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Introduction to Oceanography
Earth as a System
A system is an interacting set of components that behave in an
orderly way according to the laws of nature. One example of a system
is the human body, which consists of various subsystems including the
circulatory, digestive and respiratory systems plus energy and matter
input/output. In a healthy person, these subsystems function
internally and interact with one another in regular and predictable
ways. Based on extensive observations and understandings of a
system, scientists can predict how the system and its components are
likely to respond to changing conditions. This predictive ability is
important, for example, in dealing with the complexities of global
climate change and its potential impacts on Earth’s subsystems.
The Earth system consists of four major interacting subsystems: hydrosphere, atmosphere, geosphere and
biosphere. The photo of Earth above resembling, “a blue marble,” shows all the major subsystems of the Earth
system. (See our website for this photo in color.) The ocean, the most prominent physical feature, appears
blue; the atmosphere is made visible by swirling storm clouds off the coast of California. Land (part of the
geosphere) is mostly green because of vegetative cover (biosphere). The dominant color of Earth is blue
because the ocean covers more than two-thirds of Earth’s surface; in fact, often Earth is referred to as the
“blue planet” or “water planet.”
Hydrosphere
The hydrosphere includes water in all three phases (i.e., ice, liquid water and water vapor) that continually
cycles from one reservoir to another within Earth’s system. Water is unique among the chemical components
of the Earth system in that water is the only naturally occurring substance that co-exists in all three phases at
normal temperatures and pressures found near Earth’s surface.
The ocean, by far, is the largest
reservoir of water in the hydrosphere,
covering approximately 71% of the
planet’s surface and has an average
depth of about 3.8 km. 97% of the
hydrosphere is ocean salt water. The
next largest reservoir in the
hydrosphere is glacial ice, most of
which covers much of Antarctica and
Greenland. Ice and snow make up 2%
of water in the hydrosphere. Much
smaller quantities of water occur on
the land surface (lakes, ponds, rivers),
in the subsurface (soil moisture,
groundwater), the atmosphere (water
vapor, clouds, precipitation), and
biosphere (plants, animals).
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Ocean Basins and Plate Tectonics
The lithosphere is the rigid outer part of the planet, consisting of the crust and upper mantle. Many forces
work together to shape and reshape Earth’s lithosphere, creating and destroying both continents and ocean
basins. Forces are primarily from the movement of tectonic plates and geological processes that occur mostly
at plate boundaries. These processes produce the features on the ocean floor. Features on the ocean bottom
provide clues as to the origin of the ocean basins. Ocean depth varies markedly from one place to another.
Cross-sectional profile of continental margin and ocean bottom
Continental Margins
Based on measurements of water depth, ocean scientists delineate three distinct zones along the edges of
continents - from the coastline seaward. The zone closest to the beach features a very gentle slope extending
out to the water depth that averages about 130 m. This gently sloping zone is the continental shelf. Seaward
from the continental shelf to a depth of about 3000 m, the water depth increases much more rapidly. This
more steeply sloping zone is called the continental slope. Then a relatively narrow zone is transitional from
the steep slope of the previous zone to the more-or-less flat ocean basin. This transitional zone is called the
continental rise. The continental shelf, slope and rise together comprise the continental margin. The
bedrock of the continental margin is the same as the continental crust, predominately granite. From a
geological perspective, the continents do not end at the beach, but at the continental rise. At its outer edge, a
continental margin merges with the deep-sea floor or descends into an oceanic trench.
The continental shelf is nearly flat, sloping less than 1°. As a general rule, the shelf is narrowest where the
continental margin is tectonically active (e.g., subduction zones) and is widest where the continental margin is
passive (i.e., no plate boundary nearby). Hence, the North American shelf is much wider along the tectonically
passive East Coast (several hundreds of kilometers) than the tectonically active West Coast (a few kilometers).
About 7.5% of the total area of the ocean overlies the continental shelves.
In a passive continental margin, such as along the margin of the Atlantic Ocean, sediment accumulates over
the ocean floor forming vast, flat abyssal plains seaward of the continental rise. Along tectonically active
continental margins, the slope descends directly into deep ocean trenches.
