Very large ocean, very small amount of material. Miniscule impact.
Radiation leaving the bomb is safe after it reacts with matter in the way, as it will in short order. The worry is radioactive material being freed and traveling into the food chain or a person directly. Most of a hydrogen bomb is not very dangerous, U238 tamper, foam, lithium, so on. If the primary was present it would be a core of plutonium, very small in size, dependent on implosion to reach critical mass. Plutonium will burn in air, otherwise it is very much like lead, wouldn't corrode, dissolve or flake off to any great extent.
The environmental danger is slight, and explosion highly unlikely, nearing impossible.
Radiation leaving the bomb is safe after it reacts with matter in the way, as it will in short order. The worry is radioactive material being freed and traveling into the food chain or a person directly. Most of a hydrogen bomb is not very dangerous, U238 tamper, foam, lithium, so on. If the primary was present it would be a core of plutonium, very small in size, dependent on implosion to reach critical mass. Plutonium will burn in air, otherwise it is very much like lead, wouldn't corrode, dissolve or flake off to any great extent.
The environmental danger is slight, and explosion highly unlikely, nearing impossible.