OCEANOGRAPHY

Physical and Chemical

Properties

Outline

• 1. Chemical Make-Up of Water• 2. Heat Capacity of Water• 3. Salinity of Water• 4. Density of Water• 5. Viscosity• 6. Surface Tension• 7. Pressure• 8. Transmission of Light in Water• 9. Transmission of Sound in Water• 10. Thermal Layers in Water• 11. Dissolved gases

1. Chemical Make-Up of Water

• H2O – 2 hydrogen joined together with

1 oxygen

1. Chemical Make-Up of Water

• Water molecules are dipolar with a + charge on the hydrogen side and a – charge on the oxygen side.

Chemical Make-Up continued

• Hydrogen and Oxygen share electrons forming a strong covalent bond. It is hard to break the hydrogen and oxygen molecules apart.

• There are also weak hydrogen bonds between one water molecule and another. These bonds are more easily broken.

Properties of WaterVideo

Heat Capacity

• Water has the ability to absorb or give off heat without experiencing a large temperature change.

• Water changes temperature at 1 degree per gram per calorie in the liquid state.

Heat Capacity

• Note: Organisms living in sea water experience less seasonal temperature fluctuation than those living in air, sand, or wood. At 1,000 m the ocean is the most thermally stable environment on earth with an average temperature of 3.5 degrees Celsius.

SALINITY

• Salinity – is the total amount of dissolved ions in water.

• It is measured in parts per thousand (ppt) 0/00.

• Salts such as NaCl (sodium Chloride) split apart and are attracted to the charged poles of the water molecule.

• Na(+) is attracted to oxygen side(-), • Cl(-) is attracted to hydrogen side(+)

SALINITY

• Seawater is:– 96.5% or 965 ppt pure water– 3.5% or 35 ppt dissolved ions– Many of these dissolved ions are inorganic

salts from weathered rocks.

SALINITY

Salinity is altered by processes that add or remove salts from the sea.1. Evaporation – salinity increases2. Precipitation – salinity decreases3. River runoff – salinity decreases4. Freezing of sea ice – increases the salinity of surrounding water5. Thawing of sea ice – decreases the salinity of surrounding seawater

SALINITY

• Salinity and the Water Environment– Freshwater - 0 – 6 ppt – Brackish - 7 – 22 ppt– Seawater - 23 – 40 ppt

OTHER SUBSTANCES DISSOLVED IN WATER

• 1. Dissolved gases – O2, CO2

• 2. Organic compounds from living organisms– Wastes products, fats, oils, amino acids

3. Pollutants

DENSITY

• Density=mass/volume• Temperature and Density• Water above 40C decreases in density as

temperature increases

• Water increases in density as it’s temperature decreases until it reaches 40C

• Water is most dense at 40C, then decreases in density until it freezes

DENSITY

• Water Density and Salinity

• Water density is affected by the salts dissolved in it. The more salt it contains, the denser it becomes.

• The density of fresh water at 40C is 1.000g/ml

• The density of seawater at 40C is 1.028g/ml

DENSITY

• Water of low density floats

• Water of high density sinks

• Cooler water with high salinity is more dense and will therefore cause surface water to sink

SALINITY, DENSITY, TEMPERATURE GRAPH

•

VISCOSITY

• Viscosity is the tendency of water to resist external forces that would separate its molecules (cohesion)

• Viscosity reduces the sinking tendency of some objects and organisms which could allow them to sink or float slowly.

• Viscosity slows down swimming due to frictional drag.

VISCOSITY

• COLD water has a greater viscosity than Hot water.

• Greater salinity results in greater viscosity.

SURFACE TENSION

• The mutual attraction of water molecules creates a flexible molecular skin over the water surface.

• Note: Both viscosity and surface tension are temperature –dependent increasing with decreasing temperature.– Seawater at 00C is 25%more viscous than

seawater at 200C

PRESSURE

• Hydrostatic Pressure - is due to the weight water pressing on submerged objects.

• Pressure = force/surface area• 1atm = 14.7 pounds per square inch• As an object descends to a greater depth the

pressure from the atmosphere and the water pushes on it.

• Every 10 meters of depth exerts an additional 1 atmosphere of pressure on an object.

PRESSURE

• 1 atm (atmosphere) of pressure from the air surrounding the earth is pushing on the oceans, lakes, rivers and ponds.

• For each additional 10 meters of depth there is 1 more atmosphere of pressure.

Depth (m) Pressure (atm)

0 (surface) 1

10 2

20 3

60 7

PRESSURE

• Marine and freshwater organisms bodies change to equal the pressure of the water as they swim to different depths.

• Some BENTHIC ORGANISMS are subjected to a pressure of 340 atm.

• SPERM WHALES – dive from the surface to a depth of 2,250 m and return in 1 hour.

PRESSURE

• Affects of Hydrostatic Pressure on Life Functions

• Gases become more soluble at high pressures.

• Gas filled spaces in an organism may expand or contract with changes in depth.

• Some enzymes are inactivated.• Metabolic Rates for a given temperature

tend to be slightly higher.

Pressure on diver

• Pressure on diver +1,248 psi

PRESSURE

Depth

(m)

Water Pressure (atm)

Volume of air in lungs (atm)

0 1 5.0

10

40

Light in Water

• Transparency – seawater is relatively transparent allowing photosynthesis to proceed at some distance below the surface.

• Water is more transparent to some colors than others. In clear water, blue light penetrates deepest making deep clear ocean water appear blue. Red is absorbed at the surface.

Light in Water

• 70% of the photosynthesis in the world takes place in the uppermost layer of the ocean.

• Some light is reflected off the surface.• Light penetrating the surface is refracted (bends)

because light travels faster in air than in water. The speed of light in water is 3/4 of its speed in air. Refraction increases with greater salinity.

• Greater abundances of solids (dust, salts, bits of body tissue) in the water decrease the depth of light penetration.

Transmission of Light

Transmission of Light in Water

Refraction

SOUND IN THE SEA

• Sound can travel much greater distances through water than light before being absorbed.

• Because sound travels so efficiently through water, many animals use sound rather than light to see. (ex. Sperm Whale)

• The speed of sound in water is about 3,345 miles per hour but fluctuates with depth.

SOUND IN WATER

• Sound waves refract (bend) toward layers of lower sound velocity.

• Sound waves made in the minimum velocity layer (SOFAR – SOund Fixing And Ranging layer)

• Sound in the SOFAR layer can travel for thousands of kilometers.

THERMAL LAYERS

• Water is warmer near the surface.

• Then as one descends the temperature of the water gets cooler

• There is a layer of rapid temperature just below the photic zone. This area is called the themocline.

• In the deepest water even at the equator, the water temperature is around 40C.

GASES IN WATER

• Water contains dissolved nitrogen, oxygen, carbon dioxide, and other gases.

• Cold water can hold more dissolved gas, (ex. oxygen) than warm water.

• Fresh water can hold more dissolved gas than seawater.

GASES IN WATER

• Which body of water holds the most dissolved oxygen?

• 410F freshwater

• 410F seawater

• 740F freshwater

• 740F seawater