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University of Toronto St. George
Doug Thomson

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 earth’s 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 Sun’s 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 don’t 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 earth’s 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 Hihgly weathered tropical soils have low cation exchange capacities and little attraction Podsolization Process reduces fertility of the upper layers of soil Acidic soils occur in cool regions with needle-leaved trees. Decomposition of leaf little produces organic acids, which promote H+ ions,and rainfall usuall y exceeds precipitation Under moist conditions, water moves downward alot, and little clay forming material is transferred up to the surface. Posolized soils have reduced fertility! Laterization When clay particles break down, resulting in Si leaching, leaving oxides of Fe and Al in the soil The oxides give the soil a red colour Even though there is alot of H+ ions, they are neutralized by breakdown of clay particles Laterization proceeds on low-lying soils, where surface layers are NOT eroded Consequences: low cation exchange capacithy In absence of clay and organic matter, mineral nutrients are leached form soil When soils are weathered, new minerals are too far from surface to contribute to soil fertility The deeper the sources of nutrients, the poorer the surface layers Soil formation empahsizes role of the physical environemt ( climate, geology...) Ecologists in the Field Fires causes trees to go from coniferous to deciduous Deciduous established, &large quantities of Fe, Mg, and P was released, and finally, Ca increased in the sediment core, and trees took up Ca and enriched Ca content on top layers of soil. Sum up: soil retained its acidic, podsolized nature until the establishment of deciduous, and so the deciduous caused the soil to change. SOILS HIGHER IN CALCIUM, are LESS ACIDIC! The Biome Concept Of Ecology Convergence: unrelated organism evolve a resemblance to each other in response to environmental conditions. Biomes: biological communities and ecosystems characterised based on climate and plant form Two factors influence distributions of Species and Growth Forms: 1. Myriad Interactions- competition, predation, and mutualism 2. Chance & History – being apply to disperse in an environment and surviving. Climate is the Major Determinant of Plant Growth and Distribution Plants make adaptations: some are, plants in deserts have little or no leaves, and in temperate forests plants grow further apart, so they can spread their roots for competition for water Because some species are so well adapted to certain physical condition, it makes sense that they are limited to the types of environments in which they live in Example: Sugar Maple Tree- limited by cold winters, and hot summers, and drought summers. So its confined to northern portion of NA. Any attempts to grow this tree elsewhere will fail. Climate Defines The Boundaries Of Terrestrial Biomes Climate zone system: Heinrich Walter, based on annual cycle of temp and precipitation, has nine major division. SEE FIGURE 5.4 + 5.5 ON PAGE 91 + 92!!! STUDY THAT! Towards the drier end of the precipitation spectrum, Fire plays a distinct role in shaping plant communities, the influence of fire is great where moisture is available. Deserts and moist forests burn INFREQUENTLY. Grasslands and Shrublands have fires occasionally, and African savannahs and NA praries have frequent fires. After fires, new vegattion establishes! Water Climate Diagrams Distinguish The Major Terrestrial Biomes 20mm of monthly precipitation for each 10 degrees C in temperature provides sufficient moisture for plant growth ( see FIGURE 5.6 on PAGE 93) temp vs. Precipitation graph Equatorial Climates: seasonal distribution of wet and dry periods Subtropical Climates: warm and wet throught the year Tropical Climates: summer rains and winter droughts Meditteranian climates- winter rains and summer droughts Continental Climates: dry throughout the year and warm in summer Tropical Climates- warm temperature and summer rainfalls Temperate climate zones have average annual temperatures b/w 5 and 20 degrees C Temperate Seasonal Forest Biome : Referred to as deciduous forest, precipitation exceeds evaporation and transpiration, soils are podsolized and acidic. Low availability of nutrients, fires are frequent b/c soil is dry! Temperate Rain Forest Biome: Mild winters, heavy winter rains, summer fog . Tall evergreen forests. Temperate Grassland/desert Biome: rainfall, winters are cold, often called praries, and steppes (extensive grasslands). Infrequent precipitation, soil rich in organic matter. Grasses are dominant vegetation that grow over 2 m. Forbs are also abundant, b/c fires are dominant. Rhizomes found here ( fire-resistant underground stems). Winters are cold and summers are hot. In temperate deserts, evaporation and transpiration exceed precipitation; soils are dry, fries infrequent, low productivity of the plant community. Woodland/Shrubland Biome: found at 30-40 degrees north and south of equator, mild winter temperatures, winter rains, and summer