Different values S3

I have downloaded one image from eumetsat Sentinel 3 Level 2.

I have reprojected and subsetted it.

I open the same band (CHL_NN) from arcmap and snap.
However, I see different values e.g. negative values in arcmap which in snap don t exist
why is that?

Attach screenshot.

Reprojection is not needed before or after subsetting. You can check statistics in SNAP and to see if all values, and not only the ones in the color palette, are more similar to the ones in Arcmap (Analysis/Statistics). You could also check what is the value of the NaNs (cloud and land masks) in Arcmap. We cannot really help with Arcmap issues.