Transcript Chapter 4

Chapters 6 & 7
Water
Importance of Water
Most abundant component of living things
– Marine organisms: 70-80% water by mass
– Terrestrial organisms: 66% water by mass
Provide buoyancy and a medium to
marine organisms
High heat capacity influences overall
climate of Earth
Physical Properties
Excellent solvent
High boiling point and freezing point
More dense in liquid form than in solid
Provide buoyancy and a medium to
marine organisms
Structure of Water
Water is formed as the result of a covalent bond
between 2 hydrogen atoms and one oxygen atom
Covalent bond: bond formed by sharing of electrons
Water is a Polar Molecule
Polar Molecule: a
molecule that has a
slightly positive charge at
one end, and a slightly
negative charge at one
end
Caused by unequal
sharing of electrons
Oxygen is more
electronegative than
Hydrogen
Water Molecules Form Hydrogen
Bonds
Hydrogen Bond: weak
attraction between the
positive hydrogen end
of one water molecule
and the negative
oxygen end of
another water
molecule
Properties of Water Influenced by
Hydrogen Bonding
High heat capacity
High boiling point
High freezing point
Adhesion
Cohesion
Density of ice
High Heat Capacity
Heat Capacity: the amount of heat
required to change the temperature of a
substance.
Hydrogen bonding gives water its high
heat capacity
Allows water to store and carry a
tramendous amount of heat energy
Provides a stable environment for marine
organisms
Freezing and Boiling Point
High boiling point reflects the large amount
of energy it takes to break the hydrogen
bonds
High freezing/melting point indicates that a
large amount of energy is required to
overcome the hydrogen bonds that hold
water molecules in position to form a solid.
Cohesion
Def: The attraction of water molecules to
other water molecules
Gives water a high surface tension
– Surface molecules have a higher attraction for
other water molecules than for air molecules
Adhesion
Occurs when water is attracted to surface
objects that carry an electrical charge
Ability of water to get things wet
Ability of water to rise in narrow spaces
– Capillary action
Water and Light
Water has an ability to selectively absorb
certain wavelengths of light.
– Low energy wavelengths are quickly
absorbed
– High energy wavelengths penetrate deeper
– Atlantic Ocean
55% of the light is absorbed within 1 meter
– Clear water
Less than 1% of light entering can penetrate
deeper than 100 meters
Light Spectrum Absorption by
Water
Chemical Properties
Classified as acids or bases
– Acids: release H+ when added to water
– Bases: Bind H+ and remove them from
solution
pH Scale
– Indicator of the number of H+ in a volume of
solution
– Ranges from 0-14
>7 Acid
<7 Base
pH of Water
pH of pure water is 7
Ocean water
– Determined by the substances that are
dissolved in it
– Slightly alkaline
Average pH of 8
Due to seawater containing large amounts of
bicarbonate and carbonate
Salt water
Named so because of the high quantity of
dissolved salts compared to freshwater
Salinity of ocean water is important
– Environmental factor that strongly influences
marine organisms
– Dissolved substances dictate the distribution
and kinds of marine organisms in a certain
environment
Saltwater Composition
Most salts present in their ionic form
99% made up of Na+, Mg2+, Ca2+, K+, Cland SO42+
Trace elements
– Present in concentration of less than one part
per million
Principle of Constant Proportions
Proportions of several key inorganic elements
and compounds dissolved in seawater DO NOT
CHANGE, regardless of overall salinity.
Useful to marine scientists, because if you know
how much of one element there is, you can
determine how much there is of all the others.
Only the amount of water, and therefore the
salinity, changes.
Salinity
Seawater
– 3.5% salt
– 96.5% water
– Average salinity of 35 parts per thousand
NaCl is the most common salt present
Affected by evaporation and precipitation
Can change in certain location
– Higher salinity around the poles
Sea Salt Cycling
Original sources
– Rocks and other parts of the Earth’s crust and
interior
Processes that contribute
– Rocks release ions as they are broken down
– Volcanic eruptions
– River water/runoff
Gases in Seawater
Oxygen, nitrogen and carbon dioxide
Dissolve at the surface of the sea from the
atmosphere and are introduced by
biological processes
Gases from Biological Processes
Gases are produced as by-products
– Photosynthesis: Oxygen
Added only near the surface
– Decomposition: Carbon dioxide
Add at all depths
Oxygen-minimum zone
– Just below the sunlight surface waters
– Area where oxygen is depleted by the
resident animal life but not replaced by
photosynthesis
Solubility of Gases
Amount of oxygen and carbon dioxide in
seawater is greater than it is in the
atmosphere.
