Download Earth as a system - David M. Lawrence

MAR 110: Introductory
Oceanography
Earth in the ocean system
Mars and the solar system, part 1
• Mars has long been thought of having liquid water,
but now much of the surface of the planet is an arid
wasteland.
• There is evidence that liquid water once flowed over
the surface of Mars, and there is liquid water in the
planet’s polar ice caps, but the planet’s thin
atmosphere and extremely cold temperatures (ranging
from -60 °C at the equator to -123 °C at the poles)
ensures that what water is at the surface is in the form
of ice.
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Mars and the solar system, part 2
• Liquid water does appear to be a major component of
the surface of some solar system objects, such as
three moons of Jupiter: Europa, Ganymede, and
Callisto.
– Actually, the moons are frozen at the surface, with water
(kept liquid as a result of frictional heating generated by
strong tides created by Jupiter’s gravity) beneath the frozen
surface.
• Nevertheless, the Earth is the true water planet.
– Most of that water lies in the Earth’s oceans.
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Earth as a system
• A system is an interacting set of components that
behave in an orderly way according to the laws of
physics, chemistry, geology, and biology.
• As scientists gain a better understanding of how a
system works, they can better predict how the system
and its components will respond to changing
conditions.
• The Earth system consists of four environmental
spheres.
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Environmental spheres
• Earth’s surface is a complex interface where four
spheres meet, overlap, and interact. These spheres
provide important organizing concepts for the
systematic study of the geosciences:
–
–
–
–
Geosphere (the solid, inorganic portion)
Atmosphere (the gaseous envelope that surrounds Earth)
Hydrosphere (water in all its forms)
Biosphere (life and the places where it can exist)
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The hydrosphere, part 1
• The hydrosphere includes water in all three states of
matter: solid, liquid, and gas.
– Water is unusual in that it occurs in all three states of matter
under normal conditions at the Earth’s surface.
• Compartments of the hydrosphere
– The largest reservoir of water on Earth is the oceans, which
cover 70.8 percent of the Earth’s surface, with an average
depth of 3.8 km – but the oceans make up only 0.02 percent
of the Earth’s mass.
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The hydrosphere, part 2
• Compartments of the hydrosphere (continued):
– The second largest reservoir in the hydrosphere is glacial
ice, with the Antarctic and Greenland ice packs the largest
and second largest expanses of ice, respectively.
– Other reservoirs include land surface waters (lakes, rivers,
etc.), subsurface waters (soil moisture and groundwater),
the atmosphere (water vapor, clouds, and precipitation),
and the biosphere (water in living organisms).
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The hydrosphere, part 3
• The hydrosphere is dynamic, with exchanges of water
taking place within and between the reservoirs
constantly.
– The oceans are the ultimate destination of water, however.
• The oceans and atmosphere are tightly coupled.
– Wind drives ocean currents.
• Wind-driven currents are limited to about 100 m in depth and take
several months to cross an ocean basin.
• Deep-ocean currents are more sluggish and typically have little to
do with wind, being driven by differences in water density
produced by small differences in temperature and salinity.
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The hydrosphere, part 4
• Ocean-atmosphere coupling (continued):
– Ocean currents (continued):
• The densest ocean waters form in polar and subpolar regions where
salt, which is excluded from forming ice crystals, gets concentrated
in the remaining water; additional cooling increases density.
• As dense ocean waters form in polar and subpolar regions, they
sink and flow along the bottom of the oceans, thus forming deep
currents that become part of the ocean conveyor belt system.
• The deep waters eventually diffuse to the surface and mix with
surrounding waters, thus diluting the salinity.
• Heating and evaporation from the surface, however, increases the
salinity and the hot, salty waters are transported back toward the
poles, thus completing the conveyor belt system.
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The hydrosphere, part 5
• The frozen portion of the hydrosphere is called the
cryosphere.
– The cryosphere consists of glacial ice sheets, alpine
glaciers, permafrost, pack ice, and ice bergs.
• A glacier is a mass of that flows internally under tremendous
pressure.
– Glacial ice sheets, averaging about 3 km, cover most of
Antarctica and Greenland.
• Antarctica contains 90 percent of the planet’s ice.
– Glacial ice cover about 10 percent of the Earth’s surface at
present.
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The hydrosphere, part 6
• The cryosphere (continued):
– Glaciers form where snowfall exceeds snowmelt.
• As snow accumulates, pressure of the overlying snow compacts
snowflakes below into ice crystals; they may also trap gas bubbles
recording the characteristics of the atmosphere at the time the snow
fell.
