Why is the Sea Salty

Salt Water
Oceans 11
Properties of Salt Water
 Salinity
is the amount of dissolved salts in
 The salinity of the ocean averages 35 ppt
(parts per thousand).
 Fresh water averages 10 ppt.
 There are some variations in salinity due
to differences in: the rates of evaporation,
precipitation, and run-off.
Differences in Salinity
 The
salinity of the Red Sea is 41ppt and
the salinity of the Dead Sea is nearly 300
 Table salt (NaCl) accounts for 87% of the
salinity of sea water.
 Sea water contains at least a trace amount
of most elements found in the Earth’s
Red Sea
Dead Sea
Why is the Dead Sea so salty?
 Continually
fed water from the
rivers and streams coming
down off the mountains that
surround it.
 BUT,
 The
no rivers drain out.
only way water gets out is
through evaporation which
leaves behind all of the
dissolved minerals.
Salinity and Freezing
 Salinity
affects the freezing point of water.
 When ice forms in seawater the salt is
extruded from the ice, leaving a more salty
water beneath the ice.
 Seawater therefore has no fixed freezing
Salinity and Density
Seawater is more dense
than freshwater, so
freshwater floats on
An increase in salinity,
increases the density.
instrument used to
measure the buoyancy of
a liquid by comparing its
buoyancy to that of pure
 It
can be used to measure
 If the liquid is more dense
than water, the
hydrometer will float
 If the liquid is less dense
than water, the
hydrometer will sink more.
How salty is the ocean?
Maybe 50 million billion tons of dissolved solids.
If the salt was removed, it would cover the
Earth’s surface, 500ft thick.
When 1 cubic foot of ocean water evaporates, it
leaves 2.2 pounds of salt.
When 1 cubic foot of Lake Michigan (fresh
water) is evaporated, it leaves 0.01 pounds of
So, sea water is 200x saltier than fresh water.
Caused by salt entering the ocean from run off
from the land.
Salt enters the sea
from rivers and
streams, and then is
deposited on the
ocean floor.
The Sun’s heat
vaporized pure water
and leaves the salt
Sources of Salts in the Ocean