Salt Water Oceans 11

Properties of Salt Water Salinity is the amount of dissolved salts in water. 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 ppt. 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 crust.

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, no rivers drain out. The 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 point.

Salinity and Density Seawater is more dense than freshwater, so freshwater floats on seawater. An increase in salinity, increases the density. A HYDROMETER is an instrument used to measure the buoyancy of a liquid by comparing its buoyancy to that of pure water.

Hydrometer It can be used to measure density. If the liquid is more dense than water, the hydrometer will float higher. 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 salt. 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 behind.

Sources of Salts in the Ocean