Physical OceanographySection 2: Seawater

Chapter 15.2 - ObjectivesI 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: elementschlorides & sulfates of magnesiumPotassiumCalcium

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 compositionSalt Ions (ion is an atom that gains or loses an

electron)Dissolved gases (oxygen, nitrogen, carbon dioxideDissolved nutrients (nitrates, phosphates,

silicates)

These nutrients and gases greatly affect life in the oceans.

Major Ions in Seawater

Variations in SalinityHigh 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

TemperatureSalinityAbsorption of Light

Seawater vs. Freshwater

SEAWATER:

More denserDensity 1.02 g/cm3 to 1.03 g/cm3

This density affects oceanic processesFreezing point -20C

FRESHWATER:

Less denserMax density 1.oo g/cm3

Freezing point 00C

Calculation: d= m/V

Absorption of LightWater absorbs light

Light penetrates only upper 100m of seawater

Below is darknessPhotosynthesis 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 Masses1.Antarctic Bottom Water – forms when sea freezes – below 00C

2.North Atlantic Deep Water –forms off the shore of Greenland

3.Antarctic Intermediate Water -least dense