In the first two lines of the poem, the poet uses—

In the opening lines 'Break, Break, Break, / On thy cold gray stones, O Sea!', the poet directly addresses the sea, an inanimate/non-human entity. This direct address to an absent person, abstract idea, or inanimate object is the literary device called apostrophe. The 'O Sea!' construction is a classic example of apostrophe. Hence (2) is correct.