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Submarine Canyons and Submarine Fans
Large numbers of deep, steep-sided submarine canyons slice into the continental slope and some run up onto
the continental shelf; many of these canyons cut into solid rock. A variety of mechanisms are responsible for
creating submarine canyons including erosion by turbidity currents
or ancient rivers. A turbidity current is a gravity driven flow of water
heavily laden with suspended sediment (silt, sand, and gravel)
making the water flow denser than normal seawater. Turbidity
currents can create underwater avalanches of sediment.
Eventually the pile of sediments builds to an unstable height and
suddenly slides downhill, scouring the ocean bottom in the process.
These sediments accumulate at the base of the continental rise as a
series of overlapping submarine fans. Turbidity currents have been
clocked at speeds as great as 100 km/hr.
Bathymetry of the coastal ocean showing New York’s Hudson
Submarine Canyon; this submarine canyon appears to be the
natural extension of the Hudson River.
Ocean Basins
Fringed by continental margins, ocean basins encompass the remaining portion of the oceanic area. Earth has
one ocean with many ocean basins, such as the Pacific, Atlantic, Indian, Southern and Arctic. Ocean basins
have a varied topography featuring deep trenches, seamounts, and submarine mountain ranges. Indeed,
undersea terrain is just as diverse as terrestrial terrain and exhibits an even greater relief. Over large areas
water depth is less than 200 m; in other areas the water is as deep as 11,000 m. The average ocean depth is
about 3800 m.
Mid-Ocean Ridge and
Spreading of Ocean
Basin
When adjacent plates
move apart, they
create a divergent plate
boundary. Diverging
lithospheric plates
produce rifts (fractures)
in the crust through
which magma wells up
from below. Magma
cools and solidifies
rapidly when it comes
in contact with much
colder seawater.
Through this process,
new oceanic
lithosphere is
generated at divergent
plate boundaries.
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Properties of ocean water
Hydrogen Bonding
Compared to other naturally occurring substances, water’s thermal
properties are unique. For example, based on water’s molecular weight
as well as the freezing and boiling temperatures of chemically related
substances, fresh water should freeze at about -90 °C and boil at about
-70 °C. Actually, fresh water’s freezing point is 0 °C and its boiling point is
100 °C at average sea level air pressure. Water’s
unusual properties arise from the physical structure
of the water molecule (H2O) and the bonding that occurs between water molecules.
Without this intermolecular force of attraction, known as hydrogen bonding, water would
exist only as a gas within the range of surface temperature and pressure on Earth.
Furthermore, the planet would have no water cycle, no ocean, no ice caps, and probably
no life as we know it.
Water as Ice, Liquid and Vapor
Matter exists in three basic phases: solid, liquid,
and gas. Transformations from one phase to
another always involve a large amount of energy to
alter the molecular configuration. Water readily
changes phases on Earth, contributing to the
dynamic nature of the Earth system. In changing
phase from ice to liquid to vapor, the energy state
(i.e., molecular activity) of water increases. Hence,
water molecules absorb heat energy from the
environment. In changing phase from vapor to
liquid to ice, water molecules release heat energy
to the environment. Melting, evaporation, and
sublimation are phase changes that absorb heat.
Phase changes that release heat to the surroundings are freezing, condensation, and deposition.
Sea Salts
Seawater is a salt solution of nearly uniform composition. A solution is a homogenous mixture of two or more
substances. Salinity is a measure of the amount of salt dissolved in seawater.
On average, seawater is 96.5% water and 3.5% dissolved salts. If all the ocean
water evaporated and the precipitated salts were spread evenly over the
surface of the Earth, the salts would form a layer about 45.5 m, the height of a
fifteen-story building. What is the origin of the salts dissolved in seawater? The
principal source is weathering and erosion of rock and sediment on land and
transport by rivers and streams to the ocean. As the largest reservoir in the
global water cycle, the ocean receives most of its water from rivers.
Processes operating at the atmosphere/ocean interface add or remove water
molecules from seawater and largely explain variations in sea-surface salinity.
Most dissolved substances are left behind when seawater freezes or
evaporates, increasing the surface salinity locally. On the other hand,
precipitation, runoff from rivers and melting ice add fresh water and decrease
local surface salinity. Photo shows hand harvesting of sea salt in Portugal
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Water Density and Temperature
Density is defined as mass divided by volume. When placed in water an object
that is less dense than water will float to the surface whereas an object that is
denser that water will sink. Freshwater density varies primarily with
temperature whereas seawater density varies chiefly with temperature and
salinity.
