Ocean Water ChemistryChap 13 – Section 3

Why is ocean water salty?

•Undersea volcanoes erupted, ejecting chemicals into the water

•Rains eroded land washing chemicals from rocks into the ocean

•Over a LONG period of time this produced the salty ocean water

SALINITY•Salinity is a measurement of the total

amount of dissolved salts in a sample of water

•Average % - ocean water is 3.5% dissolved salts and 96.5% water

•Salinity usually measured in parts per thousand

1000 g sample of ocean water

35 grams of

dissolved salts

965 grams of water

35 parts per

thousand

Composition of Seawater•Sodium chloride is

present in the largest amount

•In water, it dissolves and the sodium and chloride separate into ions.

•Sodium & Chloride ions make up over 80% of the ions in salt water!

Variations in salinity

•Salinity is usually lower at the surface. WHY?

Rain, sleet, etc adds fresh water lowering the salinity.

Salinity is usually lower near the mouths of rivers. WHY?

Rivers dump fresh water into the ocean!

Salinity is usually higher near the equator and the poles. WHY?

Surface water evaporates in the warming climates leaving salt behind or surface water freezes leaving salt in liquid water.

How does salinity levels affect the water?

•It lowers the freezing point of water. Ocean water freezes at -1.9oC instead of 0oC.

•Salt water has a higher density than fresh water therefore saltwater has a greater buoyancy.

•It “lifts” floating objects higher.

The Dead SeaThe Dead Sea is the saltiest body of water in the world – it has the highest salinity.It has a salinity 8.6 times ocean water’s salinity.Salinity is btw 300 – 400 parts per thousand!!

Click for video!

What is used to measure salinity?•HYDROMETERA tube that is

calibrated and is put in the water to see how high it floats!

Other Ocean Properties• Temperature:Warm water = lower

density; risesCold water = higher

density; sinksAs you move away from

equator ocean water temp decreases.

Temperature decreases with depth.

Deeper = colder!

•Gases:Dissolved gases in water

that organisms must have to live!

Oxygen and Carbon Dioxide

CO2 is very plentiful in the ocean.

O2 is more scarceAmount of dissolved

oxygen is affected by temperature!

Higher temp = less oxygenLower temp = more

oxygen

Temperature variation in oceans

WARMER temps near equator!

EQUATOR

•Comparison of Salinities

•Brine has the highest

•Fresh has the lowest

•What does ppt stand for?

CHANGES WITH DEPTH•Temperature decreases and pressure

increases!

In order for scientists to study under water they must use SUBMERSIBLES. They are built to resist pressure.

Lab –Investigating Changes in Density

•We are going to make our own hydrometer using a pencil and tacks!

•You are going to measure the differences in density of warm and cold water.

•You will then measure water samples with different salinities.

•Read the lab on pg. 454 of your textbook.