1 Introducing Sea Water
1.1 Water on Earth
The general term fluid describes both gases and liquids. They both do not
have a definite shape and vessels are needed to contain them. A liquid has
a definite volume and a free surface, which is horizontal when the fluid is at
rest. In contrast, gases do not have a definite volume and will expand to fill a
container enclosing them. Solids are substances which are considered to have
both a definite volume and shape.
The most important liquid on Earth is water. Water is a ubiquitous, lifesustaining substance covering 71% of the Earth surface. Of the total Earth's
water content, some 97.2% is contained in the oceans, 2.15% is stored in ice
sheets and glaciers, 0.62% is a ground water, and only 0.03% flows through
rivers, streams and fresh-water lakes (Strahler and Strahler, 1992). For major
portions of the Atlantic, Pacific and Indian oceans, the average depth is nearly
4 kilometres, but it is the surface water, together with the very small amount
of ground water, that supports all life on the lands and in the oceans.
Depending on the temperature, water can exist as a liquid, a gas (water
vapour) or a solid (ice). Although existing in all three phases, the total volume
of water in the atmosphere, on the land, and in the oceans remains essentially
constant over time. However, waters of the oceans, atmosphere, and lands
move in a great and continuous cycle known as the hydrologic cycle (see
Fig. 1.1).
Evaporation from the oceans, which are the basic reservoirs of free water, is
approximately 419,000 km 3 /year, while evaporation from soil, plants and water
on the continents is only about 69,000 km 3 /year. The total quantity of the
evaporated water, 488,000 km 3 /year, must be returned annually to a liquid or
solid state through precipitation over the oceans and continents. Precipitation
over continents is about 37,000 km 3 /year larger than evaporation. This excess
of quantity flows over or under the ground to reach the sea. Because of the
cycling of water, freshwater is a 'renewable' resource in the sense that supplies
of freshwater are constantly renewed by rainfall over the land and ocean.
S. R. Massel, Fluid Mechanics for Marine Ecologists
© Springer-Verlag Berlin Heidelberg 1999
1.1 Water on Earth
The general term fluid describes both gases and liquids. They both do not
have a definite shape and vessels are needed to contain them. A liquid has
a definite volume and a free surface, which is horizontal when the fluid is at
rest. In contrast, gases do not have a definite volume and will expand to fill a
container enclosing them. Solids are substances which are considered to have
both a definite volume and shape.
The most important liquid on Earth is water. Water is a ubiquitous, lifesustaining substance covering 71% of the Earth surface. Of the total Earth's
water content, some 97.2% is contained in the oceans, 2.15% is stored in ice
sheets and glaciers, 0.62% is a ground water, and only 0.03% flows through
rivers, streams and fresh-water lakes (Strahler and Strahler, 1992). For major
portions of the Atlantic, Pacific and Indian oceans, the average depth is nearly
4 kilometres, but it is the surface water, together with the very small amount
of ground water, that supports all life on the lands and in the oceans.
Depending on the temperature, water can exist as a liquid, a gas (water
vapour) or a solid (ice). Although existing in all three phases, the total volume
of water in the atmosphere, on the land, and in the oceans remains essentially
constant over time. However, waters of the oceans, atmosphere, and lands
move in a great and continuous cycle known as the hydrologic cycle (see
Fig. 1.1).
Evaporation from the oceans, which are the basic reservoirs of free water, is
approximately 419,000 km 3 /year, while evaporation from soil, plants and water
on the continents is only about 69,000 km 3 /year. The total quantity of the
evaporated water, 488,000 km 3 /year, must be returned annually to a liquid or
solid state through precipitation over the oceans and continents. Precipitation
over continents is about 37,000 km 3 /year larger than evaporation. This excess
of quantity flows over or under the ground to reach the sea. Because of the
cycling of water, freshwater is a 'renewable' resource in the sense that supplies
of freshwater are constantly renewed by rainfall over the land and ocean.
S. R. Massel, Fluid Mechanics for Marine Ecologists
© Springer-Verlag Berlin Heidelberg 1999