droughts. Fires are frequent, climate supports thick evergreens with deep roots. Plants have fire- resistant seeds or crowns. SubTropical Desert Biome: areas with high atmospheric pressure associated with descending air of Hadley cells, very spare rainfall, high temperatures, long growing seasons. Low rainfall results in shallow soils. Do receive summer rainfall. These climate zones have average temperatures below 5C: Boreal Forest Biome: often called taiga, sever winters, evaporation is low, evergreen (needle-leaved). Because of low temperatures, plant little decomposes slowly, alot of organic carbon formed! Soils are acidic, STRONGLY podsolized, low fertility. Small growing seasons. Frost-tolerant vegetation. Tundra Biome: treeless permanently frozen soil (permafrost). Low precipitation, acidic soils, poor nutrient soils. Alpine tundra: longer growing seasons, higher precipitation, less sever winters, greater productivity, better-drained soils, higher species than Arctic tundra. These are climate zones with average temperature exceeding 20 degrees C: Tropical Rainforest Biome: always warm, a lot of rain, soil reddish colour, low nutrient, canopy of tall everygreens, have several understorys with smaller trees and shrubs, but very little of these because little hardly penetrates the canopy. You can also fin epiphytes + lianas, plants that grow on the branches and not rooted to soil. High temperature + abundant moisture leads to plant littler decomposing quickly, and vegetation quickly taking u the nutrientshigh productivity. However, when tropical rainforests are cut and burned, any nutrients go up in smoke and soils erode rapidly. In turn, environment degrades, and landscape become unproductive. Tropical Seasonal Forest/Savanna Biome: beyond 10 degrees from the equator, dry season, deciduous trees, dry season is longer and more sever, vegetation becomes shorter, progressively, vegetations turns into dry forest and then into true desert. In more humid tropical environments, soils are nutrient poor. Savaanas are grassland with scattered trees. Fire and grazing play important roles in maintaining savannah biome. Owe their character to the influence to human activities! Pages 204-207 Ecological Niche Modeling Predicts The Distribution of Species Ecological Niche Medlling: modeler starts by mapping unkown cocurences of a species in a geographic space, then catalogs the combination of ecological conditions (temperature + precipitation). This catalog is called ecological envelope. Then, the modeler can map the geographic area that has the same combination to predict the broader occurrence of the species within a region. Accuracy is evaluated by using a “training set” and a “test set”. This is used to predict the actual or potential distributions of species ( or newly introduced species, or even a population!) Global Change The average temperature of the earth has increased by 0.6 degrees These temperature changes COULD alter distribution of a species Research: most fish species moved northward were small-bodied, warmer temperatures are more hospitable to a greater variety of species, and warming of the North Sea allows more southerly species to expand the northern edges of their ranges into the area. Basically, this is a case involving an increase in diversity of a species. CHAPTER 2 Water is most abundant in earth., immense capacity to dissolve inorganic compounds, and so is an excellent medium for the chemical processes! Thermal properties of Water: stays liquid over a broad range of temperatures, temperature remains steady when heated or not. And it resists changes. 500 times the energy must be added to increase 1 degrees C of temp and 8- times as much heat is needed to lower the temp by one degree. Water become less dense as it cools, and upon freezing, expands. This property prevents lakes and oceans from freezing and enables aquatic plants and animals to find refuge there! The Density and Viscosity of Water -Because of their bones and proteins being denser than water would cause animals to sink, adaptation assure this does not happen. Many fish species have adapted into having appendages, gas-filled bladders and for plants gas-filled bulbs that allow them to float in water. - Aquatic animals have evolved streamlined shapes which reduce drag and allow movement in water. As animals become smaller, momentum of their movement decreases, and so many tiny marine animals have adapted appendages to prevent sinking (feathery projections that act like a parachute) Many Inorganic Nutrients Are Dissolved In Water organism require chemical elements to build necessary biological structures and maintain life Ultimatly, plats and animal can acquire required elements such as oxygen(below) from water! Nitrogen + sulfur: structural component of proteins Phosphorus: structural component of nucleic acids, bone Potassium: major solute in animals Calcium: structural component of bone and of woody material for plants Magnesium: structural component of chlorophyll Iron: structural component of haemoglobin + enzyme Sodium: major solute in extracellular fluid or animals The Solvent Capacity of Water Powerful solvent because water molecules are strongly attracted to solids (ions)! When these ions dissolve