Coastal Oyashio South of Hokkaido, Japan

Abstract

Coastal Oyashio Water (COW), the cold low-salinity water lying along the southeast coast of Hokkaido, sometimes flows into Funka Bay on the southwest coast in winter and spring. Because this water is low in density, a density current called the ?Coastal Oyashio? was assumed to carry COW along these coasts. However, water property maps for April 1989, February 1992, February 1994, and February 1989 show that only for the latter month did COW extend as far west as Cape Erimo on the southwest coast. Steady-state flows were calculated using a baroclinic model and the density data collected in April 1989. Model results show that the Oyashio carries COW southwestward along the continental slope southeast of Hokkaido. It bifurcates south of Cape Erimo with a coastal portion turning around the cape but not always reaching the southwest coast because of the density structure along that coast. When the Oyashio crosses isobaths, the joint effect of baroclinicity and bottom relief (JEBAR) causes a barotropic flow to form a countercurrent on the southeast coast and eddies south off Cape Erimo and east off Tsugaru Strait. The countercurrent and the eddies are seen shoreward of the main current and downstream of the maximum JEBAR region. Thus, this model shows that the coastal Oyashio does not flow as a density current along the southeast coast. High-resolution SST maps collected in spring show eddies south of the cape, and confirm the model results. It is suggested that COW could be driven westward along the southwest coast by the northeasterly winds on the southeast coast.