Which ocean zone has the warmest water temperature

Epipelagic zone

Explanation:

Source of heat in oceans is the Sunlight. The sunlight zone of the ocean extends from the surface water to the depth of 200 m. It is also called the epipelagic zone. It is the zone of oceans which obtain maximum sunlight. The ample input of solar radiations in the epipelagic zone makes the its water warmest among all the zone of the ocean.

chordata is the answer

answer; i believe the answer is hydraulic action;