Physical Oceanography Section 2: Seawater Chapter 15 Physical Oceanography Section 2: Seawater

Chapter 15.2 - Objectives I will: Compare and contrast the physical and chemical properties of seawater. Explain ocean layering. Describe the formation of deep water masses.

Seawater is a solution Solution is a homogeneous mixture 96.5% water 3.5% dissolved salts. Most abundant salt is (NaCl) Other salts: elements chlorides & sulfates of magnesium Potassium Calcium

Salinity Measure of the amount of dissolved salts in seawater. Expressed in grams of salt per kilogram of water or parts per thousand (ppt) Total salt in seawater: avg 35 ppt or 3.5%

Seawater composition Salt Ions (ion is an atom that gains or loses an electron) Dissolved gases (oxygen, nitrogen, carbon dioxide Dissolved nutrients (nitrates, phosphates, silicates) These nutrients and gases greatly affect life in the oceans.

Major Ions in Seawater

Variations in Salinity High salinity- areas with high rates of evaporation. Low salinity – areas where rivers empty into oceans.

Sources of Sea Salt Salinity of ancient seas not much different than today. Magnesium in calcium-carbonate shells of marine organisms. Volcanoes- water vapor, gases (chlorine and sulfur dioxide) Weathering of Feldspar - Na, Ca, K Weathering of mineral and rocks - Fe, Mg These ions are flushed into rivers and transported in the oceans!

Removal of Sea Salts Salinity does not increase although salt ions continuously are added to seawater. WHY? Salts are removed at same rate as added Process to remove salts: Precipitate – forms deposits Marine Organisms- to build their shells, bones, teeth. Organism die – solid parts drift to the ocean floor

Remember the water cycle?

Physical Properties of Seawater Density - Salt ions are heavier than water molecules Temperature Salinity Absorption of Light

Seawater vs. Freshwater More denser Density 1.02 g/cm3 to 1.03 g/cm3 This density affects oceanic processes Freezing point -20C FRESHWATER: Less denser Max density 1.oo g/cm3 Freezing point 00C Calculation: d= m/V

Absorption of Light Water absorbs light Light penetrates only upper 100m of seawater Below is darkness Photosynthesis exists top 100m

Ocean Layers – caused by density differences Warm, sunlit Rapid temp. decrease Cold, dark, freezing temps.

Where does all the cold water come from? Polar seas Cold temp. causes seawater to become more dense Seawater freezes, sea ice forms Salt ions form beneath the ice Saltwater sinks, it migrates toward equator as cold, deep water mass

Deep Water Masses Antarctic Bottom Water – forms when sea freezes – below 00C North Atlantic Deep Water –forms off the shore of Greenland Antarctic Intermediate Water -least dense

End of Section 2