Dolphins swim in the Hydrosphere.
(1). Hydro means the seas, ocean, bodies of water, glaciers, icebergs, etc.
(2). Magneto means area of space that is near the Earth that has charged particles that are controlled by a sort of magnetic field.
(3). Litho means the rigid of the outer part of Earth, that has the crust and upper mantle.
(4) Atmo means envelope of gases that is surrounding the Earth.
So the best option to pick Hydrosphere~
I hope this is what you are looking for~
