There are two proposed mechanisms for the influence of latitude on the δ15NPOM. One is the Japanese territorial influence. The other is the impact of the coastal branch of the Tsushima Warm Current. The coastal branch of the Tsushima Warm Current originates from the eastern channel of the Tsushima Strait and flows along the Japanese coast (Katoh, 1994). Our monitoring regions always included a coastal region in the low latitude area, as well as flows of the coastal branch of the Tsushima Warm Current (Katoh, 1994). The δ13CPOM did not indicate direct territorial inputs in this case, thus the influence of the coastal branch of the Tsushima Warm Current and the origin of the waters may be the explanation.