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Chapter 4
Chapter 4
Water, 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
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.
Magical properties of water
• Ice floats
– If it didn’t ice ball earth
• Dissolves ionic compounds
– If it didn’t no electricity in cells
• Adhesion/cohesion (sticky)
– If it didn’t all life would be underwater
• Specific Heat Capacity
Nature of Water
• Freezing point and boiling point
– polar water molecules tend to come together forming hydrogen bonds with one another
– high boiling point reflects energy needed to overcome attractive forces of hydrogen bonds – relative high freezing point (0oC) of water is a
Nature of Water
• Water as a solvent
– polar nature keeps solute’s ions in solution – water cannot dissolve non-polar molecules,
(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
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”
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
• Albedo = measurement of absorbed energy
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
pH paper Neutral pH scale Gastric juice Vinegar Urine Rain water Human saliva Blood Egg white Seawater
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
Quiz
• What are the four organic compounds that
make up all living things?
• Are they acid or base?
• What is more dangerous to us, acid or
base?
– Why?
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 (SO42-)
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)
Quiz
• Does water evaporating from the ocean make the ocean more or less salty?
• Does run-off water (land into ocean) make the ocean more or less salty?
• Does rain make the ocean more or less salty? • Does freezing of ocean water make the ocean
more or less salty?
• Which is more dense, salt water or fresh water?
Salt Water
• Cycling of sea salts
– sea salt originally from earth’s crust
– ocean composition has remained the same due to balance between addition through runoff & removal – salts removed in many ways:
• form insoluble complexes that precipitate to ocean floor • depositing on land by sea spray
• evaporites (salt deposits)
• concentration in tissues of organisms harvested for food • Adsorption - process of ions sticking to surface of fine
Sea spray removes salts Bottom sediments Precipitation Precipitation
Chloride (Cl–)
Sulfate (SO42–)
Hydrogen sulfide (H2S) Chlorine (Cl2)
Volcano
Sulfur
Organisms die
Calcium (Ca2+)
Magnesium (Mg2+)
Potassium (K+)
Rock on the seafloor Clay particles adsorb River discharge
Carbonate (CO32–)
Calcium (Ca2+)
Sulfate (SO42–)
Sodium (Na+)
Magnesium (Mg2+)
Salts removed when organisms are
caught for food
Stepped Art
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
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,
Ocean Heating and Cooling
• Earth’s energy budget
– energy input
• sun’s radiant energy heats earth’s surface
• spherical shape + presence of the atmosphere
Trop
ic of C
apricorn
Greater angle
Less solar energy per unit area
Right angle
More solar energy per unit area
Greater angle
Less solar energy per unit area
Trop
ic of C
ancer Equator
Stepped Art
Ocean Heating and Cooling
• Earth’s energy budget
– energy output
• excess energy absorbed by the earth is transferred to the atmosphere by evaporation and radiation
• accumulation of greenhouse gases (H2O, CO2,
methane, chlorofluorocarbons (CFC’s) NO, NO2) can
Radiation to atmosphere and clouds Convection and conduction to the atmosphere Scattered and deflected by atmosphere Reflected by ground Reflected by clouds Heat transferred via evaporation Absorbed by atmosphere and clouds Absorbed by atmosphere and clouds Radiation from atmosphere Radiation from earth Absorbed by rock, soil, and water on the surface Stepped Art
Ocean Heating and Cooling
• Sea temperature
– temperature varies daily and seasonally
– affected by energy absorption at the surface, loss by evaporation, transfer by currents,
warming/cooling of atmosphere, heat loss through radiation
– seasonal variations in the amount of solar
radiation reaching the earth, occur especially between 40o and 60o N and S because angle of sun’s rays change dramatically at these
Coriolis effect
• In which direction do currents move in the
oceans in the northern hemisphere?
• In which direction do currents move in the
oceans in the southern hemisphere?
• What is the water temp in Florida?
– Warm or cold and why
• What is the water temp in Cali?
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
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
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)
Why do we get clouds?
• Low pressure is warm air rising
– It cools, reaches the dew point and you
get clouds/rain
cold day
• Hot air gives you a cold day!
• High pressure is cold air sinking
– It heats up and actually pulls moisture
from the ground
hot sunny day!
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
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
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
Ocean Layers and Ocean Mixing
• Density—the mass of a substance in a
given volume, usually measured in g/cm
3– density of pure water = 1 g/cm3
– density of salt water = 1.0270 g/cm3
• Density increases when salinity increases
• Density increases when temperature
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
Storms drive surface water deeper
Water column stabilizes Water column stable
Water column unstable Fall Air temperature cools Surface water cools, displaces less dense water Colder denser water Summer
Warm surface water
Thermocline
Spring
Air temperature warms
Surface water warms
Colder denser water Thermocline Isopycnal Wind Winter Stepped Art
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
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
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
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
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
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
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
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
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
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
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
