Submersibles and ROVs have allowed closer study of the ocean depths, and oceanographers have not found any Eldritch Abomination or Cthulhu in any part of the sea-floor (yet). Creatures spawned before The Great Flood might be swimming down there, torpid and undisturbed - not disturbed yet, at least.

Great strange beasts that have not set foot on the shore since prehistory might be silently stomping across the silty seafloor. Some surmised that the ocean depths were a sort of Lost World where monsters that had ages ago vanished from the surface could still be alive and hiding. Oceanographers had almost no information to work with, and Nothing Is Scarier. No ray of light can reach that depth, and Dark Is Evil. Until recent technological developments, no one had a chance at observing the deep sea. The ocean floors and trenches have forms of life that are wholly alien to humans: deep sea anglerfish, Giant Squids, gulper eels, chimera fish, to which fiction can add any bizarre variety of horrific leviathan. The really deep, dark parts of the ocean are even more mysterious. We know more about the surface of Mars than we do about our own oceans.

Terraria how to survive the abyss