Warm-Up: 3/4-3/5

• Name 4 properties of water that you remember from biology/ES.

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Chapter 4Chapter 4Water, Waves, and TidesWater, Waves, and Tides

Key Concepts

• The polar nature of water accounts for many of its physical properties.

• Seawater contains a number of salts, the most abundant being sodium chloride.

• Salts are constantly being added to and removed from the oceans.

• The exchange of energy between oceans and the atmosphere produces winds that drive ocean currents and weather patterns.

Key Concepts• The density of seawater is mainly

determined by temperature and salinity.• Vertical mixing of seawater carries oxygen

to the deep and nutrients to the surface.• Waves are the result of forces acting on

the surface of the water.• The gravitational pull of the moon and the

sun on the oceans produces tides.

Nature of Water

• Marine organisms are 70 – 80% water by mass.

• Terrestrial organisms are approximately 66% water by mass!

• Physical properties of water– excellent solvent– high boiling point and freezing point– denser in its liquid form than in its solid form– supports marine organisms through buoyancy– provides a medium for chemical reactions necessary for

life

Nature of Water

• Structure of a water molecule– 2 H atoms bonded to 1 O atom– polar - different parts of the molecule have

different electrical charges• the oxygen atom carries a slight negative charge• the hydrogen atoms carry a slight positive charge

Nature of Water

• Freezing point and boiling point– polar water molecules- Hydrogen bonds– high boiling point reflects energy needed to

overcome attractive forces of hydrogen bonds– relative high freezing point (0oC) of water is a

result of less energy needed to fix molecules into position to form solid

Nature of Water

• Water as a solvent– polar nature keeps solute’s ions in solution– water cannot dissolve non-polar molecules,

e.g., oil and petroleum products

(a) Polar nature of water molecule

(c) Structure of water molecules in a solid state (ice)

(b) Hydrogen bonding of water molecules due to its polarity

(d) Salt crystals dissolving in water

Hydrogen bond

Salt

Stepped Art

Fig. 4-1, p. 70

Nature of Water• Cohesion, adhesion, and capillary action

– hydrogen bonds cause water molecules to be cohesive, i.e., stick together, accounting for high surface tension

– adhesion - attraction of water to surfaces of objects that carry electrical charges, making them “wet”

– adhesion also accounts for water’s capillary action - the ability of water to rise in narrow spaces

Nature of Water

• Specific heat (Thermal capacity)– water has a high specific heat (amount of heat

energy needed to raise 1 g 1o C) due to hydrogen bonds

– ocean can maintain relatively constant temperature

• Water and light– much light reflected into the atmosphere– different wavelengths (colors) of light penetrate

to different depths

Nature of Water• Chemical properties of water

– acids release H+ atoms in water– bases bind H ions and remove them from

solution– pH scale measures acidity/alkalinity– pH of pure water is 7, considered neutral– ocean’s pH is slightly alkaline (average 8)

owing to bicarbonate and carbonate ions– organisms’ internal and external pH affect life

processes such as metabolism and growth

pH paper

Neutral

pH scale

Gastric juice

Vinegar

UrineRain waterHuman salivaBloodEgg whiteSeawater

Great Salt Lake

Liquid soap

Oven cleaner

Increasing acidity

Increasing alkalinity

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14 Stepped Art

Fig. 4-4, p. 72

Salt Water• Composition of seawater

– most salts present in seawater are present in their ionic form

– 6 ions make up 99% of dissolved salts in the ocean:• sodium (Na+)• magnesium (Mg2+)• calcium (Ca2+)• potassium (K+)• chloride (Cl-)• sulfate (SO4

2-)

– trace elements - present in concentrations of less than 1 part per million

Salt Water• Salinity

– seawater = 3.5% salt, 96.5% water– expressed as in g per kg water or parts per

thousand (ppt)– salinity of surface water varies as a result of

evaporation, precipitation, freezing, thawing, and freshwater runoff from land

– between 10o N-10o S of equator = low salinity (due to heavy rainfall)

– areas around 30o N and 30o S = high salinity (evaporation > precipitation)

– from 50o = low salinity (heavy rainfall)– poles = high salinity (freezing – removes water

from sea)

Sea sprayremoves

salts

Bottom sediments

Precipitation

Precipitation

Chloride (Cl–)Sulfate (SO4

2–)

