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

Andra Whiteside, Cecile Dupouy, Awnesh Singh
Philipson Bani, Jing Tan and Robert Frouin

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.
KEYWORDS
chlorophyll-a (Chl-a), HTHH, light attenuation, particle backscattering, ocean
currents, volcanic ash, remote sensing
Frontiers

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