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

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University of Toronto St. George
Ingrid L.Stefanovic

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 cells! 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. 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. 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 THERMOCLINE. 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 hypolimnion. 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 El Nino is followed by La Nina, period of strong trade winds that bring extreme weather, and upwelling currents, and heavy rainfall, and drought in north-temperate resgions, and increase in hurricane activity. Cold waters in the Pacific weaken subtropical jet stream, and strengthen polar jet stream. Ecologists in The Field: Scientists are using idotopes to determin past climate activity Isotopes of O, C and other elements in ocean sediments ( act like tiny thermometre over time) Climate And Underlying Bedrock Interact To Diversify Soils Climate affects soil which affect distribution of plants and animals Characteersitic fo soild determine its ability to hodld water and have minerals Soil has distinct layers called horizons: O: dead organic litter A:humus, decomposed organic material E: minerals, plant roots, Elviation occurs here: downward movment of dissolved material B- little organic material, clay minerals, oxides of Al and Fe out of E horizon ( illuviation) C- weakly altered material, Ca and Mg carbonates R- unaltered parent material Factors that determine characteristics of soil: climate, parent material, vegetation, local topography [landscape] , and age. As soil gets deeper, climate has a lower effect on it When little rain falls, parent material breaks down. Thus, dry regions have shallow soils! Weathering Physical +chemical alteration if rock material near earths surface Repeated freezing and thawing of water breaks down rocks, and exposes them to chemical action. Soluble minerals such as NaCl and CaSO4 dissolve. Key aspect of weathering: displacement of certain elements in these minerals This process provides baiscal mineral structure of soil When Mg ad Al are replaced by H and Fe, clay gains negative charge, and they hold positive cations, this ability to retain cations in soil is called cation exchange capacity Hydrogen ions come from : carbonic acid in CO2 and when organic matter oxidizes
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