-
8/6/2019 Bonne Bay Presentation #1 Salinity and Chemical Comp of
Seawater
1/15
Salinity in the Worlds Oceans and
the Chemical Composition ofWater
1
Garry & Shannon
-
8/6/2019 Bonne Bay Presentation #1 Salinity and Chemical Comp of
Seawater
2/15
Salinity is defined as the total quantity of
dissolved salt in seawater measured in PSU.
Measured in grams per kilogram (g/kg)
The average salinity of seawater is 33-37ppt
Six ions make up more than 99% of the salts
dissolved in seawater: sodium (Na+),
magnesium (Mg+
), calcium (Ca2+
), Potassium(K+), chloride (Cl-), and sulfate (SO4
2-)
When saltwater and freshwater meet an
estuary is formed.
Salinity and Chemical Composition of
Water
2
-
8/6/2019 Bonne Bay Presentation #1 Salinity and Chemical Comp of
Seawater
3/15
3
Chemical composition of seawater
-
8/6/2019 Bonne Bay Presentation #1 Salinity and Chemical Comp of
Seawater
4/15
4
Salinity in the worlds bodies of water
-
8/6/2019 Bonne Bay Presentation #1 Salinity and Chemical Comp of
Seawater
5/15
5
Latitude versus salinity
-
8/6/2019 Bonne Bay Presentation #1 Salinity and Chemical Comp of
Seawater
6/15
6
The distribution of sea-surface salinity also tends to be
zonal.
The saltiest waters are at mid-latitudes where evaporation
is high. Less salty waters are near the equator where rain
freshens
the surface water, and at high latitudes where melted sea
ice freshens the surface waters.
The zonal (east-west) average of salinity shows a close
correlation between salinity and evaporation minusprecipitation
plus river input.
Salinity distribution
-
8/6/2019 Bonne Bay Presentation #1 Salinity and Chemical Comp of
Seawater
7/15
7
Mean sea-surface salinity
-
8/6/2019 Bonne Bay Presentation #1 Salinity and Chemical Comp of
Seawater
8/15
Factors that affect the chemical composition of the sea
1. Exchange with the atmosphere (eg, nitrogen cycle)
2. Solubility of different compounds
3. Reduction by anaerobic bacteria
4. Precipitation and exchange with the ocean bottom5. Inflow of
fresh water
6. Freezing and melting of sea ice
7. Chemical reactions that control or influence the
concentrations
of different elements
8. Hydrothermal discharges from deep sea vents
9. Biological processes eg, life processes and decomposition
8
-
8/6/2019 Bonne Bay Presentation #1 Salinity and Chemical Comp of
Seawater
9/15
9
The Effects of Adding Salt to Water
The specific heat (the amount of heat necessary to
raise the temperature of one gram of water one
degree) decreases with increasing salinityThe density increases
as salinity increases
Freezing point decreases when salinity increases
The vapour pressure is lowered as salinity
increases
Osmotic pressure increases as salinity increases
-
8/6/2019 Bonne Bay Presentation #1 Salinity and Chemical Comp of
Seawater
10/15
10
The density increases as salinity
increases
As salinity increases and the
temperature decreases the density
increasesFreshwater has the highest density at 4
degrees Celsius, Saltwater of ~ -1.8
degrees celsius with a ppt of 35.
-
8/6/2019 Bonne Bay Presentation #1 Salinity and Chemical Comp of
Seawater
11/15
-
8/6/2019 Bonne Bay Presentation #1 Salinity and Chemical Comp of
Seawater
12/15
12
Depth and salinity
-
8/6/2019 Bonne Bay Presentation #1 Salinity and Chemical Comp of
Seawater
13/15
13
Ways to measure salinity
Salinometer
Electrical conductivity (CTD can measure this)
Boiling of saltwater to measure the amount of salt left per
litre
of saltwater
Chemical method using ion ratios (possible due to
commonratios)
-
8/6/2019 Bonne Bay Presentation #1 Salinity and Chemical Comp of
Seawater
14/15
14
Local examples and information
Average salinity is 30 in
Labrador current due to
high precipitation versusevaporation ratio, highest
at deep-water upwelling
(~35)
-
8/6/2019 Bonne Bay Presentation #1 Salinity and Chemical Comp of
Seawater
15/15
15
