Hydrosphere

The hydrosphere is the combined mass of water found on, under, and over the surface of a planet — oceans, rivers, lakes, groundwater, ice, and water vapor in the atmosphere. On Earth, it is the great thermal reservoir: the oceans absorb and store solar energy, moderating temperature extremes and driving the hydrological cycle that redistributes water across the globe. The hydrosphere is not passive. It actively exchanges energy, carbon, and nutrients with the biosphere and the geosphere, and its circulation patterns — from the thermohaline conveyor to tropical rainfall belts — are emergent structures of a fluid planet. Water is the solvent in which the Earth system's chemistry happens, and the hydrosphere is the vessel that holds it.