In a liquid state, cooler fresh water is denser than warmer fresh water. In a
liquid state, when comparing ocean water of the same salinity, cooler salt water
is denser that warmer salt water. In a liquid state, when comparing ocean water of the same temperature,
water with a higher salinity will be denser than water with a lower salinity.
Marine Sediments
Sediment is generated at the interfaces between the
lithosphere, atmosphere, hydrosphere and biosphere.
Physical and chemical weathering processes break down
exposed bedrock forming rock fragments (sediments) that
are transported by rivers, glaciers, wind and gravity to the
ocean. Weathering also releases soluble constituents, such
as calcium and sodium that dissolve in water and are
transported in solution to the ocean.
Image of two deltas being formed by Mississippi River
Sediments that accumulate on the sea floor differ in source, composition, size and the rate at which the
sediments accumulate on the sea floor. Of the many ways of classifying marine sediments, the two most
popular are by particle size and source of the sediment.
Size and Sorting of Sediment
Marine sediments are classified by size into three broad categories:
mud (clay and silt), sand, and gravel. Accumulations of sediment
(sediment deposits) on the seafloor also vary in the range of grain
size, known as sorting. A well-sorted sediment deposit has a narrow
range of grain sizes whereas a poorly sorted deposit has a broad
range of grain sizes. In general, the greater the distance that
sediment is transported by
running water, ocean currents,
or wind, the better sorted the
sediments become. For example
marine sediments that originated on land tend to be larger and more
poorly sorted in the continental margin than on the ocean floor.
Sources of Marine Sediment
Ocean scientists classify marine sediments based on their source as lithogenous (from rock), biogenous (from
organisms or their remains), hydrogenous (precipitated from seawater), and cosmogenous (from outer space).
Lithogenous sediment accounts for about ¾ of all marine sediments and owes its origin mostly to weathering
and erosion of pre-existing rock. Biogenous sediment includes excretions, secretions and remains of
organisms. Examples include shells, fragments of coral or skeletal parts. Biogenous sediments account for 25%
to 50% of all particles suspended in seawater.
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Marine Sedimentary Deposits
Different types of marine sediments (i.e., lithogenous, biogenous,
hydrogenous, and cosmogenous) occur in varying proportions and
thicknesses on the ocean bottom as marine sedimentary deposits.
Continental Margin Deposits
Most marine sediment deposits in the continental margin are
lithogenous and occur in a wide range of sediment sizes. Most riverborne lithogenous sediments that reach the coast do not travel very far seaward of the shoreline. About 95% of
the largest sediments transported to the ocean by rivers are trapped and deposited in bays, wetlands,
estuaries, beaches or deltas. Only about 5% of river-borne sediment brought to the shoreline reaches the
continental shelf or slope and very little sediment of terrestrial origin is transported beyond the continental
margin into the deep-ocean basins. Deposits of marine sediment are thickest on the continental margins (and
near islands) where accumulation rates are relatively high compared to deep-ocean basins. Ocean floor
sediments generally are thickest where the ocean crust is oldest so that deposits become thicker with
increasing distance from the mid-ocean ridges (divergent or spreading plate boundaries.) A notable exception
is seaward of the mouths of major sediment-transporting rivers such as the Mississippi (United States), Ganges
(Bangladesh), and Yangtse (China). Massive submarine avalanches and turbidity currents can transport
sediments hundreds or thousands of kilometers out onto the continental rise and to the sea floor beyond.
Deep-Ocean Deposits
Fine-grained sediments that gradually accumulate particle-by-particle on the deep-ocean floor are mostly
biogenous and their accumulation rates are considerably slower than continental-margin deposits. On average,
a 1 mm-thick layer forms in about 1000 years. (A 1-inch thick layer forms in about 25,000 to 250,000 years.)
Marine Sedimentary Rock
As part of the rock cycle, over the millions of years that
constitute geologic time, sediment that is deposited on
the ocean floor is gradually converted to solid marine
sedimentary rock through lithification. Lithification usually
involves both compaction and cementing of sediments.
