I'd assume as an explanation as to why he's in the Blue Hole. SPOILERS:
There is a Glacial Area you unlock later in the game. Godzilla might have had Baas Island-the island he lives on with Little Godzilla-destroyed in a similar fashion to Godzilla vs. Destroyah-igniting uranium deposits on the island, causing him to absorb huge amounts of radiation. He's probably heading to the Blue Hole to cool off-the trailer showcases Burning Godzilla rising out of the water with noticeably less steam emitting off his body then in Godzilla vs. Destroyah, so clearly it's having an effect. As for where his radiation is going, there's a prehistoric hydrothermal vent area, presumably with higher radiation levels to support the life there, so his radiation could be discharging there and into the Divine Tree. Also, the Blue Hole has some big and unusual marine life-hermit crabs that carry freaking dumpster trucks rather than shells, for example-and if we're counting the Dredge DLC, a lot of aberrational fish. So Godzilla, in fighting those, can also discharge a lot of energy.