Chapter 5 Water and Seawater

Essentials of Oceanography

7th Edition

Atomic structure

Atoms are the building blocks of all matter

Nucleus contains:Neutrons (no charge)

Protons (+ charge)

Outer shell(s) contain:Electrons (– charge) Figure 5-1

The water molecule

Composed of 1 oxygen and 2 hydrogen atoms (H20)

Contains strong (covalent) bonds between atoms

Unusual bend in geometry

Has polarity (oppositely charged ends)

Figure 5-2a

Interconnections of water molecules

Polarity causes water molecules to form weak (hydrogen) bonds between water molecules

Water sticks to itself and to other substances

Allows water to be the universal solvent Figure 5-3

Water as a solvent

Water dissolves table salt (NaCl) by attracting oppositely charged particles

Pulls particles out of NaCl structure to dissolve it

Figure 5-4

Water in the 3 states of matter

Latent (hidden) heat = energy that is either absorbed or released as water changes state

Figure 5-5

The ocean moderates coastal temperatures

Water has high heat capacity, so it can absorb (or release) large quantities of heat without changing temperatureModerates coastal temperatures Figure 5-6

Hydrogen bonds in H2O

Figure 5-8

The formation of ice

As water cools to 4°C:Molecules slowWater contractsDensity increases

Below 4°C:Hydrogen bonds formWater expands

As water freezes:Expands by 9%

Figure 5-11

Snowflake geometry

All snowflakes have 6-sided geometryCaused by water’s polarity and ability to form hydrogen bonds

Figure 5-12

Salinity

Salinity = total amount of solid material dissolved in water

Can be determined by measuring water conductivity

Typically expressed in parts per thousand (‰)

Figure 5-15

Constituents of ocean salinity

Average seawater salinity = 35‰Main constituents of ocean salinity:

Chloride (Cl–)Sodium (Na+)

Sulfate (SO42–)

Magnesium (Mg2+)Figure 5-13

Salinity variations

Location/type Salinity

Normal open ocean 33-38‰

Baltic Sea 10‰ (brackish)

Red Sea 42‰ (hypersaline)

Great Salt Lake 280‰

Dead Sea 330‰

Tap water 0.8‰ or less

Premium bottled water 0.3‰

Ocean buffering

Ocean pH = 8.1 (slightly basic)

Buffering protects the ocean from experiencing large pH changes

Figure 5-18

Processes affecting seawater salinity

Processes that decrease seawater salinity:PrecipitationRunoffIcebergs meltingSea ice melting

Processes that increase seawater salinity:Sea ice formingEvaporation

The hydrologic cycle

Figure 5-19

Surface salinity variation

Pattern of surface salinity:

Lowest in high latitudesHighest in the tropicsDips at the Equator

Surface processes help explain pattern

Figure 5-20

Surface salinity variation

High latitudes have low surface salinityHigh precipitation and runoff

Low evaporation

Tropics have high surface salinityHigh evaporation

Low precipitation

Equator has a dip in surface salinityHigh precipitation partially offsets high evaporation

Global surface salinity

Figure 5-21

Salinity variation with depth

Curves for high and low latitudes begin at different surface salinitiesHalocline = layer of rapidly changing salinityAt depth, salinity is uniform Figure 5-22

Seawater density

Factors affecting seawater density:Temperature ↑, Density ↓ (inverse relationship)

Salinity ↑, Density ↑

Pressure ↑, Density ↑

Temperature has the greatest influence on surface seawater density

Density and temperature variations with depth

Figure 5-24

Pycnocline and thermocline

Pycnocline = layer of rapidly changing density

Thermocline = layer of rapidly changing temperature

Present only in low latitude regions

Barrier to vertical mixing of water and migration of marine life

Ocean layering based on density

Mixed surface layer (surface to 300 meters)Low density; well mixed by waves, currents, tides

Upper water (300 to 1000 meters)Intermediate density water containing thermocline, pycnocline, and halocline (if present)

Deep water (below 1000 meters)Cold, high density water involved in deep current movement

Seawater desalination

Desalination methods:

DistillationSolar

Heat

Electrolysis

Reverse osmosis

Freeze separation

Figure 5-25

Distillation

Reverse Osmosis

Figure 5-26

End of Chapter 5

Essentials of Oceanography

7th Edition