PHYSICAL PROPERTIES OF SEAWATER

How Unique is Water?

• Water is one of only 3 naturally occurring liquids (mercury and ammonia)

• Only substance occurring naturally that exists in all 3 states – solid, liquid, and gas – on Earth’s surface

• Extremely large liquid range (0oC - 100oC)• Expands, becomes less dense as a solid

The Nature of Pure Water

• Water made of 2 hydrogen atoms and 1 oxygen atom

• Water is a polar molecule (+ end & – end)• Water’s unusual structure causes them to

“stick together”• Water molecules form hydrogen bonds• Hydrogen bonds not very strong, but make

water different from any other substance on Earth

Figure 3.1

Water has…

• Cohesion – sticks to itself

• Adhesion – sticks to others

• Surface Tension – a measure of how difficult it is to stretch or break the surface of water– No waves without

surface tension

Water has…

• Low Viscosity – little resistance to flow• Good for Earth’s marine organisms –

WHY?

The Three States of Water

• Water is the only substance that naturally occurs as a solid, liquid and gas on Earth

• Evaporation absorbs heat• Condensation releases heat

Water is Weird

• Density – the mass of a certain volume of a substance

• Solid water is less dense than liquid water• Water becomes more dense as it cools

– Water is most dense @ 4º C– Becomes less dense as it nears 0º C

• Good for the planet – WHY?

Heat Capacity

• The amount of heat required to raise the temperature of 1 gram of a substance 1º C– Water has one of the highest– 1 calorie raises 1 gram of water 1º C– It absorbs large amounts of energy before the

temperature changes• Good for earth’s climate – WHY?

Changes of State

• Latent Heat of Fusion / Melting –– The amount of heat required to melt a

substance without change in temperature– 80 calories per gram

Changes of State

• Latent Heat of Vaporization / Condensation–– The amount of heat required to change a

substance from a liquid to a gas without change in temperature

– 540 calories per gram

Why is Water Important?

• Water is the universal solvent• Water can dissolve more than any

other natural substance• Water can dissolve many hydrophilic

substances – Ionic compounds– Other polar compounds

• Form “spheres of hydration”• http://

programs.northlandcollege.edu/biology/Biology1111/animations/dissolve.html

Figure 3.5

Seawater has dissolved solids…

• Source –– Chemical weathering of crustal rocks– Hydrothermal vents– From volcanic eruptions

Water …• Density of pure water is 1 g/mL @ 4º C• Density of seawater is 1.0278g/mL @ 4ºC• Density is determined by temperature and

salinity– Seawater gets denser as it gets saltier, colder

or both• Because temperature varies more than

salinity, density is controlled by temperature

Density…• Changes with depth• Densest water sinks• Ocean becomes layered, stratified• Seen in profiles of salinity, temperature,

and density• The greater the difference in density

between surface and deep water, the more stable the water column and the harder it is to mix vertically

Figure 3.31

Pressure…• Water is noncompressible – does not

change volume with increasing pressure• So is seawater• Pressure increases with increasing depth

– Has small effect on volume– 1 atm (14.7 lbs/in2) for every 10 m (33 ft)– Pressure in deepest trench ~1100 atm– As pressure increases, gases are

compressed

Figure 3.13

Buoyancy• The ability of an object to float by

displacing a volume of water equal to its own weight

Water…• Transmits energy

– Heat– Light– Sound

• Refraction – the bending of light and sound waves due to density differences that affect the speed of energy transmission– increases with increasing salt, decreases with

increasing temperature

Water…• Transmits heat energy by

– Conduction – molecule to molecule– Convection – moving fluids & density driven– Radiation – direct from source (sun)

Water is …• Transparent –

transmits light energy readily– Important for

photosynthesis– Oceans are blue

because blue light penetrates the deepest

– Coastal waters sometimes green because blue absorbed

Water…• Transmits sound faster & farther than in air

– 1500 m/s in seawater (& 60 times farther)– 334 m/s in air

• At 1000 m combination of salinity, temp & pressure creates a zone of minimum velocity for sound – the Sofar Layer (sound fixing and ranging layer)– Sound waves produced here do not escape

& travel long distances

Sofar Channel