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Chapter 4 Global Climates and Biomes Earth’s climate system is composed of atmosphere/ocean interactions (driven by sun) Earth's Atmosphere Layers of the Atmosphere • Troposphere- the layer closest to Earth's surface and is the layer where we live; most of the atmosphere’s oxygen is found here. • The troposphere extends upwards 5 to 9 miles from the Earth’s surface at sea level. • Most weather occurs in the troposphere. • The troposphere is the most dense layer of the atmosphere (more molecules per unit of volume) Earth's Atmosphere Stratosphere- the layer directly above the troposphere. • The stratosphere extends from 9 to 31 miles from the Earth’s surface at sea level. • Stratospheric ozone is vital to trapping and scattering ultraviolet (UV) radiation from the sun. • This layer is drier and less dense than the troposphere. • The troposphere and stratosphere make up the lower atmosphere. 99% of all atmospheric air is found here. Earth's Atmosphere • Mesosphere lies directly above the stratosphere from 31-53 miles above the Earth’s surface at sea level. • Thermosphere is directly above the mesosphere, extending from 53-372 miles above the Earth’s surface. • Together the mesosphere and thermosphere are sometimes called the ionosphere. • Exosphere is the outermost layer of Earth’s atmosphere and acts as the transition zone between Earth’s atmosphere and outer space. Has the lowest atmospheric pressure of all layers. The Silly Mouse Tried to Escape Earth's Atmosphere • Composition of the Atmosphere • The atmosphere is made up of gases: Atmospheric gas Nitrogen (N) Oxygen (O) Water Vapor (H2O) Carbon Dioxide (CO2) Ozone (O3) % of the Earth’s Atmosphere 78% 21% 0-7% (varies by climate) 0.01-0.1% (varies by location) 0-0.01% (varies by location) Greenhouse Effect: The temperature of the Earth’s atmosphere is maintained by the absorption of incoming infrared radiation (heat) by atmospheric gases such as CO2 (carbon dioxide), CH4(methane), N2O (nitrous oxide) and O3 (ozone). Earth's Tilt and the Seasons • The Earth's axis of rotation is tilted 23.5 ˚. • When the Northern Hemisphere is tilted toward the Sun, the Southern Hemisphere is tilted away from the Sun, and vice versa. Earth's Rotation and the Coriolis Effect • As Earth rotates, its surface moves much faster at the equator than in mid-latitude and polar regions. • The faster rotation speeds closer to the equator cause a deflection of objects that are moving directly north or south. • Coriolis Effect- the deflection of an object's path due to Earth's rotation. Global Processes Determine Weather and Climate • Weather- the short term conditions of the atmosphere in a local area. These include temperature, humidity, clouds, precipitation, wind speed and atmospheric pressure. • Climate- The average weather that occurs in a given region over a long periodtypically several decades. Unequal Heating of Earth • As the Sun's energy passes through the atmosphere and strikes land and water, it warms the surface of Earth. But this warming does not occur evenly across the planet. Unequal Heating of Earth • This unequal heating is because: • The variation in angle at which the Sun's rays strike • The amount of surface area over which the Sun's rays are distributed • Some areas of Earth reflect more solar energy than others. (Albedo – the measure of the degree of reflection of heat from the sun off of a surface. Darker substances tend to absorb more heat and have a lower albedo while lighter substances tend to reflect more heat have a higher albedo) Atmospheric Convection Currents • Air has four properties that determines its movement: • Density- less dense air rises, denser air sinks. • Water vapor capacity- warm air has a higher capacity for water vapor than cold air. • Adiabatic heating or cooling- as air rises in the atmosphere its pressure decreases and the air expands. Conversely, as air sinks, the pressure increases and the air decreases in volume. • Latent heat release- when water vapor in the atmosphere condenses into liquid water and energy is released. The differences in temperature, density, and pressure of air/water determine movement patterns • Warm air/water rises & expands (low pressure) • Cold air/water is denser & sinks (high pressure) • Air’s saturation point for water falls as it cools (precipitation is “squeezed” out) Formation of Convection Currents • Atmospheric convection currents are global patterns of air movement that are initiated by the unequal heating of Earth. • Hadley cells- the convection currents that cycle between the equator and 30˚ north and south. • Intertropical convergence- the area of Earth that receives the most intense sunlight and where the ascending branches of the two Hadley cells converge. • Polar cells- the convection currents that are formed by air that