Page 66 - (DK) Ocean - The Definitive Visual Guide

64 CIRCULATION AND CLIMATE

The Global Water Cycle GLOBAL WATER FLOW

Water enters the atmosphere mainly as a result
of evaporation from the oceans and transpiration
THE WORLD’S OCEANS DO NOT FORM a self-contained system but continually by plants. It condenses to form clouds and falls
as rain and snow. On land, water moves downhill
exchange water with the atmosphere and landmasses through evaporation,
in rivers and glaciers. It soaks into the soil and
cloud formation, precipitation, wind transport, and river flow. This complex rocks, and is stored in lakes and wetlands.
of interconnected processes, which is ultimately driven by heat from the Sun, snow falls when
is called the global water cycle or hydrologic cycle. The cycle is made up of moisture in cold
air freezes at high
many smaller cycles, such as the formation and melting of sea-ice. altitude
snow and ice
accumulate
on high
mountains
clouds form as
rising air cools
and the water
vapor it holds
condenses
water returns to land
as rain when moisture-
winds blow carrying clouds cool
evaporation of moisture-laden in summer, snow and
water from ocean, clouds inland ice melt, releasing
driven by solar release of water fresh water
heating by plants through
transpiration

rivers steadily
evaporation of transport water
moisture from the towards the ocean
ground as a result
of solar heating
eventually,
downhill flow
means rivers flow
into the oceans

ocean water is below a line known water collects in water can flow cracks and holes
salty because it as the water table, hollows in the downhill underground in the rocks allow fresh
contains dissolved the rock is saturated ground, forming as well as above them to be filled water
nutrients with water freshwater lakes ground with water ocean water 3.5%
97%
atmosphere and
Earth’s Water Reservoirs other 0.09%
surface fresh
Just under one-third of a billion cubic miles (1.4 water 0.3%
billion cubic kilometers) of water exists on Earth.
About 97 percent of this water is stored in the oceans groundwater
30.1%
as a component of salt water. The rest is fresh water.
Of this, more than two-thirds is in the form of ice, rivers 2%
locked up in the vast ice-sheets that cover Antarctica
and most of Greenland, and in icebergs and sea-ice. wetlands ice 69.5%
INTRODUCTION PLAYERS IN THE CYCLE 1 part in 2,000) is water vapor in the atmosphere. RELATIVE SIZES SURFACE
EARTH’S
Much of the rest is groundwater—contained in
11%
WATER
underground rocks—while a tiny amount (less than
lakes 87%
Fresh liquid water on the Earth’s land surface, in lakes,
FRESH
wetlands, and rivers, makes up just 0.3 percent of all
WATER
the world’s fresh water, or 0.02 percent of the total
water. The Earth’s different water reservoirs have not
FRESH WATER
always had the same relative sizes that they have today.
The sea, ice, mountains, and clouds all play
Earth’s ocean water (the bulk of the rear cylinder, above)
For instance, during the ice ages, a higher proportion
a part in the global water cycle. This coastal
hugely exceeds its reservoirs of fresh water, and the relative
was locked up in ice, with less in the oceans.
proportion of fresh water found on the land surface is tiny.
scene is near Port Lockeroy in Antarctica.