• The pressure of the overlying snow and ice triggers flow of the ice
mass down hill; the pressure is so great that the solid mass of ice
flows like a fluid.
– Glaciers expand and contract with changes in climate.
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The hydrosphere, part 7
• The cryosphere (continued):
– In some areas, such as Antarctica, Greenland, and Alaska,
glaciers flow out into the sea.
• Antarctic ice forms large ice shelves.
• Portions of these ice shelves and glaciers can break off, forming ice
bergs such as the one that led to the demise of the RMS Titanic.
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The atmosphere, part 1
• The atmosphere is the thin layer of gases and
suspended particles that surrounds the Earth; it
extends into pore spaces in soils, caves, and mines.
– The atmosphere accounts for only about 0.07 percent of the
mass of the Earth.
• The atmosphere is essential for life.
• Unlike water, air is compressible.
– Half of the atmosphere’s mass is concentrated within 5,500
m of the the Earth’s surface; 99 percent of the mass is
concentrated within 32 km of the surface.
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The atmosphere, part 2
• The atmosphere merges with interplanetary gases
about 1,000 km above the surface.
• The atmosphere is layered, with the primary layers
defined by thermal characteristics.
– The troposphere is the lowest layer; temperature decreases
with altitude in the troposphere.
• The troposphere is the portion of the atmosphere that interacts with
the hydrosphere, lithosphere, and biosphere.
• Weather occurs in the troposphere.
• The troposphere contains 75 percent of the atmosphere’s mass and
99 percent of its water.
• Above the troposphere lies a transitional zone, the tropopause.
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The atmosphere, part 3
• Atmospheric layers (continued):
– Above the tropopause is the stratosphere, about 10 to 50
km above the Earth’s surface; temperature increases with
altitude in the stratosphere.
• The stratospheric ozone layer protects life from the ultraviolet
layers of the sun.
• Above the stratosphere lies a transitional zone, the stratopause.
– Above the stratopause is the mesosphere, up to about 80
km above the surface; temperature decreases with elevation
in the mesosphere.
• Above the mesosphere lies a transitional zone, the mesopause.
• The atmosphere is a mixture of gases.
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The atmosphere, part 4
• Atmospheric layers (continued):
– Above the mesopause is the thermosphere; temperature
increases with elevation in the thermosphere.
• Above the mesosphere lies a transitional zone, the mesopause.
• The atmosphere is a mixture of gases.
– Nitrogen (N2) is the most abundant, making up 78 percent
of the atmosphere.
– Oxygen (O2) is second most abundant, making up 21
percent of the atmosphere.
– The concentration of water vapor (H2O), is variable both
spatially and temporally.
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The atmosphere, part 5
• The atmosphere also contains suspended particles
called aerosols.
– The sources of aerosols include: soil particles, ocean spray,
wildfires, volcanic eruptions, smokestacks and chimneys,
vehicle exhaust.
– Aerosols serve as condensation nuclei; condensation nuclei
are necessary for raindrop formation.
– Aerosols may reduce global warming by blocking some of
the radiation from the sun; they may contribute to warming,
however, at nighttime by radiating heat absorbed during the
day.
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The atmosphere, part 6
• Atmospheric water vapor is essential for life and is a
major driver of the hydrologic cycle as well as
weather and climate even though it never makes up
more than 4 percent (by volume) of the atmosphere.
• Carbon dioxide (CO2) makes up only 0.037 percent
of the atmosphere, but is essential for life on Earth as
it is one of the raw materials of photosynthesis.
• Ozone (O3) between 30 and 50 km in altitude shields
life on Earth from ultraviolet radiation.
– It is considered a pollutant at the surface, however.
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The atmosphere, part 7
• The atmosphere is constantly in motion; much of the
motion redistributes solar energy from the tropics,
where energy is at a surplus; to the poles, where
energy is at a deficit.
– The motion is driven by temperature gradients from one
region to another.
– The oceans contribute to this heat transfer.
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The geosphere, part 1
• The geosphere is the solid portion of the planet,
consisting of rocks, minerals, and sediments.
• Much of the geosphere cannot be observed directly.
– The deepest mining and drilling projects reach to only
about 12 km below the surface.
– Most of what we know about the interior of the Earth
comes from study of seismic (sound) waves that pass
through it.
– Meteorites provide clues to the history and composition of
the early Earth.
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The geosphere, part 2
• The Earth has a number of layers.
– The crust is the outer, solid skin, ranging in thickness from
8 km under oceans to 70 km in continental mountain belts.
– Beneath the crust is the mantle, a rigid but fluid layer about
2,900 km thick.
• The crust and outer portion of the mantle comprise the lithosphere
proper.
