Chemical and
Physical Features
of Seawater and
the World Ocean
The “Weather” of the Marine
Environment
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Wind
Waves
Tides
Currents
Temperature
Salt
• Where organisms are found in the marine
environment is determined by the chemical and
physical factors
• To understand the biology of marine organisms,
we must know something about the environment
in which they live
The Waters of
the Ocean
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Marine organisms are mostly made of water
80% or more by weight in most cases
Jellyfish – 95%
Water makes life possible
The Unique Nature of Pure Water
• All matter is made of atoms
• Elements – made of a single kind of element
• Molecules – two or more atoms joined together – ex.
Water
• Water molecules stick together because of their polarity
• These weak bonds are known as hydrogen bonds
• Hydrogen bonds make water different from any other
substance on earth
Three States of Matter
• Solid, liquid, gas
• Water is the only substance that naturally occurs
in all three states on earth
Special Characteristics of Water
• In liquid water hydrogen bonds hold most of the
molecules together in small groups
• Temperature is a reflection of the average speed
of the molecules – faster they move the higher
the temperature
• When the molecules move fast enough they
escape the hydrogen bonds and enter the
gaseous phase (evaporation)
• In water vapor the molecules are not held
together by hydrogen bonds
• As water cools the molecules pack closer
together and take up less space
• Therefore the density of water increases as water
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cools until it reaches 4 C
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• Below 4 C water becomes less dense
• Cool seawater will sink since it is denser
• Once water cools hydrogen bonds reform
• Ice crystals (solid made of regular patterns of
molecules)
• Water molecules are spaced farther apart than in
liquid water making ice less dense than water
• Ice will float on top of water – special property
that makes life in the water possible – insulates
water below
Heat and Water
• It takes a large amount of heat to melt ice
• As heat energy is added and the temperature of
ice rises, the molecules vibrate faster, breaking
some of the hydrogen bonds that hold the crystal
together
Latent Heat of Melting
• Amount of heat required
to melt a substance
Melting Ice
• Once ice begins to melt added heat breaks more
hydrogen bonds rather than increasing the speed of
molecular motion
• Any heat put in goes into melting the ice, not into
raising the temperature
Heat Capacity
• Amount of heat needed to raise a substance’s
temperature by a given amount
• How much heat a substance can absorb
• Water has one of the highest heat capacities of
any substance
Importance of Water’s High Heat
Capacity
• Most marine organisms are not subjected to the
rapid and sometimes drastic temperature
changes that occur on land
Latent Heat of Evaporation
• The amount of heat energy that is needed to
evaporate a substance
• Change from a liquid to a gas
• Water absorbs a great deal of heat when it
evaporates
Water as a Solvent
• Universal solvent
• Especially good at dissolving salts
• Salts are made of combinations of particles that
have opposite electrical charges
• The polarity of water allows it to break down the
salts
• Ion – electrically charged particles
• Ions have stronger charges than the ends of water
molecules
• When a salt enters water the ions break apart and
become surround by water molecules which break there
hydrogen bonds to surround the ion
• Ions pull apart or dissociate and the salt dissolves
Seawater
• Characteristics of seawater are due both to the
nature of the pure water and to the material
dissolved in it
Solids Dissolved in Seawater
• Come from the chemical weathering of rocks on land
and are carried to the sea by rivers
• Earth’s interior
– Hydrothermal vents
– Volcanoes
Salt Composition
• Solutes – dissolved materials
• 6 ions compose over 99% of the solids dissolved in
seawater
• Na and Cl account for 85% of the dissolved solids
in seawater
Salinity
• Total amount of salt
dissolved in seawater
• Usually expressed as the
number of grams of salt
left behind when 1,000
grams of seawater are
evaporated
1 = dissolved trace elements
• Ions are good conductors of electricity
• Electrical conductivity of seawater therefore
reflects the concentration of dissolved ions