Hydrogen sulfide (H2S)

Chlorine (Cl2)

Volcano

Sulfur

Organismsdie

Calcium (Ca2+)Magnesium (Mg2+)

Potassium (K+)

Rock onthe seafloor

Clay particlesadsorb

Riverdischarge

Carbonate (CO32–)

Calcium (Ca2+)Sulfate (SO4

2–)

Sodium (Na+)Magnesium (Mg2+)

Salts removedwhen organisms are

caught for food

Stepped Art

Fig. 4-6, p. 75

Salt Water

• Gases in seawater– gases from biological processes

• oxygen is a by-product of photosynthesis

• release of CO2 from respiration

• oxygen-minimum zone – located just below sunlit surface waters

– solubility of gases in seawater• seawater has more O and CO2 but less N than the

atmosphere

• relative solubility in seawater: CO2 > O > N

• affected by temperature, salinity and pressure

Salt Water

• role of bicarbonate as a buffer– bicarbonate formed from the solution of CO2

– buffer - a substance that can maintain the pH of a solution at a relatively constant point

– bicarbonate’s buffering action helps maintain the pH of seawater at a constant value, providing a stable environment for marine organisms

Ocean Heating and Cooling

• Earth’s energy budget– energy input

• sun’s radiant energy heats earth’s surface• energy decreases with latitude (seasons)

– energy output• Absorbed energy is released into atmosphere• Greenhouse (CO2, Mthane) gasses trap energy

Tropic of Capricorn

Greater angleLess solar energyper unit area

Right angleMore solar energyper unit area

Greater angleLess solar energyper unit area

Tropic of Cancer

Equator

Stepped Art

Fig. 4-8, p. 77

Winds and Currents

• Winds– result from horizontal air movements caused

by temperature, density, etc.– as air heats, its density decreases and it rises;

as it cools, density increases and it falls toward earth

– wind patterns: upper air flow from the equator towards the north and south

Winds and Currents

• Winds– Coriolis effect

• a point rotating at the equator moves faster than a point at a higher latitude

• path of air mass appears to curve relative to the earth’s surface—to the right in the Northern Hemisphere, left in the Southern

Winds and Currents

• Surface wind patterns– 3 convection cells in each hemisphere:

• northeast & southeast trade winds• westerlies• polar easterlies

– areas of vertical air movement between wind belts

• Doldrums (at equator)• horse latitudes (at 30o N & S)

Winds and Currents

• Ocean currents– surface currents

• driven mainly by trade winds (easterlies and westerlies) in each hemisphere

• Coriolis effect– currents deflected to the right of the prevailing wind

direction in the Northern Hemisphere, to the left in the Southern Hemisphere

– deflection can be as much as 45-degree angle from wind direction

• gyres—water flow in a circular pattern around the edge of an ocean basin

Winds and Currents

• Classification of currents– western-boundary currents: fastest, deepest currents

that move warm water toward the poles in each gyre (e.g. Gulf Stream)

– eastern-boundary currents: slow moving, carry cold water toward the equator

– transverse currents: connect eastern- and western-boundary currents in each gyre

– biological impact• western-boundary currents not productive, carry little

nutrients, but increase oxygen mixed in water• eastern-boundary currents productive, nutrient-rich

Winds and Currents• Currents below the surface

– energy transferred from winds to surface water is transferred to deeper water

– deeper-water currents are deflected by the Coriolis effect, down to about 100 m

– friction causes loss of energy, so each layer moves at an angle to and more slowly than the layer above, creating an Ekman spiral

– Ekman transport—net movement of water to the 100-m depth

Ocean Layers and Ocean Mixing

• Density—the mass of a substance in a given volume, usually measured in g/cm3 – density of pure water = 1 g/cm3 – density of salt water = 1.0270 g/cm3

