Global Climates & Biomes Chapter 4 Global Climates & Biomes

Structure of the Atmosphere Density decreases as altitude increases (why?) Five layers of gases: Troposphere: 0 – 16 km (10 mi) Weather occurs here Temperatures drop with altitude Stratosphere: 16 – 50 km (10-31 mi) Higher altitudes are warmer (UV light) Ozone layer is located here Ozone = O3 Absorbs UV radiation Mesosphere Thermosphere Exosphere

Climate The average weather in a given region over a long time Affected by distribution of heat and precipitation Unequal heating of Earth’s surface: Due to the curvature of the Earth Angle of sun’s rays Albedo: the percentage of incoming sunlight that is reflected from a surface; white reflects, colors absorb Earth’s average = 30% Tropics = 10-20% Snow-covered poles = 80-95%

Atmospheric Convection Currents Four properties of air that determine circulation: Density – less dense (warm) air rises Water vapor capacity – warm air can hold more water vapor – max amount is saturation point Adiabatic cooling – air rises  pressure decreases  air expands in volume  expansion lowers air temp Adiabatic heating is the opposite Latent heat release – when water vapor condenses into liquid water, energy is released

Formation of Hadley Cells: a type of atmospheric convection current The sun heats moist tropical air, causing it to rise The rising air experiences adiabatic cooling, water vapor condenses into rain which falls back to Earth The condensation of water vapor produces latent heat release, which makes the air expand and rise farther The warm rising air displaces the cooler drier air above it, pushing it to the north and south The cool dry air sinks and experiences adiabatic heating. It reaches Earth’s surface as warm dry air and then flows back toward the equator.

ITCZ: intertropical convergence zone The area of Earth that receives the most intense sunlight Dense clouds and intense thunderstorm activity Not at a fixed latitude – moves with the sun’s angle throughout the year Located between 300 N and 300 S

Additional circulation cells Ferrel cells – 300 N & S to 600 N & S Polar cells - 600 N & S to the poles (900 N & S)

Besides all that, the Earth is spinning The equator rotates faster than the poles… This causes the winds to be deflected – this is the Coriolis effect http://www.youtube.com/watch?v=mcPs_OdQOYU

AND, the Earth is tilted on its axis The axis of rotation is angled 23.50 – the latitude that receives the most direct sunlight plus the most hours of sunlight changes throughout the year as Earth orbits the Sun Spring Equinox (March) – Sun directly overhead – all regions get 12 hours of light + 12 hours of dark – spring begins in Northern Hemisphere; fall in Southern Hemisphere Summer Solstice (June) – max tilt of Northern Hemisphere toward Sun – longest amount of daylight – summer begins Fall Equinox (Sept) – opposite of March – day & night equal Winter Solstice (Dec) – max tilt of Northern Hemisphere away from Sun – shortest daylight – winter begins

Don’t forget about all that ocean water! Ocean currents mix all the ocean waters and moderate the temperatures of the continents These are influenced by: temperature, gravity, prevailing winds, the Coriolis effect, & locations of continents Warm water expands – tropical water surface is about 8 cm (3 in) higher  water flows away from the equator Gyres – large-scale patterns of ocean circulation: clockwise in Northern Hemisphere; counterclockwise in Southern Upwellings – along the western coast of continents deeper , nutrient rich water rises – this supports large populations of producers and rich ecosystems Thermohaline circulation – mixes surface water with deeper water – related to differing salinities

Interaction of atmosphere & ocean El Nino-Southern Oscillation Every 3-7 years Surface currents in the Pacific reverse Global impact: Cooler & wetter conditions in SE U.S. Drier weather in southern Africa and SE Asia

Interaction of atmosphere & land Local features can impact climate Rain shadow Mountain range forces air up and over On the windward side, cooler air loses its moisture On the leeward side, air is drier  deserts

Terrestrial Biomes Biome – an area characterized by typical plants and animals adapted to the yearly temperature and precipitation Each biome contains many ecosystems whose communities are adapted to local variation in climate, soil, and other environmental factors

Deserts Evaporation > precipitation 30% of Earth Variations in annual temp (red) and precip (blue) in tropical, temperate, and cold deserts

Human Impacts on Deserts Large desert cities Soil salinization from irrigation Depletion of groundwater Land disturbance and pollution from mineral extraction Soil destruction from off-road vehicles

Forests – enough precip to support stands of trees Tropical warm temps high humidity photosynthesis year-round Temperate Deciduous forests: seasonal changes broad leaves dropped for cold winters Rain forests: evergreens in cool, moist environment Polar Taiga long, cold winters evergreens adapted to year-round photosynthesis

Human Impacts on Forests Clearing for agriculture, livestock grazing, timber, and urban development Conversion of diverse forests to tree plantations Damage from off-road vehicles Pollution of forest streams

Grasslands – less precip; fires common; soil extremely rich in temperate zone Tropical savanna Temperate prairie Polar tundra

Human Impacts on Grasslands Conversion to cropland Release of CO2 to atmosphere from grassland burning Overgrazing by livestock Oil production and off-road vehicles in artic tundra

Aquatic Ecosystems – affected by salinity, depth, and water flow Freshwater systems – low levels of dissolved salts Streams and rivers: from mountains to oceans Flow creates different conditions and habitats Headwaters: cold, clear, rapidly moving water with high levels of O2 Downstream: slower moving, less O2, warmer temps, more algae and cyanobacteria

Freshwater… Standing water: lakes and ponds Life found in layers – temperature, sunlight, dissolved O2, and nutrient availability changes with depth Littoral zone: shallow area around shore; rooted vegetation Limnetic zone: open offshore area; too deep for rooted plants; food chain begins with phytoplankton Profundal zone: deep water without light; food chain depends on organisms above Benthic zone: muddy bottom; nourished by decaying organic matter

Freshwater… Wetlands – land is submerged part or all of the year but is shallow enough for rooted vegetation throughout Swamps: contain trees Marshes: mainly nonwoody vegetation (cattails)

Marine biomes Estuaries Saltmarshes where rives flow into the ocean Nutrient rich areas due to river flow Mangrove swamps Also produce nutrient rich mud

Marine biomes… Intertidal zone Narrow strip between high and low tide mark on the coastline Difficult habitat for life

Marine biomes… Coral reefs Warm, shallow water beyond the shoreline

Marine biomes… The open ocean Sunlight cannot penetrate to the bottom Photic zone: enough light for photosynthesis Aphotic zone: lacks light and therefore photosynthesis