rises at 60˚ north and south and sinks at the poles (90˚ north and south) • Look at the equator – as the air is warmed by the sun’s radiation, it rises and cools. As the warm, moist air rises and cools, the water vapor it contains condenses and falls as rain. This is why tropical rainforests are common along the equator • At 30º lat (N/S of the equator) notice that now cool air falls toward the earth. As that air falls and warms, it has a greater capacity for holding water and it absorbs water from the Earth's surface. • At 60º lat, the warm, moist air once again rises and cools dropping water toward Earth’s surface and causing temperate rainforest to be common in this location. • The final rotation of the cells results in cool, dry air descending over the poles, warming and pulling water from the land and leading to polar deserts. Ocean Currents • Ocean currents are driven by a combination of temperature, gravity, prevailing winds, the Coriolis effect, and the locations of continents. • Warm water, like warm air, expands and rises. • Gyres- the large-scale patterns of water circulation. The ocean surface currents rotate in a clockwise direction in the Northern Hemisphere and a counterclockwise direction in the Southern Hemisphere. Upwelling • Upwelling- as the surface currents separate from one another, deeper waters rise and replace the water that has moved away. • This upward movement of water brings nutrients from the ocean bottom that supports the large populations of producers, which in turn support large populations of fish. • Thermohaline circulation- another oceanic circulation that drives the mixing of surface water and deep water. • Scientists believe this process is crucial for moving heat and nutrients around the globe. Ocean surface currents (~10% of water movement): Subsurface thermohaline circulation ocean currents (90% of water movement) El Nino-Southern Oscillation • The El Niño-Southern Oscillation (ENSO) is a climate shift found in the tropical equatorial Pacific Ocean. • El Niño occurs when the trade winds blowing east to west across the equatorial Pacific Ocean slacken or reverse. This causes surface water to be warmer and suppresses nutrient rich upwelling off the northwest coast of South America (near Peru). If the upwellings are halted for more than 12 mths, population of plankton, seabirds, fish, etc. find it difficult to find enough nutrients to survive. As a result, their populaiton numbers decline. • ENSO events occur every three to seven years and last from a few months (normal) to as long as 4 years (extreme). • A strong ENSO can affect weather patterns over most of the Earth. • Warmer, dry weather may be found across much of the northern US, Canada, Brazil, Indonesia, Australia, India and southeast Africa leading to: Less snow, causing decreased snowmelt in the spring to replenish snow-fed rivers; severe droughts; increased wildfires; increased transmission of diseases due to stagnant warm water and lack of winter kill-off of insect vectors (malaria, dengue fever) and deterioration of fresh water in times of drought. • Significantly higher rainfall may occur across much of the southern US, Cuba, northern Peru, Ecuador, Bolivia, southeast Argentina, and equatorial east Africa leading to: suppression of hurricanes in the Caribbean and Atlantic Ocean; flooding which is often followed by landslides; increased transmission of diseases due to contamination of water sources because of flooding and standing water (mosquito breeding). • Variations in Climate Determine the Dominant Plant Growth Forms of Terrestrial Biomes • Climate affects the distribution of species around the globe. • Organisms possess distinct growth forms due to adaptations to local temperature and precipitin patterns. • Biomes- The presence of similar plant growth forms in areas possessing similar temperature and precipitation patterns. BIOME DISTRIBUTION Lakes and Ponds Lakes and Ponds • Littoral zone- the shallow area of soil and water near the shore where algae and emergent plants grow. • Limnetic zone- open water, where rooted plants can no longer survive. Phytoplankton are the only photosynthetic organisms. This zone extends to as deep as sunlight can penetrate. • Profundal zone- the zone where sunlight cannot penetrate and therefore producers cannot survive. • Benthic zone- the muddy bottom of a lake or bond beneath the limnetic and profundal zone. The Open Ocean • The depth that light can penetrate in the open ocean is dependent on the amount of sediment and algae suspended in the water. • Photic zone- the zone that receives enough light to allow photosynthesis to occur. • Aphotic zone- the deeper water that lacks sufficient light for photosynthesis. • Chemosynthesis- The process that occurs in the aphotic zone when some species of bacteria use methane and hydrogen sulfide to generate energy.