this and other questions of the sea, scientists seek answers with full awareness much
about the oceans is not fully understood.
- Sea water is a weak, but complex solution made up of many
things including mineral salts and decayed biologic matter from marine organisms.
- Most of the ocean's salts are derived from gradual processes,
such as weathering and erosion
of the earth's crust and mountains by the dissolving action of rains and streams.
Some of the ocean's salts have been dissolved
from rocks and sediments below the sea floor, while others have escaped from the
Earth's crust through volcanic vents as solid and gaseous materials.
Salts become concentrated in the sea because
the Sun's heat
evaporates almost pure water from the surface of the ocean, leaving
the salts behind. This
process is part of the continual exchange of water between the Earth and
called the hydrologic cycle, which, along with the sources
of salt, is illustrated in the following diagram.
Water vapor rises from the ocean surface through evaporation
and is carried landward by the winds in the form of clouds and humidity.
When the vapor in the clouds collides with a colder mass of
air, the moisture condenses (changes from a gas to a liquid) and falls to Earth as rain.
The rain runs off into streams, or underground
as groundwater, both of
which transport water back to the sea.
Evaporation from both the land and the ocean again causes
water to return to the atmosphere as vapor and the cycle starts anew.
Natural products like dissolved salts are
not the only chemicals that are transported by rivers to the sea.... Listen to Seaweb's Ocean Report for a short
discussion on non-point source pollution of our coastal regions.