Amount of nitrogen is less.
Amount of gas that water can hold
depends on
– Temperature
– Salinity
– Pressure
Solubility of Gases
Cold water hold more gas than warm
Low salinity allows more gas to dissolve
Day Two
Uneven Heating of the Earth
3 primary causes
– Earth is spherical
– Axis of rotation is tilted
– Distance from the sun varies throughout the
year
Let’s take a closer look.
Angle of Incidence
Light from a single
source doesn’t strike
a sphere evenly
Small part receives
perpendicular light
rays, while other parts
receive slanted light
rays
Orbital Inclination
Axis is tilted at 23.5°
Equator doesn’t receive perpendicular light
rays all year
Perpendicular rays travel between the
Tropic of Cancer (23.5°N) and the Tropic
of Capricorn (23.5°S)
Causes the seasons
Elliptical Orbit
Receives more heat when the orbit is closer to
the sun
Little effect on the temperature
– Closer to the sun in the winter (Northern Hemisphere)
Biological Importance
Autumn color change
of leaves
Terrestrial birds and
other animals migrate
Gray whale migration
in the ocean
Convection
The vertical movement of currents caused
by temperature differences in a fluid
Results when the sun warms the air in
contact with it, and the air rises
The warm rising air is replaced by cooler
dense air
Causes a global wind pattern between the
poles and the equator
Coriolis Effect
The tendency for the path of a moving
object to deflect to the right in the Northern
Hemisphere and the left in the Southern
Hemisphere
Explains why we have winds in all
directions
Influences ocean currents
Major factor in distributing heat, nutrients
and types of life
Coriolis Effect
Caused by the Earth’s
rotation
Greater at higher
latitudes
Along the equator, the
effect is zero
Air and the Coriolis Effect
Deflects the air to the right as it travels in
the Northern Hemisphere and to the left in
the Southern Hemisphere
Atmospheric circulation cells
– Regions of wind patterns
– Make up 6 distinct air masses with individual
flow patterns
Hadley Cells
Most important atmospheric circulation
cells
Found between the equator and 30°N or S
latitude
Responsible for the trade winds
Ferrel Cells
Found between 30° and 60° latitude
Creates the westerlies
– Blow toward the east
Important to sailing vessels trying to reach
Europe
Polar Cells
Lie between 60° and the poles
Sends cooler air back down towards the
equator
Produce the polar easterlies
Ocean Currents
Produced when wind blowing across the
ocean surface pushed and pulls the water,
causing it to move
Move water in predictable patterns within
ocean basins
Surface Currents
Winds transfer energy to water by friction
– Produces waves that transfer energy to water
– Cause mass of water beneath the moving air
flow
Forms a surface current
Main driving forces are the trade winds
Gyres
Water flows in a circular pattern around
the edge of an ocean basin
5 major in the world
– 3 in the Southern Hemisphere
– 2 in the Northern Hemisphere
Current Classification
Distinguished on the basis of
– Distinct temperatures
– Flow characteristics
– Position
Western-boundary Currents
Fastest and deepest currents
Found along western boundaries of ocean
basins
Move warm water toward the poles
Carry little nutrients-not productive
Move large volumes of water
Gulf Stream
Eastern-boundary Currents
Carry cold water toward the equator
Slow moving
Move smaller volumes of water
More productive
Contribute to nutrient mixing of surface
waters
Transverse Currents
Connect eastern and western boundary
currents
Each current flows uninterrupted into the
next
Currents Beneath the Surface
Movement caused by friction
Coriolis effect applies
Each layer slides horizontally over the layer
beneath it
– Lower layers move slower
Ekman spiral
– Spiral flow of water that results from the movement of
the layers
Ekman transport
– Net movement of water to 100 m depth