11:15 AM - 11:30 AM
[ACG53-09] Spatial Assessment of the Impact of Kuroshio Branch Intrusion on the Spring Phytoplankton Bloom in Kagoshima Bay Using GCOM-C SGLI
Keywords:Kuroshio, Satellite , Phytoplankton, SGLI
Kagoshima Bay is a semi-enclosed embayment influenced by the Kuroshio branch current, which plays a crucial role in the material circulation and ecosystem dynamics. However, the extent to which Kuroshio intrusions contribute to phytoplankton bloom formation and transport remains unclear. In this study, we examined two Kuroshio intrusion events observed in 2019 and 2020: a strong intrusion event (March 17–25, 2019) and a weak intrusion event (March 7–11, 2020). Using data from the Second Generation Global Imager (SGLI) satellite and ferry-based sea surface temperature (SST) observations, we evaluated how the intensity of Kuroshio intrusions affects the spatial distribution and dynamics of phytoplankton in Kagoshima Bay.
Analysis of SGLI-derived Chl-a and SST data revealed that the dynamics of phytoplankton in the bay differed significantly depending on the intensity of Kuroshio intrusions. During the strong intrusion event in 2019, Chl-a concentrations in the bay temporarily increased but subsequently declined due to rapid dilution at the bay mouth. Conversely, during the weak intrusion event in 2020, phytoplankton biomass continued to accumulate in the bay before eventually being transported outwards. Ferry-based SST observations showed that abrupt temperature increases exceeding 1°C/day occurred 3–7 times annually, serving as indicators of Kuroshio intrusions. Spatial autocorrelation analysis indicated that 45.4% of the bay, particularly the eastern part, exhibited significant positive correlation with variations at the bay mouth. Partial autocorrelation analysis further demonstrated strong correlations at both –5 days (when the bay leads) and +5 days (when the bay mouth leads), suggesting a 5-day periodicity in phytoplankton dynamics within the bay.
These findings demonstrate that the intensity of Kuroshio intrusions significantly influences the mechanisms driving phytoplankton bloom formation. Strong intrusions lead to rapid dilution at the bay mouth, suppressing bloom formation, whereas weak intrusions allow blooms to persist within the bay before being gradually transported outward. Furthermore, the formation and subsequent transport of phytoplankton biomass from the bay to offshore waters may contribute to the lower trophic production in the Kuroshio region. These insights are essential for understanding the ecological impacts of Kuroshio intrusions on coastal ecosystems and can provide valuable knowledge for coastal management and ecosystem modeling.
Analysis of SGLI-derived Chl-a and SST data revealed that the dynamics of phytoplankton in the bay differed significantly depending on the intensity of Kuroshio intrusions. During the strong intrusion event in 2019, Chl-a concentrations in the bay temporarily increased but subsequently declined due to rapid dilution at the bay mouth. Conversely, during the weak intrusion event in 2020, phytoplankton biomass continued to accumulate in the bay before eventually being transported outwards. Ferry-based SST observations showed that abrupt temperature increases exceeding 1°C/day occurred 3–7 times annually, serving as indicators of Kuroshio intrusions. Spatial autocorrelation analysis indicated that 45.4% of the bay, particularly the eastern part, exhibited significant positive correlation with variations at the bay mouth. Partial autocorrelation analysis further demonstrated strong correlations at both –5 days (when the bay leads) and +5 days (when the bay mouth leads), suggesting a 5-day periodicity in phytoplankton dynamics within the bay.
These findings demonstrate that the intensity of Kuroshio intrusions significantly influences the mechanisms driving phytoplankton bloom formation. Strong intrusions lead to rapid dilution at the bay mouth, suppressing bloom formation, whereas weak intrusions allow blooms to persist within the bay before being gradually transported outward. Furthermore, the formation and subsequent transport of phytoplankton biomass from the bay to offshore waters may contribute to the lower trophic production in the Kuroshio region. These insights are essential for understanding the ecological impacts of Kuroshio intrusions on coastal ecosystems and can provide valuable knowledge for coastal management and ecosystem modeling.