Sediments are compacted by the increasing weight of
sediments accumulating above that squeeze deeper
sediments closer together. Siliceous and calcareous fluids
migrating through the tiny openings between individual
sediment grains precipitates minerals that fill the pore
spaces, cementing grains to one another. The product of
lithification is sedimentary rock such as shale, sandstone,
or limestone depending on the composition and particle
size of the constituent sediments. With deeper burial and
further increases in temperature, pressure, and access to
chemically active fluids, sedimentary rock may be
converted to metamorphic rock such as slate, schist or
gneiss.
Marine Sedimentary strata found in the interior of North America is evidence of an extensive shallow sea,
the Western Interior Seaway during the mid-Cretaceous, about 100 million years before the present
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The atmosphere and the ocean
What role does the ocean play in the long-term average state of the atmosphere? The ocean plays a key role in
the global radiation budget, the transport of heat between Earth’s surface and atmosphere; the flow of heat
from the tropics to the higher latitudes, and the development of storm systems.
Weather and Climate
Weather and climate are closely related concepts. Weather is the state of
the atmosphere at some place and time described in terms of such
variables as temperature, precipitations, cloud cover, and wind speed. A
place and time must be specified when describing weather because the
atmosphere is dynamic; that is, its state is always changing from one place
to another and with time. From personal experience, we know that
tomorrow’s weather may differ considerably from today’s weather.
Climate is defined as weather at a particular place averaged over a
specified interval of time. By international convention, average values of
weather elements, such as temperature, precipitation, are computed over
a 30-year period. Other useful climate parameters include average seasonal snowfall, length of growing season,
and frequency of thunderstorms. Ultimately, climate governs the supply of fresh water, the geographical
distribution of plants and animals and the types of crops that can be cultivated.
Heating and Cooling Earth’s Surface
As the Earth orbits the sun, its atmosphere and the surface are absorbing energy radiated by the sun. This
energy, when absorbed, is called heat energy. Absorption of solar radiation heats the Earth-atmosphere
system. At the same time the entire Earth-atmosphere system is emitting infrared radiation to space, which
has a cooling effect on the Earth-atmosphere system. Over the long term, radiational cooling of the planet
essentially balances radiational heating of the planet so that Earth remains in radiative equilibrium with
surrounding space.
Solar Radiation Budget
Solar radiation intercepted by Earth travels through the atmosphere
Average Albedo of some common
and interacts with its component gases and aerosols, minute solid
surface types
and liquid particles which are suspended in the atmosphere. These
Surface
Albedo (% reflected)
interactions consist of scattering, reflection and absorption. Solar
Forest
7-18%
radiation that is not absorbed or scattered or reflected back to space
Tundra
15-35%
reaches Earth’s surface where additional interactions occur. With
Desert
25-30%
scattering, a particle disperses radiation in all directions: up, down,
Urban Area
14-18%
and sideways. Within the atmosphere, both gas molecules and
Crops
15-25%
aerosols scatter solar radiation. Reflection is a special case of
Water
10-100%
scattering in which a large surface area redirects the radiation in a
Fresh snow
75-95%
backward direction. The fraction of incoming radiation that is
Old snow
40-60%
reflected by a surface is known as the albedo of that surface.
Cirrus Clouds
40-50%
Surfaces having a high albedo, such as glaciers, reflect a relatively
Soil
5-30%
large fraction of incoming solar radiation and appear light in color.
Surfaces having a low albedo, such as the ocean, reflect relatively little incoming solar radiation and appear
dark in color.
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Scattering and reflection within the atmosphere alter the direction of solar radiation without converting the
radiation to heat. Absorption, however, is the process whereby some of the radiation that strikes an object is
converted to heat energy. Oxygen, ozone, water vapor, and some aerosols absorb radiation in the atmosphere.
Solar radiation not scattered to space or absorbed by atmospheric gases or aerosols reaches Earth’s surface
where it is either reflected or absorbed. The portion that is not reflected is absorbed (i.e., converted to heat).
High-albedo surfaces, such as snow-covered ground or pack ice, reflect a considerable amount of incoming
solar radiation whereas low-albedo surfaces, such as an asphalt parking lot or a forest, reflect much less
incoming solar radiation. (See the table on page 7 for the albedo of some common surfaces.)
