When we say in the Arctic ocean, "the" is used so is Arctic a "noun" there? The Arctic is a noun, Arctic ia an adjective?

Probably not, Arctic is probably an adjective. But "Arctic Ocean" may be a proper noun. The big bear ran after the little mouse. "Big" and "little" are adjectives, not nouns.

It is a proper name in this case, so a noun.  The same word can be used as an adjective, though.  arctic conditions in the Arctic Ocean.

Many -ic words are both nouns and adjectives and which they are is dependent upon how they are used: psychotic, prolific, mafic, horrific, pneumatic.  Usually, the noun form is a generalization from the adjective form, a noun made from an adjective (rather than the reverse).

The psychotic are not usually concerned with the feelings of others.  The psychotic patient required medication to control his behavior.  A pneumatic pump operates from compressed air; pneumatics are common devices used in situations with explosive hazards.  Mafic igneous intrusions are low in silica.  The absence of visible quartz is a good way to identify mafics.