• Practical Salinity Units – psu – measurement of
salinity determined from conductivity
measurements
Importance of Salinity
• Salinity of water greatly affects the organisms that
in it
Rule of Constant Proportions
• Percentage of various ions in seawater remains
constant even though the total amount of salt in
the water can vary slightly
• Oceans are chemically well mixed and ocean
salinity varies almost entirely as a result of the
addition or removal of pure water rather than the
addition or removal of salt
Addition and Removal of Water
• Water is removed from the ocean primarily by
evaporation and to a lesser extent by freezing
• Water is added to the ocean by precipitation
Average Salinity of the Ocean
• 35 ppt (parts per thousand)
• Red Sea 40 ppt
• Baltic Sea 7 ppt (from river runoff)
Salinity, Temperature and Density
• The saltier the water the
denser it is
• The density of seawater
therefore depends on its
temperature and its
salinity
Measuring Temperature and Salinity
• Can be measured by lowering specially designed
bottles and thermometers on a wire to the desired
depth
• A weight called a messenger is released to slide
down the wire, triggering the bottles to snap shut and
trap a water sample
Temperature Profile
• A graph that shows the
temperature at different
depths in the ocean
• Water column – vertical
shaft of water
Modern Technology
• Oceanographers usually use electronic sensors to quickly
and accurately record salinity, temperature and depth
throughout the water column, rather than at certain depths
• CTDs – Conductivity Temperature Depth meters
• XBTs – Expendable bathythermographs – measure
temperature
Problem
• Measurements can only be made at one place at one
time – difficult to get information over a large area
• Ship had to move to a new place to make more
measurements
• Conditions change because of currents or weather
• Many ships would help but it is expensive
Part Solution
• Make measurements with automated
instruments that are left in the ocean
• Satellites can measure surface conditions
Dissolved Gases
• Gases are dissolved in seawater as well as solid
materials
• The 3 most important gases are: oxygen, carbon dioxide
and nitrogen
• Found in the atmosphere and dissolve at the sea surface
Gas Exchange
• movement of gases between the atmosphere and the
ocean surface
• Gases dissolve better in cold than warm water
• Dissolved gas concentrations are higher in polar
waters than in the tropics
Oxygen
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Not very soluble
0 to 8 milliliters per liter of seawater
On average 4 to 6 ml/L
Air has 210 ml/L
Carbon Dioxide
• More soluble than oxygen because it reacts
chemically when it dissolves
• 80% of the dissolved gas in the ocean
• .04% in air
• Stores more than 50 times as much total CO2 as
the atmosphere
Transparency
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Biologically important property
Sunlight can penetrate into the ocean
Allows for photosynthesis
Not all colors penetrate seawater equally well
Water is most transparent to blue light
• As depth increases more colors are filtered out
• Red is the first to be filtered out
• Something that is red at the surface looks black or gray at
depth because there is no red light to reflect off them and
be seen
• At depths of 1000 m or 3300 ft there is total darkness
Turbidity
• Transparency of water is strongly affected by material
that is suspended and dissolved in the water
• Ex. Muddy water, lots of plankton
Pressure
• Factor that changes dramatically with depth
• On land – 1 atm of pressure
• With each 10m (33 ft) of increased depth another
atmosphere of pressure is added
• As the pressure increases the gases are compressed –
limits range of orgs – ex. Swim bladder
Water Density
and the Three
Layered Ocean
• Much of the three dimensional structure of the
sea, especially in relation to depth is controlled by
the density of the water
Stability and Overturn
• Densest water sinks so the ocean is usually
layered or stratified
• Deep water – cold and dense
• Surface water – warm and light
Water Column Stability
• Stable Water Column - Less dense on top, dense
on bottom
• Low stability – surface water is only slightly less
dense
• Highly stable – large density difference
• Unstable – surface water more dense than
bottom water
• Downwelling – when surface water sinks
• Overturn – when dense surface water displaces
deeper water
• Temperature and density profiles are vertical
