Connotation is defined as...
...suggestions and associations which surround a word as opposed to its bare, literal meaning. […] Connotation refers to qualities, attributes, and characteristics implied or suggested by the word and depends upon the context in which the word is used.
So connotation deals with associations, but they are figurative in nature, not literal—as is the case with all figurative language (e.g., metaphors, similes, hyperbole, etc.) It is used in literature.
Denotation is the opposite, and is used with science and philosophy. This, then, is literal. It is defined as "the dictionary definition of the word." Looking at an enormous group of people, ocean can be used to define the size of something, though the comparison itself is figurative.
In poetry, because it is so subjective by nature according to how the reader perceives it (based on one's attitudes and experiences), these are my personal perceptions.
In Maya Angelou's powerful poem, "Still I Rise," the author uses a metaphor when she states, "I'm a black ocean…" As metaphors are a form of figurative language, we understand that she is not literally an ocean, but she shares some of the same characteristics. Like an ocean, she is ever moving; nothing can stop her. She is also...
...leaping and wide,
Welling and swelling I bear in the tide.
Also like the ocean, her reach is broad and energetic ("leaping"), growing and moving, bringing something new as each wave in the ocean does. A wave can never be the same twice. She represents a powerful movement of the black race that will not apologize for its existence, but is coming into its own with an attitude of survival and triumph. She is the generation that, regardless of what a resisting society might try to do, is self assured and strong. And she pays homage to those once enslaved.
Bringing the gifts that my ancestors gave,
I am the dream and the hope of the slave.
She is, figuratively, a collection of all the experiences of her ancestors, but the best of them: their dreams and hopes.
Like an ocean, she is vast and wide, encompassing an area of change and growth that cannot be contained—forever moving forward. The connotation of "black ocean" refers to the black race of the past and present: countless slaves and people of color who have been victims of oppression and injustice. She speaks for those who have gone before her and those who have no voice. Figuratively, she represents all of them. The poem is not about "I," but about "we" and "them."
As denotation, "black ocean" refers singularly and simply to the black race as a whole.