The Geochemistry of the Earth - Thanatia: The Destiny of the Earth's Mineral Resources - page 110

Table 5.3 Inventory of water at the Earth's surface (Pid-
wirny, 2006)

Volume, Mkm 3

Reservoir %

Oceans 1370 97.25

Ice Caps and Glaciers 29 2.05

Groundwater 9.5 0.68

Lakes 0.125 0.01

Soil Moisture 0.065 0.005

Atmosphere 0.013 0.001

Streams and Rivers 0.0017 0.0001

Biosphere 0.0006 0.00004

Sum 1408.71 100.00

hydrological cycle, which is a conceptual model that describes the storage and move-
ment of water between the biosphere, atmosphere, lithosphere and the hydrosphere
(see Sec. 6.6.2 for more details).
The planetary water supply is dominated by the oceans (see Table 5.3). In fact,
more than 97% of all water on Earth is contained within them. The other 3% is
held as freshwater in glaciers and icecaps, groundwater, lakes, soil, the atmosphere
and biosphere (Pidwirny, 2006). The greatest portion of freshwater (75%) is in the
shape of ice and permanent snow cover over the Antarctic, Arctic and mountainous
regions.
The remaining 25% referred to as renewable water exist as fresh and ground
waters. Only 0.33% of the total amount of freshwater is concentrated in lakes,
reservoirs and river systems (surface waters), which are not only the most accessi-
ble but also very important water ecosystems. Considered in its entirety, the Earth
has a comparatively stable water budget. Unfortunately most of it is overwhelm-
ingly salty. Furthermore, freshwater is not evenly distributed over land territories.
To compound matters, industrialisation and unsustainable land use practices are
dramatically increasing water pollution and thereby threatening the world's supply
of potable water.
In the following sections, the main water reservoirs of the Earth are analysed,
stressing their abundance, economic importance and chemical compositions.

5.4.1 Seawater

The oceans account for a little over 70% of the Earth's surface and comprise more
than 97% of the hydrosphere. The volume of water contained in the ocean is about
1:37 10 9 km 3 (Pidwirny, 2006). The Pacific Ocean is by far the biggest in the
world, followed by the Atlantic and the Indian oceans (see Table 5.4). Oceans
represent a relatively well-mixed system of considerable mass and potential com-
mercial use. The prime functions of the oceans are those related to atmospheric
behaviour. They constitute the only major source of atmospheric moisture for the
continents and serve as gigantic “energy cells” for the receipt, storage, and release
of the radiant solar energy that fuels the climate and weather. The thermohaline