Abstract
Using oceanographic monitoring data（1996－2014）at the Okhotsk Tower, Mombetsu, Hokkaido, southwestern Okhotsk Sea,seasonal changes in oceanographic environments in the surface layer was shown, and the interannual variations in oceanographicenvironments and sea-ice concentration in coastal waters during winter and spring were analyzed. The climatological means of temperature in the surface layer reached a minimum in mid-February and a maximum in late-August. The climatological mean of
salinity in the surface layer was at a minimum（31．60）in early January, and was maintained at a relatively high value（33．0－33．5）between July-October. The climatological mean of chlorophyl（l Chl.）a concentration in the sea surface began to increase in March. After reaching a maximum（3．1mg m－3）in April, the Chl. a concentration was maintained at 1－2mg m－3 until November. The monthly means of concentration of nutrients decreased seasonally after the increase in Chl. a concentration ;however, the pattern of seasonal variation differed among nutrients. These characteristics in seasonal variation on these oceanographic environments observed in the surface layer around the Okhotsk Tower were generally similar to those in the coastal water off Mombetsu. The timing of the increase and decrease in sea-ice concentration in the coastal water off Mombetsu varied interannually, the timing of the decrease in sea-ice concentration differed by approximately1．5months between years between the
