5:15 PM - 6:45 PM
[AOS13-P06] Relation Between Eruption at Nishinoshima and Chlorophyll-a Concentration at Ogasawara Islands in June-August 2020
Keywords:Chlorophyll-a Concentrations, Seasonal-Trend Decomposition Using Loess (STL), Volcanic Ash
Deposition of substantial ash from volcanic eruptions or wildfires into the sea induces rapid proliferation of marine phytoplankton for a short period [e.g., Tang et al., 2021]. Nishinoshima, located approximately 930 km south of Tokyo, has experienced intermittent vigorous volcanic activity since 2013. Simultaneous seawater discoloration around Nishinoshima was observed during the eruptions [e.g., Ono et al., 2018]. One proposed factor for this phenomenon is the increased phytoplankton due to volcanic ash. During the volcanic period from June to August 2020, it has been pointed out that the increase in satellite-derived chlorophyll-a concentrations (Chl-a), an indicator for dense phytoplankton, is related to the direction and composition of volcanic ash emissions [Kelly et al., 2023].
From Himawari-8 satellite data, we observe an increase in Chl-a around Muko-jima, located approximately 130 km northeast of Nishinoshima, from June to August 2020. We hypothesize that the volcanic ash from Nishinoshima promoted phytoplankton growth as it drifted by ocean currents to Muko-jima. In this study, we conducted Seasonal-Trend decomposition using Loess (STL) on Chl-a data in the Muko-jima vicinity and performed streamline tracking simulations at locations with increased Chl-a to investigate the cause of the Chl-a increase around Muko-jima.
Confirming the Chl-a increase around Muko-jima was not seasonally driven, we applied STL to Chl-a data obtained from the MODIS on the Terra and Aqua satellites, covering the region between 27.5°-27.7°N and 142.0°-142.2°E around Muko-jima from 2002 to 2023. The results showed significant residuals during the reported volcanic activity in June-July 2020. Since the supply of nutrients due to volcanic activity is expected to be a short-term phenomenon, volcanic effects are anticipated to appear as residuals in the STL decomposition. Therefore, the increase in Chl-a in June-July 2020 was demonstrated to be non-seasonal and possibly linked to volcanic activity.
To investigate the cause of the Chl-a increase around Muko-jima, we perform the streamline tracking simulations for representative points where Chl-a increased. We use the ocean current data from the Hybrid Coordinate Ocean Model GOFS 3.1 for the simulations.
We set the representative points at every 0.05° in the region between 27.5°-27.7°N and 142.0°-142.2°E around Muko-jima, where high Chl-a concentration was observed on July 6th, 2020. Additionally, we detected the spread of volcanic ash through Ash RGB images with Himawari-8 satellite data. The results showed that most of the representative points passed through the area approximately 72 to 143 km northeast of Nishinoshima, where volcanic ash spread at 18:00 on June 28th. Also, they indicated the Chl-a increase around Muko-jima was not due to the local flow from the vicinity of Nishinoshima. Therefore, the Chl-a increase around Muko-jima should be caused by volcanic ash from the Nishinoshima eruption, leading to the proliferation of Chl-a, which then reached the waters around Muko-jima through ocean currents. In addition to the above results, we discuss the causes of the Chl-a increase around Muko-jima from June to August 2020.
From Himawari-8 satellite data, we observe an increase in Chl-a around Muko-jima, located approximately 130 km northeast of Nishinoshima, from June to August 2020. We hypothesize that the volcanic ash from Nishinoshima promoted phytoplankton growth as it drifted by ocean currents to Muko-jima. In this study, we conducted Seasonal-Trend decomposition using Loess (STL) on Chl-a data in the Muko-jima vicinity and performed streamline tracking simulations at locations with increased Chl-a to investigate the cause of the Chl-a increase around Muko-jima.
Confirming the Chl-a increase around Muko-jima was not seasonally driven, we applied STL to Chl-a data obtained from the MODIS on the Terra and Aqua satellites, covering the region between 27.5°-27.7°N and 142.0°-142.2°E around Muko-jima from 2002 to 2023. The results showed significant residuals during the reported volcanic activity in June-July 2020. Since the supply of nutrients due to volcanic activity is expected to be a short-term phenomenon, volcanic effects are anticipated to appear as residuals in the STL decomposition. Therefore, the increase in Chl-a in June-July 2020 was demonstrated to be non-seasonal and possibly linked to volcanic activity.
To investigate the cause of the Chl-a increase around Muko-jima, we perform the streamline tracking simulations for representative points where Chl-a increased. We use the ocean current data from the Hybrid Coordinate Ocean Model GOFS 3.1 for the simulations.
We set the representative points at every 0.05° in the region between 27.5°-27.7°N and 142.0°-142.2°E around Muko-jima, where high Chl-a concentration was observed on July 6th, 2020. Additionally, we detected the spread of volcanic ash through Ash RGB images with Himawari-8 satellite data. The results showed that most of the representative points passed through the area approximately 72 to 143 km northeast of Nishinoshima, where volcanic ash spread at 18:00 on June 28th. Also, they indicated the Chl-a increase around Muko-jima was not due to the local flow from the vicinity of Nishinoshima. Therefore, the Chl-a increase around Muko-jima should be caused by volcanic ash from the Nishinoshima eruption, leading to the proliferation of Chl-a, which then reached the waters around Muko-jima through ocean currents. In addition to the above results, we discuss the causes of the Chl-a increase around Muko-jima from June to August 2020.