Download Ecology.Ch1and2.Lecture

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The sun is the ultimate source of energy that drives the global
climate system.
Energy gains from solar radiation must be offset by energy
losses if Earth’s temperature is to remain the same.
Much of the solar radiation absorbed by Earth’s surface is
emitted to the atmosphere as infrared radiation.
Earth’s surface is also cooled when water at the surface
evaporates and absorbs energy.
Latent heat flux: Heat loss due to evaporation.
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Near the equator, the sun’s rays strike Earth perpendicularly.
Toward the poles, the sun’s rays are spread over a larger area and
take a longer path through the atmosphere.
This establishes latitudinal gradients in temperature and is the
driving force for climate dynamics.
Solar radiation heats Earth’s surface, which emits infrared
radiation and warms the air above it.
Warm air is less dense than cool air, and it rises—this is called
uplift.
Atmospheric pressure decreases with altitude, so the rising air
expands and cools.
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Cool air holds less water vapor than warm air.
Rising air expands and cools, and water vapor condenses to form
clouds.
Condensation is a warming process, so the pocket of air stays
warmer than the surrounding atmosphere and enhances its uplift.
In summer, cumulus clouds form thunderstorms when there is
heating at Earth’s surface and progressively cooler atmosphere
above.
Thunderclouds reach to the boundary between the troposphere
and stratosphere, where temperatures are warmer.
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Tropical regions receive the most solar radiation and the most
precipitation.
Uplift of air in the tropics results in a low atmospheric pressure
zone.
When air masses reach the troposphere–stratosphere boundary,
air flows towards the poles.
Subsidence: Air descends when it cools and forms a high
pressure zone at about 30°N and 30°S.
Major deserts of the world are at these latitudes.
Hadley cells: Large scale circulation patterns resulting from
uplift in the tropics.
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Other atmospheric circulation cells:
Polar cells at the North and South Poles—cold air descends,
creating high pressure zones with little precipitation (polar
deserts).
Ferrell cells exist at mid-latitudes.
These atmospheric circulation cells result in the major climatic
zones in each hemisphere—tropical, temperate, and polar
zones.
Winds flow from areas of high pressure to areas of low pressure,
resulting in consistent patterns of air movements called
prevailing winds.
The winds appear to be deflected due to the rotation of the Earth
—the Coriolis effect.
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Water has a higher heat capacity than land—it can absorb and
store more energy without changing temperature.
Summer: Air over oceans is cooler and denser, so air subsides
and high pressures develop over the oceans.
Winter: Air over continents is cooler and denser; high pressure
develops over continents.
These are known as semipermanent high and low pressure cells.
Seasonal shifts in pressure cells influence the direction of the
prevailing winds.
Major ocean surface currents are driven by surface winds, so
patterns are similar.
Speed of ocean currents is about 2%–3% of the wind speed.
Your text has a few more simple charts
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Vertical ocean circulation:
Surface waters are warmer and less saline (less dense) than deep
waters, so the two layers generally do not mix.
Where warm tropical surface currents reach polar areas, the
water cools, ice forms, the water becomes more saline and more
dense and sinks (downwelling).
The downwelling water mass moves back toward the equator,
carrying cold, polar water.
Upwelling occurs where deep ocean water rises to the surface.
Upwelling occurs where prevailing winds blow parallel to a
coastline. Surface water flows away from the coast and deeper,
colder ocean water rises up to replace it.
Upwellings influence coastal climates.
Upwellings bring nutrients from the deep sediments to the photic
zone, where light penetrates and phytoplankton grow.
This provides food for zooplankton and their consumers.
These areas are the most productive in the open oceans.
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Ocean currents influence regional climate.
The warm Gulf Stream and North Atlantic Drift warm the
climate of Great Britain and Scandinavia.
At the same latitude, Labrador is much cooler because of the
cold Labrador Current.
Ocean currents transfer heat from the tropics to the poles.
