What is the tone in the poem, O Captain! My Captain!?

His tone is generally solemn and respectful though punctuated with moments of deep pain, such as when he exclaims “But O heart! heart! heart!” and describes it “bleeding drops of red,” describes his “mournful tread,” or arrives at the bleak and heavy image of his Captain “Fallen cold and dead” at the end of every stanza (5-24).