Ch 15.1 The Compositon of Seawater

Ch 15.1 The Composition of Seawater

Vocabulary

• salinity
• thermocline
• density
• pycnocline
• mixed zone

Objectives:

1.  Know the composition of seawater and the units used to express the salinity

Most of the salt in sea water is sodium chloride (NaCl), common table salt.  Because the proportion of dissolved substances in seawater is such a small number, scientists typically express salinity in parts per thousand (0/00)

The average salinity of seawater is 3.5 % or 35 0/00

2.  What are the two main sources of salt water in the ocean?

1. Chemical weathering of rocks
2. Earth’s interior (volcanic eruptions)

3.  What factors affect the density of ocean water?

• salinity
• temperature

From our lab the water masses listed from least to most dense are

• warm fresh
• cold fresh
• warm salt
• cold salt

Salinity is decreased by increasing the water content.  This can occur by the following processes.

1. precipitation
2. surface run off
3. sea ice melting
4. ice bergs melting

Salinity can increase by decreasing the water content.  This can occur by

1. evaporation
2. sea ice forming

4.  What are the three main zones of the open ocean?  See page 427 for a sketch.

Surface zone Because solar energy is received here, this is the warmest layer.  The “mixed zone” is the area on the surface created buy the mixing of water by waves, tides, and currents.  The temperature is nearly uniform but varies according to latitude.  The surface mixed zone comprises only about 2 % of ocean water.

Transition zone Below the sun warmed zone of mixing, the temperature falls abruptly with depth.  This layer includes an thermocline and pycnocline.  This zone comprises about 18 % of the total ocean water.

Deep zone sunlight never reaches this zone and the temperature is just few degrees above freezing.  The density is constant and high.  This zone is about 80 % of the ocean water.

Questions:

Salinity and temperature both affect the density of sea water.

Salinity can be decreased by ______________the amount of fresh water in the ocean.

List 4 processes that decrease the density of sea water

1

2

3

4

Salinity of sea water and be increased by _________________ the amount of fresh water in the ocean.

Two natural processes that cause this are

1

2

Density of sea water increases and temperature ____________________.

Depth and latitude are two factors that affect sea water temperature.

The deeper the depth, the _______________________ the temperature

The greater the latitude, the _______________________ the temperature.

Of the three zones of the ocean, which zone contains the greatest percent of all ocean water?

Which layer contains the thermocline and pycnocline?

What three factors “mix” the water in the surface zone?

Which of the 3 ocean layers is the most dense?  Explain.

Why is do thermocline or pycnoclines NOT exist in the deep zone?

.