The “great ocean conveyer belt” is an interconnected system of
ocean currents that link the Pacific, Indian, and Atlantic oceans.
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Average annual temperatures become progressively cooler from
the equator toward the poles.
This pattern is altered by ocean currents, continental topography,
and the distribution of land and water masses.
Air temperatures over land show greater seasonal variation than
those over the oceans, with warmer temperatures in summer and
colder temperatures in winter.
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Lapse rate: Temperature decreases with elevation.
Air pressure and density decrease with elevation; there are fewer
air molecules to absorb infrared radiation.
Wind speed also increases at high elevations due to less friction
with the ground surface.
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Precipitation patterns associated with the atmospheric circulation
cells are modified by mountain ranges and semipermanent highand low-pressure zones.
Pressure cells influence movement of moist air from oceans to
continents and cloud formation.
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Coastal areas have a maritime climate—little daily and seasonal
variation in temperature, and high humidity.
Areas in the center of large continents have continental climates
—much greater variation in daily and seasonal temperatures,
especially in temperate zones.
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On mountain slopes, shifts in vegetation type reflect climate changes as
temperature decreases and precipitation and wind speed increase with
elevation.
When air masses meet mountain ranges, they are forced upward, cooling
and releasing precipitation.
North–south trending mountain ranges create a rain shadow effect: The
windward slope facing the prevailing winds has high precipitation and
lush vegetation; the leeward slope gets little precipitation.
East-facing slopes receive more morning sun and become warmer than
the surrounding slopes and lowlands.
This differential heating creates localized upslope winds.
Clouds may form and produce thunderstorms that move into surrounding
lowlands.
At night, cooling is greater at higher elevations, and cold, dense air flows
downslope and pools in low-lying areas.
Valley bottoms are the coldest sites in mountainous areas during clear,
calm nights.
Cordilleras—large mountain chains—can channel movement of air
masses.
The Rocky Mountains steer cold Arctic air through central North
America and inhibit its movement through the intermountain basins to
the west.
Vegetation can also influence climate.
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Albedo: Amount of solar radiation a surface reflects; light-colored
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The texture of Earth’s surface changes with vegetation.
A continuous grassland has a smooth surface, which allows greater transfer
of energy to the atmosphere by wind than a rough surface, such as mixed
forest and grassland.
Evapotranspiration: Water loss through transpiration by plants, plus
evaporation from the soil.
It transfers energy (as latent heat) and water into the atmosphere, thereby
affecting air temperature and moisture.
Decreased evapotranspiration results in less moisture in the atmosphere
and less precipitation.
Deforestation in the tropics can lead to a warmer, dryer regional climate.
Loss or change in vegetation can affect climate.
Deforestation increases albedo of the land surface: Less absorption of solar
radiation and less heating.
Lower heat gain is offset by less cooling by evapotranspiration, due to loss
of leaf area.
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Climate has varied over hundreds and thousands of years.
These variations have influenced the evolutionary history of organisms and
the development of ecosystems.
Earth is tilted at an angle of 23.5° relative to the sun’s direct rays.
The angle and intensity of the sun’s rays striking any point on Earth change
as Earth orbits the sun, resulting in seasonal variation in temperature and
length of day, especially in temperate and polar zones.
The difference in seasonal solar radiation increases from the tropics toward
the poles.
Seasonality influences biological activity and distributions of organisms.
In the tropics, seasonal changes in solar radiation are small.
Seasonal changes in precipitation result from movement of the
Intertropical Convergence Zone (ITCZ), the zone of maximum solar
radiation and atmospheric uplift.
The ITCZ moves from 23.5°N in June to 23.5°S in December.
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Aquatic environments also experience seasonal changes in
temperature.
Water is most dense at 4°C. Ice has a lower density and forms on
the surface.
Ice has higher albedo than open water and prevents warming of
the water.