Measurements by sensors onboard
Earth orbiting satellites indicate that
the Earth-atmosphere system reflects
or scatters back to space on average
about 31% of the incoming solar
radiation intercepted by the planet.
This is Earth’s planetary albedo. The
atmosphere (i.e., gases, aerosols,
clouds) absorbs only about 20% of the
total solar radiation intercepted by the
Earth-atmosphere system. In other
words, the atmosphere is relatively
transparent to solar radiation. The
remaining 49% of solar radiation is
absorbed by Earth’s surface, mostly by
the ocean.
Earth’s surface is the principal recipient
of solar heating, and heat is transferred from Earth’s surface to the atmosphere, which eventually radiates this
energy to space. Hence, Earth’s surface is the main source of heat for the atmosphere; that is, the atmosphere
is heated from below. This is evident from the average vertical temperature profile of the troposphere, the
lowest layer of the atmosphere; where the atmosphere interfaces with the ocean, lithosphere, and biosphere
and where most weather takes place.
Solar Radiation and the Ocean
Whereas the atmosphere is relatively transparent to (and absorbs
little) solar radiation, the ocean absorbs most solar radiation
within relatively shallow depths. The photic zone is the sunlit
surface layer of the ocean, down to the depth where light is just
sufficient for photosynthesis. With some notable exceptions,
marine life depends directly or indirectly on sunlight and organic
productively in the ocean’s photic zone. Even the diverse
community of animals living at great depths on the ocean floor
depends on organic particles produced within the photic zone
that settle to the sea floor; exceptions are organisms living near
hydrothermal vents.
Close up view of giant tubeworms living near hydrothermal vent
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Infrared Radiation and the Greenhouse Effect
If solar radiation were continually absorbed by the Earth-atmosphere system without any compensating flow
of heat out of the system, Earth’s surface temperature would rise steadily. Eventually, life would be
extinguished and the ocean would boil away. Actually, global air temperature changes very little from one year
to the next. Global radiative equilibrium keeps the planet’s temperature in check to some extent; that is,
emission of heat to space in the form of infrared radiation balances solar radiational heating of the Earthatmosphere system. Although solar radiation is supplied only to the illuminated half of the planet, infrared
radiation is emitted to space ceaselessly, day and night, by the entire Earth-atmosphere system. This explains
why nights are usually colder than days and why air temperatures typically drop throughout the night.
While the clear atmosphere is relatively transparent to solar radiation, certain gases in the atmosphere impede
the escape of infrared radiation to space thereby elevating the temperature of the lower atmosphere. This
important climate control, the so-called greenhouse effect, refers to the heating of Earth’s surface and lower
atmosphere caused by strong absorption and emission of infrared radiation (IR) by certain gaseous
components of the atmosphere, known as greenhouse gases. Water vapor is the principal greenhouse gas.
Other greenhouse gases include carbon dioxide (CO2), ozone (O3), and methane (CH4). Solar radiation and
infrared radiation have different properties and interact differently with the atmosphere. As noted earlier, the
atmosphere absorbs only about 20% of the solar radiation intercepted by the planet. However, the
atmosphere absorbs a greater percentage of the infrared radiation emitted by Earth’s surface, and the
atmosphere, in turn, radiates some IR to space and some back to Earth’s surface. Hence, Earth’s surface is
heated by absorption of both solar radiation and atmosphere-emitted infrared radiation.
Arizona Dessert in Southwestern U.S.
Florida Everglades just off the Gulf Coast
Warming caused by atmospheric water vapor is evident even at the local or regional scale. Consider an
example. Locations in the Desert Southwest and along the Gulf Coast are at about the same latitude and on a
clear day receive essentially the same input of solar radiation. In both places, summer afternoon high
temperatures commonly read 32 °C. At night, however, air temperatures often differ markedly. Air is relatively
dry (low humidity) in the Southwest so that infrared radiation readily escapes to space and air temperatures
near Earth’s surface may drop well under 15 °C by dawn. People who camp in the desert are well aware of the
dramatic fluctuations in temperature between day and night. Infrared radiation does not escape to space as
readily through the Gulf Coast atmosphere where the air is more humid. Water vapor strongly absorbs IR and
emits IR back towards Earth’s surface so that early morning low temperatures may dip no lower than the 20s
Celsius. The smaller day-to-night temperature contrast along the Gulf Coast is due to more water vapor and a
stronger greenhouse effect.