straight lines for water columns experiencing
overturn
• Overturn usually occurs in temperate and polar
regions during the winter when the surface water
cools
• The water descends to a depth determined by its
density
• The processes that change salinity in the open
ocean (precipitation, evaporation and freezing)
occur only at the surface
• Temperature changes occur only at the surface
Water Mass
• Once surface water has sunk its properties do not
change
• The volume of water has a “fingerprint”, a
characteristic combination of temperature and
salinity
• Oceanographers can tract the movement or
circulation of water masses
Thermohaline Circulation
• Circulation driven by changes in density which in turn is
determined by temperature and salinity
• Extend throughout the ocean depths
• Important in regulating earth’s climate and chemically
mixing the oceans
• Brings dissolved oxygen to the deep sea
• Helps determine the abundance of life in the deep sea
The ThreeLayered Ocean
Surface Layer
• 100 to 200 m thick (330 to 660 ft)
• Mixed by wind, waves and currents
• Also known as the mixed layer
Thermocline
• Sudden changes in temperature over small depth
intervals
• seasonal
Intermediate Layer
• Below the surface layer of around 1500 m
(5000 ft)
• Contains the main thermocline
Main Thermocline
• zone of transition between warm surface water
and cold water below
• lies in the intermediate layer
• rarely breaks down
• feature of the open ocean
Deep and bottom layers
• Below 1,500 m or (5,000 ft)
• Uniformly cold
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• Typically less than 4 C (39 F)
Motion in the
Ocean
Surface Circulation
• Most intense motion of the ocean occurs at the
surface in the form of surface currents and waves
• Driven by wind which is driven by heat from the
sun
• Coriolis effect also strongly influences
Coriolis Effect
• Earth is round and rotating so anything that
moves over its surface tends to turn a little rather
than moving in a single straight line
• Mostly effects winds and ocean currents that
move over large distances
• Northern Hemisphere – deflects things to the
right
• Southern Hemisphere – deflects things to the left
Winds Patterns
• Winds in our atmosphere are driven by heat
energy from the sun
• Most of the solar energy is absorbed near the
equator
• Warm air rises at the equator
• Air from adjacent areas gets sucked in to replace
the rising equatorial air creating wind
• The wind does not move straight to the equator
but are bent by the Coriolis effect – approach at a
45 angle
Trade Winds
• winds near the equator (northeast and the
southeast)
• steadiest winds on earth
• between 0 and 30 degrees
Westerlies
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driven by solar energy
more variable
between 30 and 60 degrees
move in the opposite direction to the trade winds
Polar Easterlies
• Most variable
• Between 60 and 90 degrees
Surface Currents
• The major wind fields of the atmosphere push the
sea surface creating currents
• All major surface currents of the open ocean are
driven by the wind
• When pushed by the wind the uppermost layer of
water begins to move
• The water does not move in the same direction
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as the wind but at a 45 angle because of the
Coriolis effect
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• The top layer pushes the water below but at a 45
angle and so on
Ekman Spiral
• Spiral change in the movement in the water
column when the water is pushed by the wind
• At a depth of a few hundred meters the wind in
not felt at all
• Ekman Layer – upper part of the water column
that is affected by the wind
• Ekman transport – taken as a whole the Ekman
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layer moves at 90 from the wind direction
Consequence of the Coriolis Effect
• Trade winds move towards the equator the
equatorial currents that these winds produce
move parallel to the equator
Gyres
• Wind driven surface currents combined into huge
more less circular systems
• Under the influence of the Coriolis Effect
Transportation of Solar Heat
• Warm currents on the western sides of the gyres
carry vast amounts of solar heat from the equator
to higher latitudes
• Cold currents flow in opposite direction on the
eastern sides
• Ocean currents act as a giant thermostat
warming the poles and cooling the tropics
• Large scale fluctuations in current patterns can
dramatically effect weather around the world - El