in water, they dissolve, and break apart. ( NaCl) The solvent properties of water are responsible for the presence of nutrients + minerals Water in most lakes and rivers has 0.01-0..02% dissolved minerals In oceansm calcium ions form calcium carbonate which eventually form limestone Hydrogen Ions In Ecological Systems Are very reactive! Play a crucial role in dissolving minerals from rocks and soils Concentration of H+ ions = acidity, measures as pH. Natural waters contain carbonc acid, weak acid, formed when Co2 dissolves in water Some natural waters have basic water because of excess of OH ions, but normal range is 6-9 However, sometimes, sulphuric acids pouring from mines can create a pH of as low as 4 H+ ions help dissolve minerals such as calcium carbonate which is SO important for snails athat use it to build their shells! Plants Obtain Water And Nutrients From the Soil By the Osmotic Potential of Their roots Soil Structure and Water-Holding Capacity Water molecules cling onto one another by hydrogen bonding and to surfaces of soil particles ( capillary action). This clinginess is the reason for why soil is able to retain water! Because clay particles, smallest, hold water tightly, less water is available to plants in a clay soil than in a soil with a mixture of particles, known as a loam. Water potential – strength of the forces holding water in soil Matric potential- attraction of water to the surfaces of soil particles (soil matrix) Soils with more clay and silt hold more water than coarse sand though which water drains By convention, water has potential ZERO!water always moves from high to low water potential. Soil has negative potential and so plants must develop a water potential lower than that of the soil to overcome the matric potential and extract water! Matric potential is greatest at the surfaces of soil particles and decreases with distance from them. Field capacity- amount of water held against gravity by matric potential of less than -0.01MPa Field capacity represent the max amount of water available to a plant in well-drained soil Wilting Coefficient or Wilting Point of Soil is -1.5 MPa [ plant cant remove water below this #] Osmotic Potential and Water Uptake By Plants Water moves from an area of low solute concentration to an area with high solute concentration This movement of water is called osmosis, and the force that attract water by osmosis is called osmotic potential. As water goes into the cell, the solute concentrations inside the cell would come out, and so there would be no net movemtn of water, simply equalization! So, in order to prevent equalizations, a semi-permeable membrane help (small go through) Second, cell membranes transport ions and small molecules actively against a con. gradient to maintain concentrations. This active transport expends ENERGY! A given mass of small solute molecule generates greater osmotic potential than the same mass of a larger molecule. Plants growing in deserts can lower their water potential to as much as -6MPa. Though, they pay a higher metabolic price, however, then they are able to maintain a high concentration of dissolved substances Forces Generated By Transpiration Help to Move Water from Roots To Leaves Plants conduct water to their leaves though xylem elements, which are empty remains of xylem cells in the cores of roots and stems, connected end-to-end to form the equivalent pipes. Osmotic potential in roots draws water from the soil into the plant causing root pressure that forces water into the xylem elements. But because of gravity, it can only raise water upto 20 m . Leaves themselves generate water potential when water evaporates from leaf cell surfaces! This is known as transpiration, and its water potential is -2 to -5MPa Cohesion-Tension Theory: 1.Water vapour diffuses out of stomata 2. Water evaporates from mesophyll cells 3. Tension pulls the water column upward and outward int he xylem of veins in the leaves, int he stem, and in the root . 4. Water molecules form a cohesive column in the xylem 5. Water moves into the root by osmosis then into the xylem - Plants prevent water loss by: a cuticle and closing and opening stomata (exit for water, entry for CO2) - Osmoregulation: maintain a salt balance, by getting rid of solutes such as salt after evaporation! Management of Salt Balance By Plants High salt load makes it difficult for roots to take up water, so plants must reduce salt conc To counter these problems: many mangroves maintain high concentrations of organic solutes (amino acids + sugar molecules) in roots and leaves to increase osmotic potential. Also, salt glands in leaves secrete salt by active transport to the exterior leaf surface or roots! Water Balance and Salt Balance in Terrestrial Animals Desert animal have champion kidneys: for instance, kangaroo rats, produce urine with solute concs as high as 14 times the levels in their blood, humans can only do 4 times as much. However, because sodium and chloride ions participate in the mechanism by which animal kidney retains water, the kidney does not excrete these ions efficiently. Hence, many animals lacking fresh water access have specialised salt-secreting organs. For i
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