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Latent Heating and the Exchange
of Heat Energy from the Ocean
to the Atmosphere
Latent heating refers to the
transfer of heat energy from one
place to another as a
consequence of phase changes of
water. When water changes
phase, heat energy is either
absorbed from the environment
(i.e., melting, evaporation,
sublimation) or released to the
environment (i.e., freezing,
condensation, deposition). As
part of the global water cycle,
latent heat that is used to
vaporize water at the Earth’s
surface is transferred to the atmosphere when clouds form. Significantly for Earth’s climate, ocean water
covers a large portion of Earth’s surface and is the principal source of water vapor that eventually returns to
Earth’s surface as precipitation. In general, only well inland does most precipitations originate as evaporation
from the continents. Also, the ocean is a major source of salt crystals that spur condensation and cloud
development in the atmosphere.
As Earth’s surface absorbs radiation (both solar
and infrared), some of the heat energy is used to
vaporize water from oceans, glaciers, lakes,
rivers, soil and vegetation. The latent heat
required is supplied at the Earth’s surface, and
heat is subsequently released to the atmosphere
during cloud development. During cloud
formation, water changes phase - water vapor
condenses into liquid water or deposits as ice
crystals - and latent heat is released to the
atmosphere. Through latent heating, then, heat
is transferred from Earth’s surface to the
troposphere. In fact, latent heat transfer is more
important than either radiational cooling or
sensible heat transfer (conduction and
convection) in the cooling of Earth’s surface.
Acquisition and subsequent release of latent heat in storm systems play an important role in the poleward
transport of heat. At low latitudes, near the equator, water that evaporates form the warm ocean surface may
be drawn into a developing storm system. As the storm travels into higher latitudes, some of that water vapor
condenses into clouds, thereby releasing latent heat to the troposphere.
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Map of major wind surface currents on Earth
Heat Transport by Ocean Circulation
The ocean contributes to poleward heat transport via wind-driven surface currents and the deeper
thermohaline circulation. Surface water that is warmer than the overlying air is a heat source for the
atmosphere; that is, heat is conducted from sea to air. Surface water that is cooler than the overlying air is a
heat sink for the atmosphere; that is, heat is conducted from the air to the sea. Warm surface currents, such as
the Gulf Stream, flow from the tropics into middle latitudes, supplying heat to the cooler middle latitude
troposphere. At the same time, cold surface currents, such as the California Current, flow from high to low
latitudes, absorbing heat from the relatively warm troposphere and greater solar radiation in the tropics.
The ocean’s thermohaline circulation
is the density-driven movement of
water masses, traversing the lengths
of ocean basins. The density of
seawater increases with decreasing
temperature and increasing salinity.
More dense water tends to sink while
less dense water rises. The
thermohaline circulation transports
heat energy, salt and dissolved gases
over great distances and to great
depths in the World Ocean and plays
and important role in Earth’s climate
system.
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Moving Water
Energy and matter (e.g., heat, water) are continually exchanged between the ocean and atmosphere, and
theses processes drive the ocean circulation. Evaporation, precipitation, runoff from the continents plus
heating and cooling bring about changes in the temperature and salinity of surface waters. Density changes
that accompany variations in temperature and salinity can cause water to sink or rise in the ocean. Kinetic
energy is transferred from near-surface winds to the ocean’s surface layer, driving the currents that dominate
the motion of the ocean’s surface, the upper hundred meters or so.
Most seawater (90%) is in the deep ocean, isolated from the atmosphere and its winds. Deep ocean waters are
cold and dark and come to the surface primarily at high latitudes where they interact with the atmosphere.
Differences in water density drive the sluggish circulation of deep water. Typically these waters flow at speeds
of less than 1 km per day – about 240 times slower than the Gulf Stream.
Wind Driven Surface Currents
Wind driven surface currents in the
surface layer are maintained by
kinetic energy transferred from the
horizontal winds to ocean surface
waters. Once the wind sets surface
waters in motion as a current, the
Coriolis Effect and the shape of the
ocean basin modify the speed and
direction of these surface currents.
The Coriolis Effect is a force due to
Earth’s rotation that causes
deflection of moving objects to the right in the Northern Hemisphere and the left in the Southern Hemisphere.
