[A-CG42] Water and sediment dynamics from land to coastal zones

[ACG42-09] Long river plume around Akkeshi Bay formed by snowmelt runoff

*Satoshi Nakada¹, Tomonori Isada² (1.National Institute for Environmental Studies, 2.Hokkaido University)

Keywords:sea surface salinity, snowmelt runoff, river plume, colored dissolved organic matter, geostationary ocean color satellite

This study investigated the seasonal variation in the river plumes formed in the coastal sea around Akkeshi Bay, Hokkaido, using a sea-surface salinity (SSS) map estimated from the colored dissolved organic matter (CDOM) product derived from the geostationary ocean color imager, GOCI-COMS. Focusing on the high correlation relationship between the CDOM and the SSS in the sea surface water, we developed a estimation method of the SSS maps from the CDOM data of high-resolution (500 m) and high-frequency (8 times a day) GOCI-COMS products in eight times a day based on the results of field observations and water sampling obtained in Akkeshi Bay. We analyzed the SSS maps created in 9 years from 2012 to 2020, and found that the remarkably large river plume was formed in the coastal sea around Akkeshi Bay during the snowmelt season from March to April every year. This river plume was a part of the long river plume that developed in coastal ocean and elongated from off Cape Erimo in the south to off Cape Nosappu in the east. This river plume shrank in the summer in phase with the increase of the SSS. This inferred that the snowmelt runoff occurred in the spring could form the river plumes in estuaries located along the coast, and coalesce into the long river plume.