It's a prepositional phrase but it's being used adverbially. Does that work for you?
No it does not. It does not seem to me to be being used in an adverbial way. My initial reaction to this was more of a gut response, but I consulted a grammar reference that pointed out a rule to the effect that a preposition without an object can be an adverb, while a preposition with an object is just a garden variety preposition.
Hence in the command "Go inside,"
inside is an adverb according to this rule. But in the command "Color inside the lines,"
inside is not an adverb because it has an object. I argue that the Latin expression
in situ carries with it its own object,
situ, and is therefore not an adverb, or least does not appear to be. AWAD provided the usage as "The sound engineers came to record the nuns in situ." It seems to me that
in situ here is analogous to any of the following prepositional phrases, all of which have objects:
1. The sound engineers came to record the nuns at the convent.
2. The sound engineers came to record the nuns in the sanctuary.
3. The sound engineers came to record the nuns in the cloister.
I can't think of a way that
in situ could be used in a way that is analogous to saying "Sit down" or "Take off," but I'm open to the possibility.
As an aside,
in situ is generally used as an adjective, as in the difference between
invasive ductal carcinoma and
ductal carcinoma in situ, or the difference between
in situ testing and
laboratory testing. If you re-wrote the AWAD usage example as "The sound engineers performed an
in situ recording of the nuns," then the expression
in situ clearly modifies the noun recording and not the verb to perform.
Finally, I find the above rule regarding the presence or absence of an object to be stupid. It really fails to distinguish between an implied object and the true absence of any object. If someone says "Go outside!" they clearly mean "Go outside the building in which you are currently located." To say that outside is modifying the verb in the way of a garden variety abverb like quickly is to cast a wide net regarding what constitutes an adverb. It seems much more logical to simply ask if the prepositional phrase really tells us something about how the verb is being acted out. For example, take the following two sentences:
1. Bob waited for the elevator with a heavy heart.
2. Bob waited for the elevator to the flight deck.
In #1, the prepositional expression modifies Bob's act of waiting. There's an object but
with a heavy heart is a figure of speech that modifies the verb here. It is along the same lines as saying that he waited anxiously, or that he waited nervously. In #2, the prepositional phrase clearly modifies the elevator, not Bob's act of waiting.
