Ahhhhhh…. SEAWATER

Seawater

• Seawater is a solution of about 96.5 percent water and 3.5 percent dissolved salts.

Seawater

• The most abundant salt in seawater is sodium chloride (NaCl).

SeawaterSeawater

• Salinity is a measure of the amount of dissolved salts in seawater

• Parts Per Thousand (ppt).

• The total salt content of seawater is, on average, 35 ppt, or 3.5 %

Variations in Salinity• 37 ppt in subtropical region• Salinities are lower in equatorial regions where

precipitation is abundant. • Salinities of 32 or 33 ppt occur in polar regions• The lowest salinities often occur where large rivers

empty into the oceans.

Chemical Properties of Seawater

Seawater

Sources of Sea Salt Seawater

– Minerals flushed in by Rivers – Weathering of crustal rocks – Chlorine and sulfur dioxide dissolve in water from

Volcano Eruptions

Removal of Sea Salts Seawater

– Salts are removed and added at the same rate.

• Some sea salts precipitate from seawater near arid, coastal regions.

• Salty spray droplets from breaking waves are picked up by winds and deposited inland.

• Marine organisms remove ions from seawater to build their shells, bones, and teeth.

Chemical Properties of Seawater

• Freshwater has a maximum density of 1.00 g/cm3 - density of seawater 1.02 g/cm3 -1.03 g/cm3

Seawater

_ Cold water (sinks) is more dense than warm water (rises)

• Freezing point: Sea= -2 C Fresh = 0 C

Absorption of Light Seawater

– Water absorbs light, which gives rise to another physical property of oceans—they are dark.

– In general, light penetrates only the upper 100 m of seawater.

Ocean Layering• Ocean surface temperatures range from

• –2°C in polar

• 30°C in equatorial

• average surface temperature being 15°C.

Seawater

• Ocean water temperatures decrease significantly with depth.

Ocean Layering• A typical ocean

temperature profile plots changing water temperatures with depth.

Seawater

Seawater1. The first layer is a relatively warm, sunlit, surface layer some 100 m thick.

2. The thermocline is a transitional layer which is characterized by rapidly decreasing temperatures with depth.

3. The bottom layer is cold and dark with temperatures near freezing.

Ocean Layering• Both the thermocline and the warm surface layer are

absent in polar seas, where water temperatures are cold from top to bottom.

Seawater

• In general, ocean layering is caused by caused by density differences of warm and cold density differences of warm and cold water. water.

• Cold water migrates toward the equator as a cold, deep water mass along the ocean floor.

Water Masses• Three water masses account for most of the deep

water in the Atlantic Ocean.

Seawater

1.Antarctic Bottom Water forms when antarctic seas freeze during the winter and water temperature drops below 0°C.

2.North Atlantic Deep Water forms in a similar manner offshore from Greenland.

3.Antarctic Intermediate Water forms when the relatively salty waters of the Antarctic Ocean decrease in temperature during winter and sink.

Water MassesSeawater

• The Indian and Pacific Oceans contain only the two deep antarctic water masses.

Section Assessment

1. By what processes are salts removed from seawater?

Seawater

Salts are removed from seawater through the formation of evaporites, sea spray that is carried inland by wind, and biological processes.

Section AssessmentSeawater

2. What is a thermocline?

A thermocline is a transitional layer between warm surface waters and cold bottom waters in a body of water that is characterized by rapidly declining temperatures with depth.

Section Assessment

3. Identify whether the following statements are true or false.

Seawater

______North Atlantic Deep Water overrides Antarctic Bottom Water.

______ Photosynthesis can occur to a depth of 200 m.

______ Sodium is the most prevalent ion in seawater.

______ Salt water is always denser than freshwater, regardless of temperature.

true

false

false

true