Characteristics of Ocean
Water
13.1
Salinity, Temperature & Density
Relationships
How did the oceans form?
• About 4 billion years ago Earth began to
cool off.
• Cooling allowed water vapor to condense.
• Rain fell & filled in the deep spots on
earth.
• Presto…you’ve got an ocean!
But why is ocean water salty?
FACT:
• NaCl is the main salt in the ocean.
• So…where does the salt come from?
– Sodium = dissolved from rocks
– Chlorine = gas added from volcanic eruptions
How is the salt measured?
• Salinity is defined as the “total amount of
dissolved material” in the water
• Measured in parts per thousand ‰
• Typical measurement 33 – 37 ‰
Is it the same saltiness
everywhere?
• No! Evaporation and precipitation affect
how much salt an area contains.
• So…hot & dry coastal areas are saltier
(higher salinity = 38‰).
• Why? There is more evaporation and little
freshwater running into the oceans here.
Where is it less salty?
• Cool climates and more humid areas will
have a lower salinity (32‰).
• These areas have more freshwater that
runs into the ocean and dilutes the
seawater.
Movement affects salinity.
• Slower moving waters can become saltier,
since there is less mixing.
• An example is the Mediterranean Sea.
• Mixing decreases salinity.
Temperature & Oceans
• Ocean surface temperatures are usually
about 30°C at the equator.
• Ocean surface temperatures are about
2°C at the poles.
Temperature zones
• There are three temp. zones in the ocean:
– Surface zone 0 – 300 m deep
• Sunlight heats the top
• Surface currents mix this layer
– Thermocline 300 – 700 m deep
• Temps drop very fast here
– Deep zone 700 m to bottom
• Temps are usually 1°C to 3°C …brrrrr!
Florida International University Website:
http://www.coexploration.org/bermuda/html/thermocline_graph.html
Density
• Mass/unit volume
• Pure water is 1g/cm3
• Salt makes the water heavier (more
dense)
• Ocean water is 1.026 g/cm3
• Freshwater floats on saltwater!
• Evaporate 1 ft3 of seawater and you have
2.2 pounds of salt leftover!
Think about the Pamlico Sound
• Where is the salt water?
• Does the salt water ever reach New Bern?
• What happens when less water flows
downstream?
• What happens when more water flows
downstream?
Density…it makes a difference!
• Higher salinity = higher density
• Colder temps = higher density
• So the most dense water would be cold
with high salinity.
• The lowest density water would be warm
with low salinity.
Seasonal Changes in Ocean
Temps
• Why do we have to wear wetsuits to surf in
NC during the winter?
• Because the water is colder!
• Why?
• Because we receive less direct sunlight
during the winter.
• We receive more direct rays during the
summer, so the water is warmer then.