The title tells us that this poem is a portrait of a woman, so we should have a pretty good sense of who this woman by the end, right? Um...not really. "Portrait d'une Femme" ends with the line, "Yet this is you" (30), but we're not really clear what "this" means. The speaker doesn't describe the woman so that we can say, "OK, her name is Liza, she grew up in California, she's a bit shy but very funny, and she likes the color blue." Instead, we get a mishmash of the speaker describing what are probably her social interactions and possessions alongside various objects floating around on the sea. In fact, we even have a hard time distinguishing between straightforward description and pure metaphor. Clearly a conventional sense of identity doesn't work here; the poem shows us a very different process in determining and characterizing a person.
The speaker's empathy with the "femme" makes clear that the speaker is also a woman.
We can read the poem as a long list of images and experiences that belong somehow to the woman (her "great store" of "riches"), and yet the poem concludes by saying that nothing is quite her own. This suggests that the woman's most defining characteristic is her dissatisfaction – she constantly feels that she is lacking something.
"Portrait d'une Femme" moves between two settings: the Sargasso Sea and London. It alternates between chaotic, natural sea imagery and depictions of civilized urban life. Interestingly, both the sea and the city seem to be filled with rubbish, whether this takes the form of "Strange woods half sodden" (26) or "tarnished, gaudy, wonderful old work" (22). Somehow both the natural world and the manmade world associated with the woman become collection bins for debris and useless objects.
The speaker's association of the woman with the sea is part of a sexist tradition that associates women with the physical and natural (e.g., "Mother Nature"), while men are the civilized thinkers.
Although we intuitively think of the sea as part of the natural world, the poem actually depicts the sea as a place for commerce and cargo. The poem therefore suggests that the contrast between London and the Sargasso Sea is not so large.
Although "Portrait d'une Femme" is filled with vivid, concrete imagery of the sea and sea-bound cargo, the actual merchandise traded seems to be conversation, which is much more intangible and harder to price. The poem's ending is especially strange in this regard, since the speaker seems to go through a lot of effort to transform the products of conversation into valuable objects that can be possessed, only to decide at the end that all this is nothing, and certainly nothing that the woman can own. Make up your mind, man!
Lines 29 and 30 are essentially a single iambic pentameter line that has been split into two parts. This represents, formally, a breakdown in the speaker's own ability to communicate and properly express his thoughts about the woman.
Both conversation and sea cargo are elaborate metaphors for sexual favors. This is why the speaker describes the woman receiving a "fee" (3) and providing "strange gain" (15) to her visitors.
You can almost read "Portrait d'une Femme" as a long inventory, or laundry list. The speaker outlines a whole "sea-hoard" of different types of merchandise, both manmade and nature-made, tangible and intangible. Instead of describing the "femme" directly, the speaker focuses on the things exchanged between her and others. What do they pay her? What does she pay them? What riches does she store? The woman becomes defined by her surroundings and interactions with other people (men) rather than any essential qualities. The speaker concludes that there is nothing that's quite her own.
The "femme" is a very wealthy woman, but the speaker is trying to tell her that her wealth is useless, that other things are more valuable than money.
This poem criticizes the idea that a person can be defined by their possessions. It argues that a fixation on material wealth leads to the loss of an individual's true identity.