Physical Oceanography

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Chapter 15

• Physical Oceanography
• Section 2 Seawater

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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.

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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

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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

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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.

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Major Ions in Seawater
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Variations in Salinity

• High salinity- areas with high rates of
  evaporation.
• Low salinity areas where rivers empty into
  oceans.

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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!

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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

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Remember the water cycle?
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Physical Properties of Seawater

• Density - Salt ions are heavier than water
  molecules
• Temperature
• Salinity
• Absorption of Light

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Seawater vs. Freshwater

• SEAWATER
• 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
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Absorption of Light

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

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

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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

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End of Section 2