Elihu speaks of the deep parts of the sea as if the sea were a plant and its depths were its roots. Possible meanings are 1) although the lightning causes light in the sky, the deep parts of the sea remain dark. AT: "but the depths of the sea remain dark" or 2) the lightning in the sky cause even the depths of the sea to have light. AT: "and lights up the depths of the sea" (See: [[rc://en/ta/man/translate/figs-metaphor]])