I need help whith this Gull, is't possibly a Atlantic Gull L.m.atlantis ?

Probably a very dark 2 cal. year Herring, ssp.argenteus. The rump in atlantis would have broader dark pattering, and generally hindneck and flanks would again show more extensive dark pattern.
The individual variation in Herring is large, so safe ID of an out of range atlantis is at best very difficult.

The picture in the last link obviously shows fresh second generation tertials and greater coverts, which would be rather unlikely for a Herring Gull in early May...

Also noted the second generation tertials and some of the coverts - which as Ruud say´s would be unusual for Herring at this age and time of year - but then again perhaps not entierly impossible. It doesn´t strike you as either a michahellis or atlantis (apart from moult), atlantis for the reasons mentioned by KMO together with rather pale inner primaries. The hybrid theory comes to mind here. In the image with the LBBG scapulars looks rather pale grey.

JanJ

IMO argenteus can be ruled out by the absence of an obvious pale window on the inner hand alone, but also shape of head and bill and of course moulted wing coverts (not replaced randomly as seen in a small portion of Herring) are contra this taxon. Some Baltic argentatus may strongly resemble YLG but the chance that such birds would reach Iceland seems very slim.

I have received other images from the photographer as well. Structurally it looks like a YLG, but any replaced tertials en wing coverts are very unlikely to look this fresh in the nominate form. I have no experience with atlantis but given the resemblance to LBBG I think this could very well be one.