Nino
Role of Surface Currents
• Surface water temperatures are higher on the
western sides of the oceans where currents carry
warm water away from the equator
Waves
Waves
• Wind causes
• Most familiar of all ocean phenomena
• Affect the organisms that live on the shore
Wave Parts
• Crest – highest part of a wave
• Trough – lowest part of a wave
• Wave Height – vertical distance between trough
and crest
• Wavelength – distance between two successive
crests or troughs
• Period – time a waves takes to go by any given
point
Water Movement
• In a wave crest, water moves up and forward
• In a wave trough, water moves down and back
• On the whole water particles do not go anywhere
at all – just move in circles
• Waves carry energy across the surface, not water
Formation of waves
• Begins when the wind starts to blow
• The faster and longer the wind blows the larger
the waves get
• Fetch – span of open water over which the wind
blows – determines size of waves
Seas
• waves that have sharp peaks and relatively flat
wave troughs
Swells
• Waves with smooth rounded crests and troughs
• Similar to ideal waves
Surf
• Waves that becomes so
high and steep as it
approaches the shoreline
that it breaks
• Waves become closer
together
• Energy is released on the
shoreline when the wave
breaks
Tsunamis
• Deadly waves
• Japanese word for “harbor wave”
• Produced by earthquakes, landslides, volcanoes,
and other disturbances of the sea floor
• Tidal waves – properly called – seismic sea
waves
• Long fast moving waves
• Wavelengths of 240 km (150 mi)
• Travel 700 km/hr (435 mi/hr) – as fast as a jet
plane
• Open ocean – not very high – 1 m
Warning
• Worldwide network of seismic monitoring stations that
provide instant notice of an earthquake or other seismic
disturbance
• System has saved lives but is far from perfect
• Can’t predict which earthquakes produce killer tsunamis
• Also many people in developing countries do not get the
warnings
Tides
Tides
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Dominant influence on near shore sea life
Expose and submerge organisms on the shore
Drive the circulation of bays and estuaries
Triggers spawning
Causes of the Tides
• Caused by the gravitational pull of the moon and
sun by rotations of the earth moon and sun
• Earth and the moon rotate around a common
point (their combined center of mass)
• This rotation produces a centrifugal force
• The centrifugal force just balances the
gravitational attraction between earth and the
moon
• The centrifugal force and the moon’s gravity are
not in perfect balance everywhere on earth’s
surface
• On the side nearest the moon, the moon’s gravity
is stronger and pulls the water toward the moon
• On the side away from the moon the centrifugal
force dominates and pushes the water away from
the moon
• If earth were completely covered with water, the
water would form two bulges on opposite sides of
the planet
• Water would be deep under the bulges and
shallower away from the bulges
• Earth is spinning like a top on its own axis
• As it does this any given point would be under the
bulge and then away from the bulge
• High tide occurs when a point is under a bulge
and low tide occurs when it is away from a bulge
• The earth rotates on its axis every 24 hours so a
point will have two high tides and two low tides
• The moon advances on it orbit each day so a full
tidal cycle takes 24 hours and 50 minutes
The Sun’s Bulge
• Sun produces a bulge like the moon but is it
smaller
• When the sun and the moon are in line there
bulges add up and when they are at right angle to
one another they cancel each other out
Tidal Range
• Difference in water level between successive high
and low tides
Spring Tide
• When the sun and moon bulge add together
• High high tides and low low tides
• Named because they seem to surge up like
spring water
• Occur when there is a full or new moon
Neap Tide
• Occur when sun and moon are at right angles to
one another
• Moon is in the 1st and 3rd quarters
• Average tides
• Low high tide and a high low tide
Variations in Tides
• Tides vary from place to place depending on the
location and on the shape and depth of the basin
Bay of Fundy, Canada
Tide Terms
• Semidiurnal tides – two high and two low tides
• Mixed semidiurnal tides- successive high tides of
different height
• Diurnal Tides – one high and one low uncommon
Tide Tables
• Give the predicted time and height of high and
low tides
• Very accurate
The End