– Next is the molten outer core, which surrounds the solid
inner core.
• The inner core is solid, but because of high temperatures and
pressures, behaves as a fluid.
• The combined radius of the inner and outer core is about 3,500 km.
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The geosphere, part 3
• Relief is the difference between the highest and
lowest portions of the landscape.
• Internal versus external processes
– Internal processes lift up the land surface through tectonic
activity, creating landforms that increase relief.
• Internal processes include volcanism and other forms of mountain
building.
– External processes reduce relief by wearing down high
places and filling in low places.
• External processes include weathering and erosion.
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The geosphere, part 4
• Plate tectonics explains the structure of the surface of
the Earth, including all volcanic activity and most
earthquake activity.
– The Earth’s crust is divided into 12 major plates and a
number of minor plates that are driven across the surface
by convection currents in the mantle.
– The plates split apart, collide, and slide past each other,
creating and destroying landforms in a process that has
probably gone on for several billion years.
• Pangaea was a supercontinent made up of the other major land
masses that broke up about 200 million years ago.
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The geosphere, part 5
• Magma, hot molten rock, often wells up into fissures
in the crust where it is splitting apart, or up through
overlying rock in areas where crustal plates collide.
– Magma also wells up at hot spots, where a crustal plate
drifts over a deep plume of rising magma.
• The Hawaiian Islands and Emperor Seamount Chain in the Pacific
were created as the Pacific Plate drifted over a hot spot.
• Weathering is the physical disintegration, chemical
decomposition, or solution of exposed rock.
– Weathering creates sediments, which in turn can be
modified to form soil.
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The geosphere, part 6
• Soil is the thin interface between the atmosphere and
geosphere
– Soil = ƒ(cl,o,r,p,t)
• Soil characteristics are a function of climate, organisms, parent
material (underlying rock), relief (terrain), and time.
– Soil characteristics influence nutrient availability.
• Poor soils are not suitable for agriculture without modification.
• Human activities can degrade soils and lead to soil loss via erosion.
• Erosion is the removal and transport of sediments and
soil by gravity, water, glaciers, and wind.
– Sediments are deposited in low-lying basins.
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The geosphere, part 5
• Magma, hot molten rock, often wells up into fissures
in the crust where it is splitting apart, or up through
overlying rock in areas where crustal plates collide.
– Magma also wells up at hot spots, where a crustal plate
drifts over a deep plume of rising magma.
• The Hawaiian Islands and Emperor Seamount Chain in the Pacific
were created as the Pacific Plate drifted over a hot spot.
• Weathering is the physical disintegration, chemical
decomposition, or solution of exposed rock.
– Weathering creates sediments, which in turn can be
modified to form soil.
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The biosphere, part 1
• The biosphere consists of all the living organisms on
Earth.
– Living organisms range in size from the smallest bacteria to
the largest plants (redwoods) and animals (blue whales).
– Despite their small size, bacteria and other single-celled
organisms dominate the biosphere.
• Organisms on land or above the surface live relatively
close to the surface, whereas marine organisms live
throughout the oceans’ depths.
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The biosphere, part 2
• Most of life on Earth is tied to the other Earth
subsystems via photosynthesis and cellular
respiration.
– Photosynthesis is the process by which plants harvest light
energy from the Sun and use it to power the assembly of
sugars (CH2O) from carbon dioxide (CO2) and water
(H2O).
– Cellular respiration is the process by which organisms
harvest energy stored in sugars and other organic
compounds.
• Respiration requires oxygen (O2) and produces CO2 and H2O.
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The biosphere, part 3
• Organisms interact with each other as well as with
their physical and chemical environment in
ecosystems.
– An ecosystem consists of the biotic and abiotic components
of the environment in a particular location.
– Ecosystems can be described in terms of trophic levels,
which are levels in a hierarchy of feeding relationships.
• The basic level is the producer level, photosynthetic or
chemosynthetic organisms upon which all other levels – of
consumers – ultimately depend.
– Herbivores feed on the producers.
– Carnivores feed on herbivores as well as other carnivores.
– Decomposers feed on everything.
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The biosphere, part 4
• Organism interactions (continued):
– Feeding relationships can be described in terms of food
chains, which are linear depictions of feeding relationships
going from producers to top consumer; or they can be
described (more realistically) in terms of food webs, with
interactions within levels as well as across multiple levels.
• Estuaries are especially important type of ecosystems
in the coastal zones.
• Freshwater life and marine life meet and mix in estuaries.
• The Chesapeake Bay, San Francisco Bay, and Puget Sound are
among the most important estuaries in the United States.
