I hardly believe you can keep a buoy anchored to a 5 kilometers deep seabed, in the middle of the ocean.

Ah, in the talk page https://en.wikipedia.org/wiki/Talk:Null_Island somebody else have the same doubt :)

tried to find it in https://webapp.navionics.com but it's hard due to missing lat/long, maybe somebody can make it https://webapp.navionics.com