Fig. 6

Relationship between dissolved iron (dFe) concentrations, time lagged annual air temperature (Ta), and discharge. a Late summer (July, August, and September; JAS) dFe concentrations in the Amur River and Ta with a 7-year lag in the NE-Amur; b late spring (April, May, and June; AMJ) dFe concentrations and Ta with a 9-year lag in the NE-Amur; c late summer dFe concentrations and discharge; d late spring dFe concentrations and discharge. Only Ta in the NE-Amur is shown because the Pearson’s coefficient between Ta and dFe in the NE-Amur is higher than that in NW-Amur and that in S-Amur (Fig. 5a–c). In a and b, seasonal mean dFe concentrations are shown. In c and d, individual measurements of dFe concentration and discharge are shown. In c, the black circle denotes the data in 1997, which is the peak year of iron anomaly