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The biosphere, part 5
• Energy is the capacity to do work.
• There are two types of energy.
– Kinetic energy is the energy of motion.
• Heat (thermal) energy is kinetic energy associated with the random
movement of atoms or molecules.
– Potential energy is the energy possessed by matter as a
result of location or structure.
• Chemical energy is potential energy available for release in a
chemical reaction.
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The biosphere, part 6
• Thermodynamics is the study of energy
transformations.
• There are two types of thermodynamic systems.
– Closed systems do not exchange matter and/or energy with
their surroundings.
– Open systems do exchange matter and/or energy with their
surroundings.
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The biosphere, part 7
• The first law of thermodynamics states that energy
can be transferred and transformed, but never created
nor destroyed.
• The second law of thermodynamics states that every
energy transfer or transformation leads from more
order to more disorder in the universe.
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Biogeochemical cycles, part 1
• Biogeochemical cycles are cycles of energy and
nutrients though the biosphere, atmosphere,
geosphere, and hydrosphere.
• Some of the major biogeochemical cycles include:
–
–
–
–
–
Water
Carbon
Nitrogen
Oxygen
Phosphorus
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Biogeochemical cycles, part 2
• For any given reservoir in a biogeochemical cycle,
– Input = Output + Storage
• Cycling rate is the amount of material that moves
from one reservoir to another within a period of time.
• Residence time is the amount of time it takes for a
substance in a reservoir to be completely replaced.
– The residence time of water ranges from about 10 days in
the atmosphere to tens of thousands of years in glacial ice.
– Residence times for dissolved substances in seawater range
from 100 years for aluminum to 260 million years for
sodium.
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Biogeochemical cycles, part 3
• The carbon cycle
– Photosynthesis takes inorganic carbon (CO2) from the
atmosphere and converts it to organic carbon (CH20).
• The sugars are converted into other compounds, such as other
carbohydrates, lipids, proteins, and nucleic acids.
– Organisms convert some of that organic carbon back into
CO2.
– In the oceans, some CO2 is dissolved in the water.
• Marine organisms use that carbon, in the form of CaCO3, to make
their shells.
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Biogeochemical cycles, part 4
• The carbon cycle (continued):
– As marine organisms die, their bodies sink to the bottom.
• The shells are buried under sediments, and under great pressure. In
time, these deposits are converted to rocks such as limestone and
dolostone.
• These rocks may be eventually uplifted and exposed to weathering
and erosion.
– CO2 dissolved in water vapor (H2O) in the atmosphere forms carbonic
acid (H2CO3), which contributes to the weathering of carbonate rocks.
• During the Carboniferous Period, from 280 million to 345 million
years ago, trillions of metric tons of organic material was deposited
in oceans and swamps, eventually giving rise to the coal and
petroleum deposits upon which we depend for energy.
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Biogeochemical cycles, part 5
• The hydrologic cycle
– The hydrologic cycle is also called water cycle; It describes
the movement of water among the hydrosphere,
atmosphere, lithosphere, and biosphere.
– Water is also an important means of transport of materials
in other biogeochemical cycles.
– Water is present in more or less constant amounts, being
emitted by volcanic activity or deposited via meteorites; but
it is also consumed in chemical reactions and destroyed via
photodissociation.
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Biogeochemical cycles, part 6
• The hydrologic cycle (continued):
– Water enters the atmosphere via:
• Evaporation, in which liquid water is converted to water vapor;
• Transpiration, loss of water through the leaves of plants; and
• Sublimation, in which ice is converted to water vapor.
– Water enters the oceans via:
• Surface and groundwater runoff;
• Precipitation; and
• Melting of ice and runoff of meltwater.
– Water enters the land via:
• Precipitation; and
• Deposition, in which water vapor is converted directly to ice.
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Satellite imagery, part 1
• Satellite imagery (both still images and video) is a
routine component of televised and Internet-based
weather reports.
• Satellite images are obtained from space-based
platforms that measure components of the
electromagnetic spectrum, primarily in the infrared
and visible range.
– The information obtained provides measurements of
temperature and humidity, and it allows meteorologists to
locate and track weather systems.
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Satellite imagery, part 2
• Satellite platforms:
– Geostationary satellites orbit the Earth about 36,000 km
above the surface.
• The speed with which they orbit the Earth matches the speed of the
Earth’s rotation, thus they “sit” in the same spot above the surface.
• The subsatellite point – the location on the Earth’s surface directly
below the satellite – is located along the equator.