• Density increases when salinity increases

• Density increases when temperature decreases

Ocean Layers and Ocean Mixing• Characteristics of ocean layers

– depth 0-100 m (330 feet): warmed by solar radiation, well mixed

– 100-1,000 m: temperature decreases– thermocline – zone of rapid temperature change– halocline: salinity increases 0-1,000 m– pycnocline: 100-1,000 m, where changes in

temperature and salinity create rapid increases in density

– seasonal thermoclines

Storms drive surfacewater deeper

Water column stabilizes

Water column stable

Water column unstable

Fall

Air temperaturecools

Surface watercools, displaces

less densewater

Colder denserwater

Summer

Warm surface waterThermocline

Spring

Air temperature warms

Surface water warms

Colder denserwater

Thermocline

Isopycnal

Wind

Winter

Stepped Art

Fig. 4-19, p. 86

Ocean Layers and Ocean Mixing• Horizontal mixing

– higher density causes water at 30o N to form a curved layer that sinks below less-dense equatorial surface water and then rises to rejoin the surface at 30o S

– even denser water curves from 60o N to 60o S below other surface waters

– winter temperatures and increased salinity owing to freezing result in very dense water at the poles, which sinks toward the ocean floor

Ocean Layers and Ocean Mixing

• Vertical mixing– vertical overturn results when denser water at

the top of the water column sinks while less-dense water rises

– isopycnal—stable water column that has the same density from top to bottom

– vertical mixing allows water exchange between surface and deep waters

– nutrient-rich bottom water is exchanged for oxygen-rich surface water

Ocean Layers and Ocean Mixing• Upwelling and downwelling

– equatorial upwelling• water from currents on either side of the equator is

deflected toward the poles, pulling surface water away to be replaced by deeper, nutrient-rich water

– coastal upwelling• Ekman transport moves water offshore, to be

replaced by deeper, nutrient-rich water

– coastal downwelling• coastal winds force oxygen-rich surface waters

downward and along the continental shelf

Ocean Layers and Ocean Mixing

• Deepwater circulation– differences in density, not wind energy, cause water

movement in deep oceans– densest water of all is Antarctic Bottom Water, mostly

formed in winter in the Weddell Sea– dense Antarctic water sinks to the bottom and moves

slowly toward the Arctic– some North Atlantic Deep Water moves into the North

Atlantic via a channel east of Greenland– high-salinity Mediterranean Deep Water flows through

the Strait of Gibraltar into the Atlantic Ocean

Waves

• Wave formation– wave: a flow of energy or motion, not a flow of

water– generating force: a force that disturbs the

water’s surface, e.g., wind, geological events, falling objects, ships

– restoring force: the force that causes the water to return to the undisturbed level

• surface tension for capillary waves• gravity for gravity waves

Waves• Types of waves

– Progressive (forced) waves are generated by wind and restored by gravity, progress in a particular direction

• forced waves are formed by storms, which determine their size and speed

• free waves, no longer affected by the generating force, move at speeds determined by the wave’s length and period

• swells are long-period, uniform free waves which carry considerable energy and can travel for thousands of km

Waves• Types of Waves (con’t)

– deepwater and shallow-water waves• deepwater waves—waves that occur in water that

is deeper than ½ of a wave’s wavelength

– breakers• deepwater waves become shallow-water waves

when they move into shallow water• surf zone—area along a coast where waves slow

down, become steeper, break, and disappear• breakers form when the wave’s bottom slows but

its crest continues at a faster speed

Waves

• Types of Waves (con’t)– Tsunamis (large seismic sea waves)

• seismic sea waves are formed by earthquakes• tsunamis have long wavelengths, long periods and

low height• compression of the wave’s energy into a smaller

volume upon approaching a coast pr island causes a dramatic increase in height

Tides• Tides: periodic changes in water level

occurring along coastlines• Why tides occur

– tides result from the gravitational pull of the moon and the sun

– though smaller, the moon is closer to earth, so its gravitational pull is greater

– water moves toward the moon, forming a bulge at the point directly under it

– the centrifugal force opposite the moon forms another bulge

– areas of low water form between bulges

Tides

• Spring and neap tides– during spring tides, the times of highest and

lowest tides, the earth, moon and sun are in a line and act together creating highest and lowest tides

– when the sun and moon are at right angles, the sun’s pull offsets the moon’s, resulting in neap tides, which have the smallest change between high and low tide

Tides

• Tidal range– diurnal tide: one high tide and one low tide each

day– semidiurnal tide: two high tides and two low

tides each day (most common)• mixed semidiurnal tide: high and low tides are at

different levels

– flood tides are rising; ebb tides are falling– tidal currents are associated with tidal cycle– slack water occurs during the change of tides