Chemical Composition of Seawater
70% of earth’s
surface is covered in
water – let’s see
what’s in that water!
What is actually in seawater?
Every naturally occurring
element on earth has
been found in seawater.
Obviously, seawater is
The rest of seawater is
composed of the
Seawater is Consistent
Law of Constant Proportions:
The ions in the world’s oceans remain relatively constant.
In other words…
In almost all of the world’s oceans the ratios of each ion to one another
remain the same:
55% chloride:31% sodium:8%sulfate:4%magnesium:1%calcuim:1%potassium
Q: Can you think of a place that might be the exception to this rule?
A: Where rivers meet the sea…river water frequently contains more
How did the salt get to the sea?
Salt is added to ocean water by…
• Weathering: On land, rivers carry eroded rock
and mineral debris containing salts out to the
• Seismic Activity: In the deep sea, underwater
volcanoes & vents react with seawater and
spew lava, rock, and/or mineral debris
containing salts into the sea around them
Salt is removed from ocean water by…
• Sea Spray: We will see evidence of this at Sunken
Forest in the spring. Have you seen it on your
sunglasses after a day at the beach? (remember
• Sediment Deposits: as sediment falls to the
seafloor, sometimes it binds to minerals in the
water around it or just gets buried
• Biological Activity: through the processes
associated with life, marine animals and plants
sometimes take in salts from the water around
Q: Why aren’t the oceans getting
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