Then again the poem is a sequence but it's "about" war. It's about the ubiquity of war, in which every "there" is there. You can't turn away from it because it is just there. I don't try to get somewhere as a reader because in the end I will end up there, again.
The poet is pointing out things ("Look, there is that, and, see, over there is that...") and he is saying that these things are. It is also, in certain lines, about what is not there, not present (his love). So "there" on occasion means the opposite of presence.
The translation I know is by Michael Benedikt. The whole poem is in my English 88 site, and there--just below, there (see what I mean about thereness?)--are the first few lines and then a few others:
There is this ship which has taken my beloved back again
There are six Zeppelin sausages in the sky and with night
coming on it makes a man think of the maggots from which the
stars might some day be reborn
There is this enemy submarine slipping up beneath my love
There are one thousand young pinetrees splintered by the
bursting of the same shells falling around me now
There is this infantryman walking by completely blinded by
There are all these crosses everywhere this way that way
There are paradisial persimmons growing on cactus-trees in
There are the long hands of my love