Ocean Water Chemistry Chap 14, Sec 4

Essential Questions: How salty is ocean water? Why is the ocean salty? Why doesn’t the salinity change drastically? How do the temperature and gas content of ocean water vary? How do conditions in the ocean change with depth?

What is Ocean water made of? Dissolved gases Such as oxygen, carbon dioxide, and nitrogen Dissolved salts Such as chloride, sodium, sulfate, magnesium, calcium, and potassium Calcium, magnesium, and sodium come from rocks and are dissolved slowly by rivers and groundwater Sulfate and chloride come from erupting volcanoes

Salts in Seawater Sodium and chloride make up 85 % of ions in saltwater. When removed from water these combine to make halite (common table salt). Salinity is the measure of the amount of salts dissolved in seawater. One kilogram of seawater contains about 35 g of dissolved salts (3.5 %) This means……If you boiled a kilogram of ocean water in a pot until all the water was gone, there would be about 35 grams of salt left in the pot.

Differences in Salinity Warm ocean water has higher salinity than cold ocean water because the water often evaporates and leaves salts behind. Pure ocean water has higher salinity than water that has mixed with fresh water – such as where a river empties into the ocean. Surface water is lower in salts than deeper water because of rain, freshwater mixing in, melting ice and such. Water near the poles is saltier than other places because the salt doesn’t freeze with the water – which leaves more salt there.

Steady State of the Oceans The oceans are in balance because the salinity has remained constant for hundreds of millions of years. Scientists have gathered evidence that says the oceans are not growing saltier. Rivers, volcanoes, and the atmosphere constantly add material to the oceans. Organisms use dissolved salts to make shells, marine animals remove calcium ions from the water to form bones, other animals use the dissolved calcium to form shells. Elements are added to the ocean at about the same rate as they are removed.

Salinity affects the properties of water. Ocean water freezes at a lower temperature than fresh water (at 28.58° instead of 32° ) Ocean water is denser than fresh water. As a result, Salt water weighs more than fresh water you can float more easily in ocean water than in fresh water (buoyancy increases) Look at the picture on page 374!

Other Ocean Properties Surface temperatures of the ocean vary (just like on land) with location & seasons Gases in ocean water vary as well.

Ocean Surface Temperature The ocean absorbs energy from the sun. Near the equator, the temperature at the surface of the ocean is about 25°C— ( 77° F) about room temperature. The temperature drops as you go away from the equator.

Gases in the Ocean Vary: Ocean organisms use gases in ocean water. Two gases that ocean organisms use are carbon dioxide and oxygen. Algae, for example, need carbon dioxide to carry out photosynthesis. Ocean animals need oxygen. There is much more carbon dioxide in the ocean than in the air. There is much less oxygen in the ocean than in the air. Surface water has more oxygen in it than deeper water has.

Changes With Depth As you descend through the ocean, the water temperature decreases. The deeper you go in the ocean, the colder and denser the water is. Cold water is denser than warm water (which means it rises). Pressure increases continuously with depth in the ocean.

Changes with Depth Temperature decreases as depth increases. - Ocean Water Chemistry Changes with Depth Temperature decreases as depth increases. Pressure increases as depth increases. Light decreases as depth increases.

Water Pressure If you could drop from the ocean’s surface to the ocean floor, you would pass through a section of the ocean known as the water column. Conditions change as you go from the top of the water column to the bottom. There are three temperature zones in the water column. The surface zone is warmest. The transition zone begins at about 1 kilometer (.6 miles) down. Temperatures drop quickly in the transition zone. Below the transition zone is the deep zone, where the water is very cold. Water pressure is the force of the weight of water. Because of high pressure in the deep ocean, divers can go down safely to only about 40 meters (131 feet).

Essential Questions - Answered: How salty is ocean water? 3.5% - 1 kilogram of ocean water contains 35 grams of salts Why is the ocean salty? The ocean is salty because salts are dissolved from rock by water flowing to the oceans. Why doesn’t the salinity change drastically? The oceans are balanced. About as much salt is added as is removed.

Answers Continued How do the temperature and gas content of ocean water vary? Temperature varies based on latitude and seasons. Gas content varies based on temperature – cold water contains more oxygen while warm water contains more carbon dioxide. How do conditions in the ocean change with depth? As depth increases, temperature decreases, light decreases, and the pressure increases.