Instrumental for genitive construction

Question

In a poem by Anna Akhmatova, we read:

В таком году произошло бы то-то,
А в этом — это: ездить, видеть, думать,
И вспоминать, и в новую любовь
Входить, как в зеркало, с тупым сознаньем
Измены и еще вчера не бывшей
Морщинкой…

It was translated by Judith Hemschemeyer as follows:

In this year, such and such would have happened,
In that year - that: traveling, seeing, thinking
And remembering, and entering into a new love
As into a mirror, with dim awareness
Of betrayal and of the wrinkle
That wasn't there the day before.

I don't understand why we have морщинкой and not морщинки. Indeed, морщинкой is instrumental while измены is genitive: I would have expected the genitive because I thought измены and морщинкой should be instances of а genitive construction of сознаньем (like the translation "betrayal" and "wrinkle" are genitive constructions of "awareness"). So, my question is: why do we have морщинкой and not морщинки?

Answer 1

The translation doesn't convey the Russian meaning precisely.

Literally, it's "to enter into a new love, as into a mirror, with dull awareness of infidelity and a wrinkle that wasn't there the day before". It's "enter with a wrinkle", not "enter with awareness of the wrinkle".

Морщинкой, as well as сознаньем, are in the instrumental because that's what the preposition с governs when it means with.