How Ocean Water Differs from Fresh Water 10.2

Objectives List the ways salt water differs from fresh water Describe what salinity is and how it affects ocean waters Describe the characteristics between ocean water and fresh water in terms of density, freezing point and boiling point The role of both fresh and ocean water

Salinity If the oceans are constantly being filled up with fresh water, as the water cycle shows, why is ocean water not clear and fresh? The amount of salt dissolved in water is called salinity

Salinity Ocean water’s salinity = 200X greater than fresh water Average salinity of oceans is 35 parts per thousand Oceans at equator (evaporation) and poles (ice) have the highest salinity (removing water increases salinity) Ocean locations near rivers have low salinity, due to addition of fresh water

Composition of Water Salt water is composed of minerals dissolved during run-offs occurring over millions of years Volcanic eruptions also release minerals from inside Earth Sodium ions (Na+) and chloride ions (Cl-) are most common solids in ocean water Na+ ions and Cl- ions > 75% of all solids in ocean water Mixed and joined in the ocean, NaCl is chemical name for salt

Composition of Water Near the continents freshwater from rivers empties into the oceans since the river waters are fresh water (little salt), it dilutes the ocean water near the continents

Where Does the Salt Come From? Land Rain falls on the land and makes it way to streams and rivers When water travels through the ground , it picks up materials (such as salt). We call these materials dissolved solids. Eventually these materials get into the oceans In the oceans, the dissolved solids are well mixed because the water is moving constantly

Dissolved solids are in the ground Dissolved solids are in the ground. As the water seeps from the ground into streams and rivers, it carries the solids with it. Eventually they end up in the oceans.

Density of Salt Water Density = how tightly packed the molecules are in an object Less dense always floats on more dense Eg. warm air rises above cool air, and oil floats on water We float better in salt water than fresh water

Where Does the Salt Come From? Volcanoes Undersea volcanoes spew materials into the water On land, volcanoes spew materials into the atmosphere (these materials condense in clouds and are returned to the oceans when it rains) Under water volcano African volcano

Lava going into the ocean at Hawaii’s Volcanoes National Park

Freezing Point of Salt Water Salt water has slightly different properties than fresh water Salt water freezes at –1.9 ºC

Freezing Point of Salt Water This is why we add salt to the gravel when the trucks sand the roads in the winter time The salt lowers the temperature of freezing causing the ice to melt!