Download 13.3 Ocean Water Chemistry

Section 3: Ocean Water Chemistry
1. The Salty Ocean
a. Undersea volcanoes erupted, spewing chemicals into the water, building up
areas of land
i. Rain fell on the land, washing more chemicals from the rocks into the ocean
b. Salinity: the total amount of dissolved salts in a sample of water
i. On average, one kilogram of ocean water contains about 35 grams of salts—
35 parts per thousand
ii. Sodium chloride, table salt, is the most common salt in ocean water—86%
1. When dissolved, it separates into sodium and chloride ions
iii.Other ions include magnesium, calcium, sulfate, and potassium
c. Variations in Salinity
i. Near the ocean’s surface, precipitation adds fresh water, lowering the
salinity
ii. Salinity is also lower near the mouths of large rivers such as the Amazon
and Mississippi
iii.Evaporation increases salinity
iv.Salinity can also be higher near the poles
1. When water freezes into ice, the salt is left behind in the water
d. Effects of Salinity
i. Ocean water does not freeze until the temperature drops to about -1.9°C
1. Salt acts as a kind of antifreeze by interfering with the formation of ice
crystals
ii. Salt water is more dense than fresh water
iii.Seawater has a greater buoyancy
2. Other Ocean Properties
a. Temperatures at the surface of the ocean vary with locations and seasons.
Gases vary as well.
b. Temperature of Ocean Water
i. The surface of the ocean absorbs energy from the sun
1. Near the equator, surface water reaches 25°C
ii. Warm water is less dense than cold water
1. Warm water forms a thin layer on the ocean surface
iii.Generally, the deeper you descend into the ocean, the colder and denser
the water becomes
c. Gases in Ocean Water
i. Ocean organisms use carbon dioxide and oxygen
ii. Carbon dioxide is about 60 times as plentiful in the ocean as in air
1. Algae and animals like coral need carbon dioxide for photosynthesis
iii.Oxygen is scarcer in the ocean than in air
1. Most plentiful near the surface; amount is affected by the water
temperature
2. Cold water contains more oxygen than warm, tropical waters
3. Changes With Depth
a. The ocean has a vertical section referred to as the water column—shows
dramatic changes
b. Decreasing Temperature
i. As you descend through the ocean, the water temperature decreases
ii. There are three temperature zones in the water column
1. Surface water is warmest, extends to 100-500 meters below the
surface
2. Transition zone extends from the bottom of the surface zone to about
1 kilometer
a. Temperatures drop to about 4°C
3. Deep zone is below the transition zone
4. Average temperature is 3.5°C in most of the ocean
c. Increasing Pressure
i. Pressure increases continuously with depth in the ocean
ii. Divers can descend safely only to about 40 meters
iii.Submersible: an underwater vehicle built of materials that resist pressure
Review
 What is salinity? What is the average salinity of ocean
water?
Review
 Describe one factor that increases the salinity of
seawater and one factor that decreases its salinity.
Review
 How do carbon dioxide and oxygen levels in the oceans
compare to those in the air?