Sea Water Properties

Sea Water Properties

Sea Water Properties

Properties of sea water:

  1. Salinity – why is it salty?
  2. What kind of salt is it?
  3. Density of sea water & it’s effect

Important vocabulary

•Salinity = Saltiness

•Salinity = how much salt is in the water

•Salt = another name for IONIC COMPOUND

NaCl MgCl2 CuSO4 - all “salts”

What is the salinity of the oceans?”

on average it is ~33ppt (parts per thousands)


Or, - each kg of ocean water has 33 grams of salt in it.

Fresh water –

Brackish water –

Salt water –

Brine –

River water dissolves “salts” from the land and carries them to the ocean

Rivers are about 0.1ppt salinity

•Bicarbonate HCO31-58.4%



•Chloride Cl1-7.8%

  • SodiumNa1+6.3%

Salinity: Why is the ocean salty?

If you had a glass, and you put slightly muddy water in it, then let it all evaporate… then refilled it with more muddy water, and let it evaporate, …. What would happen?

If you had another glass and you put tap water in it, (is tap water pure?) and let it evaporate, then refilled, and let it evaporate, and you did this 10000 times…. What would happen?

So why is the ocean salty?

•All the dissolved stuff from rivers accumulated over time.

•But…. If you look at the ocean there has to be more to it!

What type of salt is it?
Composition of sea salt compared to rivers – NOT just concentrated rivers salts


•0.1 pptvs.32 ppt

Bicarbonate58.4%Chloride 55%

Calcium15%Sodium 30.6%

Sulfate11.2% Sulfate 7.68%

Chloride7.8% Magn. 3.69%

Sodium6.3% Calcium 1.16%

Potassium 1.10%

So, why is the ocean’s salt different than just “concentrated river” salt

•Things use the calcium & carbonate to make shells of calcium carbonate

•Also, Many algae, (Diatoms) make their shells from Silica (glass/sand).

•Short answer: Some of the dissolved stuff is useful, and so is taken out.

Sea Water’s Density

-Which is denser Salt water or fresh water?

-Which is denser cold water or hot water?

-So what are the two things that can change water’s density?

-How does temperature and salinity affect ocean water?

So when a river flows out, does it flow on top or to the bottom of the ocean?

2nd place density takes a big effect

1st – is estuaries (rivers meet ocean)

fresh water vs salt water

2nd – is the cold north and south poles

salt water vs cold saltier water

Evaporating and freezing “purifies” water.

What color is water and ice?

What happens to salt and other stuff when water freezes? Does it stay or get pushed out?

Freezing ocean creates saltier cold water… that sinks!

Water sinks at the poles – due to increased density


  1. Oceans are salty due to river imput of thousands of years of dissolved minerals
  2. Ocean salt is not the same as river salt because of biology (uses some of the salts)
  3. Density of sea water is controlled by salt and temperature

Sea water tends to sink at the poles due to increased salinity and decrease in temperature.