The Salty Seas
Walking along a beach,
it is hard not to notice salt in the air, on your skin and on rocks washed
by ocean waves. When we were children we all had to try tasting sea water
at least once. We all decided it was not a fun beverage! We also may have
wondered just where all that salt comes from. It might surprise you to
know that all that salt likely originated in a place where people never
even see the ocean.
If you've ever dissolved a spoonful of salt in a glass of water, then you know part of the answer already -- salt dissolves very easily in water. As rain washes Earth's continents, the chemicals that form salts are dissolved out of rocks and carried by rivers and streams into the sea.
Salt can also be deposited by the sea onto land. This happens when sea level is high, in low-lying parts of a continent. At times, shallow seas cover some parts of a continent. When the level of the sea drops again, salt can be left behind.
But most of the salt goes the other way -- from land to sea. Streams and rivers make a great "highway" for carrying sediments to the sea. That fact has some larger implications. It's been said that all things flow to the sea. If you empty a car's radiator onto the supermarket parking lot at night when nobody's looking, that Ethylene Glycol will be washed by rain into storm drains, into streams and rivers, and ultimately into the sea. The sea is a sink for substances that come from land. These substances can be natural, like salt on rocks - or human made, serious pollutants.
Just as salt is deposited into the oceans, it would follow that in the polar regions, the ice formed from sea water would also be salty. Yet arctic explorers and natives know that sea ice that's at least several years old can be melted and used for drinking water. How can this be? Where does the salt go?
There are several ways in which the salt is expelled from sea ice. First, most of sea water's salt is rejected as the ice forms. As the water freezes the salt remains in the ocean water. Sea water has a typical salinity of 34 to 35 parts per thousand and that's pretty salty, we could never drink that! But sea ice has a salinity of only about 5 parts per thousand. .
Salt that's rejected during the freezing process accumulates in brine pockets within the ice. The brine, or salty water, gradually drains due to gravity. How quickly it drains depends on various conditions, including the temperature outside -- and the strength of a seasonal cycle by which Arctic ice melts and then re-freezes. The more the ice melts and refreezes, the less salty it becomes. Thus: the older the ice the less salty. Boiling the water will get rid of any bacteria and the water becomes safe and nearly salt free.
Copyright © 2001 Kathy A. Miles and Charles F. Peters II