Density Driven Thermohaline
The upper portion of the ocean is put into motion by wind forcing at the surface. Below the upper 100 meters,
the deep ocean is shielded from the direct action of the wind and ocean currents are driven primarily by
density differences in the water masses. These
density contrasts are caused by variations in water
temperature and salinity with cold salty water being
the densest combination. The deep-ocean circulation
driven by variations in density is called the
thermohaline circulation, the name coming from
thermo meaning heat and haline referring to salinity.
Another name for this circulation system is the
meridional overturning circulation (MOC) because
this is the primary mode of water motion (sinking at
high latitudes and upwelling at low latitudes).
Upwelling refers to the upward circulation of cold,
nutrient-rich bottom water toward the ocean
surface. Downwelling refers to the downward
motion of surface waters.
Schematic of upwelling
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Waves
Kinetic energy (energy of motion) of air in motion (the wind) is transferred to the
ocean surface causing surface waves. Wind-driven ocean waves are oscillations,
regular fluctuations, of the sea surface that move horizontally along the
ocean/atmosphere interface away from where the waves were generated.
Energy is propagated with the wave – not the water. Wave height, depends on
wind speed, duration of the wind in the same direction, and the distance over
which the wind blows.
Ocean Tides
Astronomical tides are the regular rise and fall of the sea surface
caused by the gravitational attraction between the rotating Earth
and the moon and the sun. The tide generating force is produced
by the combination of (1) the gravitational attraction between the
Earth and the moon and sun, and (2) the rotations of the Earthmoon system and the Earth-sun system. Forces combine to deform
Earth’s ocean surface into a roughly egg –shape with two bulges.
One ocean bulge faces towards the moon and the other is on the
opposing side of the planet, facing away from the moon. A similar
interaction between the Earth and sun produces two other ocean
bulges that line up towards and away from the sun. The ocean
tidal bulges produced by the moon remain in the same alignment
relative to the moon, as well as the ocean tidal bulges produced by
the sun remain in the same alignment relative to the sun. Its
Earth’s daily 24 hour rotation underneath these tidal bulges that
allows us to experience low and high tides.
Schematic of gravitational forces causing tides
According to the law of universal gravitation, the greater the
mass, the greater the force of attraction whereas the greater
the distance, the smaller the force of attraction. Although the
sun is 107 times more massive than the moon, the moon is
much closer to Earth and for that reason exerts a greater
gravitational pull on Earth. Tides typically are measured at
coastal locations as local changes are sea level as a function of
time. The difference in height between water levels at high and
low times is called the tidal range and the time between
successive high tides is the tidal period.
Newton’s first law of motion, an object in constant straight line
motion remains in that motion unless acted upon by an
unbalanced force. In a rotating system, such as the Earth-moon
system, the net force confines an object to a curved path (rather than a straight) path. Consider an analogy.
Suppose that you are a passenger in an auto that rounds a curve at high rate of speed. You feel a force that
pushes you outward from the turning auto. Actually, you are experiencing the tendency for our body to
continue moving in a straight path while the auto follows a curved path. In the same way, the rotation of the
Earth-moon system causes the ocean to bulge outward on the side of the planet opposite the moon.
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Marine Ecosystems and Life in the ocean
The ocean is home to a huge number of different types of
species or organisms-perhaps as many as 10 million-and
many more are yet to be discovered and studied. The
wide variety of marine habitats makes possible this great
biodiversity. Some marine ecosystems, such as coral
reefs, are structurally complex and provide niches for
many types of organisms that have evolved different
adaptations to their environment. The discovery of
hydrothermal vents and their associated thousands of
species of marine organism dates only to 1979.
Many of the fundamental requirements for life in the
ocean are the same as those needed by terrestrial
organisms. Essential for life on Earth are a source of
energy (e.g., sunlight), liquid water, the appropriate mix
of chemical constituents (e.g., nutrients) and the right
combination of environmental conditions (e.g., range of
temperature). One major difference between life in the
ocean and life on land is the much greater space and variety of marine habitats.
