Where does “北極洋” come from?

北極洋 (Japanese) comes from Japanese 洋, from Middle Chinese 洋.

Ancestry of “北極洋”, step by step

北極洋 traces back through two separate lines of ancestry.

via Japanese

StepLanguageWordMeaning
1Japanesean ocean; the East or "especially" the West;...
2Middle Chinese

via Japanese 北極

StepLanguageWordMeaning
1Japanese北極Short for 北極圏. north polar region, north pole;...
Every word from Middle Chinese Every word from Japanese
北極洋 — Etymology, Origin & Word History | Etymology Explorer