them phytoplankton blooms. Finally, we apply an understanding of the nutrients needed to supply phytoplankton blooms to suggest that blooms were of nitrogen-fixing phytoplankton. Overall, we provide a case study of fertilization of nutrient-poor ocean with volcanic ash and demonstrate a scenario where volcanic ash triggers extensive phytoplankton blooms.