Dear Marton
Nice picture - it is difficult to get good pictures at sea! I wonder if you got any pictures showing some of the underpart of this bird? The reason I ask is that this bird makes me think Great-winged Petrel eg. big head and stout black bill, somewhat more brownish colour, a hint of a dark facemask and brighter areas at the billbase and throat. Great birding in those South-Atlantic waters!! - I was there myself some years ago when I saw both species.
The best birding-wishes
Allan

Dear Allan,
Thanks for the appreciation, yes it was indeed a nightmare to get more or less sharp pictures at the sea, just like to get good/true colors. I've uploaded a few other pictures about Atlantic petrels, I've also saw the Great-winged as well, but not as south as this one, we were already quite close to the antarctic convergence.
All the best,
Marton