Ocean Water Chemistry
Chap 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
35 grams
of
dissolved
salts
ocean water
35 parts
per
thousand
965
grams of
water
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 Sea
The 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?
• HYDROMETER
A tube that is
calibrated and is
put in the water to
see how high it
floats!
Other Ocean Properties
• Temperature:
Warm water = lower density;
rises
Cold water = higher density;
sinks
As 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 scarce
Amount of dissolved oxygen is
affected by temperature!
Higher temp = less oxygen
Lower temp = more oxygen
Temperature variation in oceans
EQUATOR
WARMER temps near
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.