Hydrosphere



Hydrosphere in physical geography describes the combined mass of water found on, under, and over the surface of a planet.

On Terra, the hydrosphere is estimated to be 1386 million km3 of water. This includes water in liquid and frozen forms in groundwater, glaciers, oceans, lakes and rivers. Saline water accounts for 97.5% of this amount. Freshwater accounts for only 2.5%. Of this fresh water 68.7% is in the form of ice and permanent snow cover in the Arctic, the Antarctic, and in the mountainous regions. Next, 29.9% exists as fresh groundwater. Only 0.26% of the total amount of fresh waters on Terra is concentrated in lakes, reservoirs and river systems where they are most easily accessible for human's economic needs and absolutely vital for water ecosystems. The total mass of the Terra's hydrosphere is about 1.4 × 1018 tonnes, which is about 0.023% of the Earth's total mass. About 20 × 1012 tonnes of this is in Terra's atmosphere (the volume of one tonne of water is approximately 1 m3). Approximately 75% of Terra's surface, an area of some 361 million km2 (139.5 million square miles), is covered by ocean. The average salinity of the Earth's oceans is about 35 grams of salt per kilogram of sea water (3.5%).

Planetary hydrospheres in the Union range from absolutely zero on or in the planet to 100% surface area coverage. (See GWC 4F and ice planet .)