Oceans and lakes can become stratified—warm surface water
on top of colder, denser water results in layers that do not mix.
Stratification determines the movement of nutrients and oxygen;
both are important to organisms.
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In temperate-zone lakes, stratification changes with the seasons.
In summer, the warm epilimnion lies over the colder
hypolimnion. The thermocline is the zone of transition.
Complete mixing (turnover) occurs in spring and fall when
water temperature and density become uniform with depth.
El Niño events, or the El Niño Southern Oscillation (ENSO),
are longer-scale climate variations that occur every 3 to 8 years
and last about 18 months.
The positions of high- and low-pressure systems over the
equatorial Pacific switch, and the trade winds weaken.
The trade winds normally push warm surface water toward
Southeast Asia. During El Niño, this is reversed.
Upwelling of deep ocean water off the coast of South America
ceases, resulting in much lower fish harvests.
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La Niña events are stronger phases of the normal pattern, with
high pressure off the coast of South America and low pressure in
the western Pacific.
They usually follow El Niño, but tend to be less frequent.
ENSO is connected with unusual climate patterns, even in
distant places, through its complex interactions with atmospheric
circulation patterns.
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The North Atlantic Oscillation is a similar atmospheric
pressure–ocean current oscillation that affects climate in Europe,
northern Asia, and the eastern coast of North America.
The Pacific Decadal Oscillation (PDO) affects climate around
the North Pacific.
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Long-term climate change:
Over the past 500 million years, Earth’s climate has alternated
between warm and cool cycles.
Warmer periods are associated with higher concentrations of
greenhouse gases.
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Earth is currently in a cool phase, characterized by regular
periods of cooling, including formation of glaciers (glacial
maxima), followed by warming periods with glacial melting
(interglacial periods).
These glacial–interglacial cycles occur at frequencies of about
100,000 years.
We are currently in an interglacial period; these have lasted
about 23,000 years in the past.
The last glacial maximum was about 18,000 years ago.
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The glacial–interglacial cycles have been explained by regular
changes in the shape of Earth’s orbit and the tilt of its axis—
Milankovitch cycles.
The intensity of solar radiation reaching Earth changes,
accentuating seasonal variation and resulting in climatic change.
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The shape of Earth’s orbit changes in 100,000-year cycles.
The angle of axis tilt changes in cycles of about 41,000 years.
Earth’s orientation relative to other celestial objects changes in
cycles of about 22,000 years.
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Salinity: Concentration of dissolved salts in water.
Salts are composed of positively and negatively charged ions
that disassociate when placed in water.
Salts affect the ability of organisms to absorb water.
Salts can also be nutrients.
Salinity of the oceans varies from 33 to 37 ppt.
It varies as a result of evaporation, precipitation, and sea ice
melting.
Salinity is highest near the equator and decreases at high
latitudes.
Ocean salts consist mainly of sodium, chloride, magnesium,
calcium, sulfate, bicarbonate, and potassium.
They come from gases emitted by volcanic eruptions early in
Earth’s history and from the gradual breakdown of minerals in
Earth’s crust.
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Some inland lakes become more saline over time, reflecting a balance
between precipitation, evaporation, and inputs of salts.
Inland “seas” in arid regions (e.g., the Dead Sea and Great Salt Lake) can
have higher salinity than the oceans.
Soils near oceans can have high salinity—salt marshes and tidal estuaries.
Salinization: Soils in arid regions become saline when water is brought to
the surface by plant roots or irrigation and high rates of evapotranspiration
result in salt build-up.
Acidity: Ability of a solution to act as an acid—a compound that gives up
protons (H+) to a solution.
Alkalinity: Ability of a solution to act as a base—a compound that takes
up H+ or gives up hydroxide ions (OH–).
Acidity and alkalinity are measured in pH:
–log10 of the concentration of H+
pH of water influences metabolic functions and the chemistry and
availability of nutrients.
Organisms have a limited range of pH tolerance.
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