It's absolutely pitch black, because photons cannot reach the average depth of the ocean, which is 12,000 feet. In the Rift Valley, it's 9,000 feet.
ここは漆黒の闇です　なぜなら 光子は約4000メートルという平均海底深度まで 達しないのです　地溝帯は約3000メートルあります