• Two geostationary satellites, at 75 degrees W longitude and at 135
degrees W longitude, provide a complete view of much of North
America and adjacent portions of the Atlantic and Pacific oceans up
to about 60 degrees N latitude.
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Satellite imagery, part 3
• Satellite platforms (continued):
– Polar-orbiting satellites orbit the Earth between about 800
and 1,000 km above the surface.
• The orbital track crosses both North and South polar regions.
• Each successive north-south track overlaps with the western edges
of previous tracks, thus providing overlapping images of the Earth’s
surface.
• Sun-synchronous satellites pass over the same area roughly twice
every 24 hours.
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Satellite imagery, part 4
• Satellite imagery:
– Sensors on weather satellites typically measure reflected
sunlight or emitted infrared (IR) radiation.
– Visible images are essentially black-and-white photographs
of the Earth, with highly reflective surfaces – such as ice
caps or clouds – appearing bright white, and less reflective
surfaces – such as boreal forests or oceans – appearing
much darker.
• Cloud patterns on visible images are of particular interest, as
meteorologists can determine the stage of development of a storm
system in addition to its location.
• Useful visible imagery can only be obtained during daytime hours.
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Satellite imagery, part 5
• Satellite imagery (continued):
– Infrared images are essentially a measure of heat radiation
emitted by objects.
• Useful infrared imagery can be obtained at any time, day or night.
• Images are calibrated to show temperatures of objects in the field of
view.
– In black-and-white images, the coldest objects are bright white, while
the hottest objects are dark gray.
– In color images, the coldest objects appear blue and violet, while the
hottest objects appear red and orange.
– Low clouds can be differentiated from high clouds, as high clouds are
colder.
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Satellite imagery, part 6
• Satellite imagery (continued):
– Water vapor satellite images use special infrared sensors to
measure the amount of water vapor in the air.
• Water vapor does not appear on visible or on conventional infrared
sensors.
• Such images allow meteorologists to track movement of plumes of
moisture through the atmosphere.
• Current platforms measure water vapor concentrations between
altitudes of about 5,000 m and 12,000 m.
• A gray scale is used, so that little or no water vapor appears black,
while high concentrations appear milky white. Upper-level clouds
appear as bright white blotches.
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Sounding
• Satellite imagery (continued):
– Water vapor satellite images use special infrared sensors to
measure the amount of water vapor in the air.
• Water vapor does not appear on visible or on conventional infrared
sensors.
• Such images allow meteorologists to track movement of plumes of
moisture through the atmosphere.
• Current platforms measure water vapor concentrations between
altitudes of about 5,000 m and 12,000 m.
• A gray scale is used, so that little or no water vapor appears black,
while high concentrations appear milky white. Upper-level clouds
appear as bright white blotches.
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Models, part 1
• Models are often used in the effort to better
understand atmospheric and oceanic processes.
• A scientific model is an approximation or simulation
of a real-world system.
– A system is an entity that has components that function and
interact in an orderly and predictable manner that can be
described by fundamental physical principles.
– The Earth-atmosphere system is comprised of the Earth’s
surface features, plus that of the atmosphere.
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Models, part 2
• Models include only the essential elements (or
elements perceived to be essential) of a system.
– Construction of a model often helps scientists determine
which elements are essential or not.
– The simplicity of a model can help scientists gain important
insights into how a system works.
– Models can also be used to predict how a system might
respond to changes.
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Models, part 3
• Models may be classified as conceptual, graphical,
physical, or numerical.
– A conceptual model is an abstract idea that represents some
fundamental law or relationship.
– A graphical model compiles and display data in a manner
that readily conveys meaning (“A picture is worth a
thousand words.”).
– A physical model is a miniaturized version of a system.
• An salt water aquarium is a miniaturized version of a coral reef.
– A numerical model consists of one or more equations that
describe the relationship among variables in a system.
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Models, part 4
• All models simulate reality.
– A weather map portrays the state of the atmosphere at a
given time.
• Weather maps integrate observations from weather stations that
may be hundreds of kilometers apart.
– Weather satellites offer a more complete field of view, but
the spatial resolution of the satellites is limited.
– The predictions of numerical models may not be accurate
since we cannot model everything relevant to weather
processes.
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Human effects on the oceans
• Humans alter biogeochemical cycles.
– Waste products and pollutants produced by human
activities may have widespread effects.
• Agricultural and urban runoff may lead to nutrient pollution, which
in turn promotes algal growth and leads to reduced oxygen
concentrations available to other aquatic organisms.
– This happens every summer in the development of the Gulf of Mexico
dead zone off the coast of Louisiana.
– Pollutants may contaminate food supplies.
– Overconsumption of marine resources.
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