All living organisms require energy, which they obtain either as producers (via photosynthesis or
chemosysthesis) or as consumers eating other organisms. Photosynthetic organisms in the ocean, such as
plants, algae and some bacteria, use light energy (solar radiation) to convert simple inorganic compounds
(carbon dioxide and water) into complex energy-rich organic substances, which provide energy to consumers
that eat these photosynthetic organisms. Decomposers are consumers that feed on dead organic matter,
either on the ocean bottom or within the water. Decomposers are essential components of all ecosystems
because they break down organic matter and recycle nutrients back into the ecosystem.
Food webs, such as above, show the sequences of feeding relationships among organisms (e.g., producers,
consumers, decomposers) through which energy and materials move within an ecosystem. Within food chains
and food webs, energy transfer occurs in one direction, from the lower feeding levels (producers) to the
higher feeding levels (consumers). Each feeding position
occupied by an organism within a food web is called a
trophic level. In the food web above, the organisms in the
lowest trophic level are dinoflagellates and diatoms, while
the organisms on the highest trophic level are the large
sharks. Food webs are pathways not only for energy but also
for toxins, that is, poisons that persist in the environment
because they do not break down physically, chemically, or
biologically.
Marine life is commonly defined in terms of distance from
shore and water depth. The open ocean constitutes the
pelagic zone, home to passive floaters, weak swimmers and
strong swimmers. The environment of the sea floor at all depths is called the benthic zone, home to organisms
that live either on the ocean bottom or within sediment deposits.
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Review Questions
1) Describe the subsystem on Earth called the Hydrosphere.
2) Identify the second largest reservoir in the hydrosphere and its location.
3) Describe the general relationship between continental shelf width and tectonic activity in the continental margin.
4) Describe the unique properties of the water molecules mentioned in the reading.
5) Identify and describe the three phase changes of water during which heat energy is released to the environment.
6) Identify and describe the three phase changes of water during which heat energy is absorbed from the environment.
7) Describe what processes decrease sea-surface salinity of ocean water.
8) Describe what processes increase sea-surface salinity of ocean water.
9) Compare the salinity of surface ocean waters in regions where the precipitation is low but evaporation rates are high
to the salinity of surface ocean waters in regions where the precipitation is high but evaporation rates are low.
10) At a constant temperature, how does the density of seawater change with increasing salinity? With constant salinity,
how does the density of seawater change with falling temperatures?
11) What are the four major groups of marine sediments? Briefly describe the source of each sediment type.
12) Compare continental-margin deposits to deep-ocean deposits.
13) Describe the difference between weather and climate.
14) Describe what happens to solar radiation during scattering, reflection and absorption.
15) Give an example of how the albedo of a specific surface type will impact the solar radiation budget of the Earthatmosphere system.
16) What is the major source of heat energy for the troposphere, the lower atmosphere?
17) Using one of the maps of the wind surface currents on Earth, compare the rotation direction of surface currents in
the Northern Hemisphere to the rotation direction of surface currents in the Southern Hemisphere.
18) Describe the thermohaline circulation system and what is causing this circulation system.
19) What major forces cause the tides?
20) Describe what does a food web shows.
Guide to reading textbook:
Overview of Reading (due Wednesday, Feb. 29)
1) Read over the Review Questions, usually at the end of the reading.
2) Skimming. Skim the chapter quickly, noticing headlines, pictures and graphs. This takes just a few minutes. You are
not trying to understand the chapter yet, but just getting the general topic being covered
Tackling Vocabulary (due Friday, March 2)
3) Read the article in its entirety. As you are reading the article, circle any words that you do not know.
4) Go back and find the words that you have circled and read the entire sentence that contains this word.
5) Do you recognize any parts of this word, what parts of this word do you recognize? In the margins jot down what each
word could mean using clues from the reading. If you still don’t have any idea…look up the term in a dictionary.
Understanding the Reading (due Monday, March 5)
6) Go back and read the whole chapter, section by section, for comprehension. Next to each paragraph or on a separate
piece of paper, write one or two sentences that summarize the ideas in that paragraph, draw images that are described
and write down any questions you have after reading that paragraph.
Practice your Understanding (due Wednesday, March 7)
7) After you understand the chapter and each paragraph, answer the Review Questions.
Remaining Questions (due Wednesday, March 7)
8) Follow up with Teacher. Utilize your teachers extra help days to ask for clarification. Think of it as Mrs. Ciarametaro’s
and Ms. Schofield’s office hours .
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