Impact of ashes from the 2022 Tonga volcanic eruption on satellite ocean color signatures

Abstract

A powerful eruption within the Hunga Tonga-Hunga Ha’apai (HTHH) volcano (20.64°S, 175.19°W) in the Kingdom of Tonga, occurred on 15 January 2022. The volcanic blast was enormous, leading many scientists to investigate the full impact and magnitude of this event via satellite observations. In this study, we describe a new ocean color signature from a discolored water patch created by the HTHH eruption using NASA and CMEMS products of satellite-derived biological and optical properties. Elevated surface chlorophyll-a concentration (Chl-a) between 0.15 to 2.7 mg.m-3 was not associated with phytoplankton growth, but to basalt-andesitic ash material expelled by the volcano and into the ocean, which resulted in erroneous Chl-a estimates. Distribution of the patch over time was aligned with CMEMS ocean currents for 19 days. The gradual decrease of light attenuation or diffuse attenuation coefficient for downward irradiance at 490 nm, Kd(490), was interpreted as due to the sinking of ash particles with time. It is suggested that due to high porosity of 30-40%, a density close to that of seawater, ash particles stay suspended in the water column for more than 10 days with sustained high values of satellite-derived Chl-a, Kd(490), and particulate backscattering coefficient at 443 nm. The high attenuation of light due to ash, reducing the penetration depth to less than 10 meters during the first period after the eruption may have had implications on ecological processes and biogeochemical cycles in Tongan waters.