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Notes For the Book Economy of Nature...All required chpters

Course Code
Ingrid L.Stefanovic

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Hadley Circulation
Warming air expands, becomes less dense and rises. As air heats up, evaporation quicken because equilibrium water
vapour increases (doubling with every 10 degrees rise in temperature)
As the air reaches the upper layers of the atmosphere, (10-15km), it spreads north and south toward higher latitudes.
This air is then replaced from below by surface-air
The In the upper atmosphere, the rising air cools and expands, and becomes dense enough to go back to the earths
surface and spread N and S. Thus completing a cycle.
One Hadley cell is formed right o the equator and one left to it.
Hadley cells drive other secondary cells, such as polar and Ferrell cells).
Hadley cells are between 0 degrees and 30 degrees. Ferrell cells are between 30 and 60 deg.
Coriolis Effect + Jet Streams!
Explains why winds go from NE to SW
A jet stream is formed when cool air from higher latitudes moving towards the equator mixes with warm air in the
upper atmosphere, 10 km above the earths surface at the equator, causing a rapid air current from west to east.
The formation of a jet stream is not well understood; however, it may because by the junction of Ferrell and Hadley
Similarly, the junction of polar and ferrel cells create another jet stream. These are very strong and have an
unpredictable influence on the weather!
Intertropical Convergence and SubTropical High-Pressure Belt
Intertropical converge- at the equator, where air from the northern hemisphere and southern hemisphere meet.
Reason tropics are humid: warm air rises, begins to cool and so precipitation occurs
The air masses moving away from the intertropical convergence have lost much of their water to precipitation, and
because air has cooled, it sinks and creates a high atmospheric pressure in regions known as subtropic H-P belts.
Subtropical high-pressure belts (30 N and S of equator) – all deserts fall her
Why? Because the air that sinks draws moisture from the land
Ocean Currents Redistribute Heat
winds cause variation in marine conditions
direction of ocean circulations is like the coriolis effect: oceans currents go to the right (CW) in the Northern
Hemisphere, and left (CCW) in the southern hemisphere.

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As surface currents move apart, they draw water from deeper layers. Surface water moves away from land, and is
replaced by water from below. Deep water is rich in nutrients, thats why upwelling zones have high biodiversity
Upwelling: when surface currents diverge ( region of high biodiversity)
Upwelling can be seen on western coasts of continents
Thermohaline Circulation
Responsible for global movement of great masses of water between major ocean basins.
Wind-driven surface currents moves toward higher latitudes, water cools and become dense.
As it goes north, water freezes, and salt concentration of the underlying water rises, and the cold water becomes
dense and sinks known as North Atlantic Deep Water. Eventually, these waters flow back to the equatorial regions.
Thermohaline circulation is also responsible for distrubting heat energy from the tropics to higher latitudes.
Also known as ocean conveyor belt
Shutdown of Thermohaline Circulation and the Younger Dryas
Concern: melting og Greenland ice sheet and Srctic ocean will cause flooding and prevent thermohaline circulation!
Such an event happened about 12700 years ago. Glaciers melted, and the water flooded to seam cutting off the
thermohaline circulation. Result: cold weather called the younger dryas period lasting 1300 years!
Continental drift : alters flow of ocean currents chanign distribution of heat
Latitudinal Shifting of The Suns Zenith Causes Seasonal Variation in Climate
N-ward and S-ward movement of solar equator determines rainy seasons
Intertropcal convergence belt follows solar equator producing a belt of rainfall
So, wet and dry seasons are most obvious about 20 degrees N and S of equator
Movement of these cause two seasons of heavy rainfall at the equator, and a single rainy season alternating with an
obvious dry season at eth edges of the tropics.
Mediterraniean Climate: drought-summer, rainfall-winter
Temperature-Induced Changes in Water Density Drive Seasonal Cycles in Temperate Lakes
Water gains and loses heat slowly, and so temperature change in oceans is not that fast
When winters are cold and summers are hot, a lake undergoes 2 periods of vertical mixing and 2 periods when the
water is layered, with little vertical mixing
During the winter, a lake has a temperature profile. That is, coldest water (0 degrees)lies at the surface, just beneath
ice. Warm water sinks to the bottom to as much as 4 degrees C.

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In spring, the water is warmed by the sun until surface temperature excees 4 degrees, this water sinks and the deep
water rises, and that is vertical mixing.
This is called spring over turn, brings nutrients above and takes O2 to the bottom!
In summer, sun rises higher each day, surface water heats faster, , this depth where temp. changes most is
The warmer, less dense water just floats on top of the dense, cool water below. This condition is known as
stratification ( lakes must be more than 5 m deep to experience this!)
May be located anywhere between 5 and 20m below surface.
Upper layer of warm water above thermocline is called epilimnion, and deeper cold water below it is called
Epilimnion most production happens here, oxygen is most found here, so this are is suited for animal life.
However, planst and alge deplete the supply fo minerals here. So, most animals and bacteria remain BELOW
thermocline, where there is little photosynthesis, & deplete oxygen there.
In late summer, productivity of lakes decreases, and oxygen + nutrients deplete
In fall, surface water cools of lakes, and sinks as it becomes dense. This vertical mixing is known as the fall
overturn. Fall overturn speeds O2 below, and nutrients above. This causes an explosion oh phytoplankton (aka fall
autum bloom!)
Vertical mixing of lakes is less dramatic in lakes that are not exposed to continental climates.
Lake temperatures that dont fall below 4 degrees, only have ONE mixing event each year.
In tropical lakes, vertical mxing occurs ALOT. In temperate zones with deep lakes, vertical mxing hardly occurs,
and so they have no productivity!
Concern: tropical region lakes increase temp. Of surface water, and create thermocline at shallow depths 
impairing vertical mixing and so reducing lake production!
Climate and Weather Undergo Irregular and Unpredictable Changes
- El nino- warm countercurrent, moves down the coast toward peru. Flows stongly and far enough to force the Preu
Current offshore and shutdown fishing indrusty
During normal years, without el nino, peru current warms up as the current moves westward across equatorial
pacific ocean.
El nin is triggered by Southern Osicllation: reversal of pressure areas
Result: westward-flowing wind reverses or stop
El Nino causes strong Hadley Cell circulation, resulting in stormy weather. Polar jet streams weaken, causing warm
and dry conditions in southern Canada and Alaska
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