[A-OS21] Coastal ocean circulation and material cycle

[AOS21-P03] Coastal upwelling along the coast of Mainland Japan investigated with ROMS

*Hikaru Yanagisawa¹, Eiji Masunaga¹, Yusuke Uchiyama² (1.Ibaraki University , 2.Kobe University)

Keywords:ROMS, coastal upwelling, nutrient transport, mixed-layer depth

Coastal upwelling is known to occur along coasts when seasonal wind blows along the coast, leading to decrease in surface water temperature and increases in nutrients, which significantly influences the marine environment and fisheries. This study aims to understand processes of coastal upwelling and its effects using the regional oceanic modeling system (ROMS) around Japan. During the summer, surface water temperature frequently decreases 3 degrees in coastal areas, especially along the eastern coast of Japan, on days when southerly wind dominates. By calculating the correlation coefficient between the southerly wind stress and temperature difference from previous day for each grid, significant negative correlations appeaser along the east coast of Mainland Japan and Izu Peninsula suggesting a strong tendency for coastal upwelling. Cold water transport NO₃ from deeper regions toward the sea surface, leading to increase in phytoplankton near the surface. While the mixed-layer depth is several meters under weak wind conditions, it reaches 10–15 meters during upwelling events under enhanced southern wind conditions. When enhanced northerly winds blow, the surface temperature also drops by approximately 1 degree due to vertical mixing. During coastal upwelling events, combined effects of advective vertical water transport and wind-induced diffusive mixing near the surface may cause surface water temperature.