The Biosphere

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The Biosphere

• Chapter 56

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Outline

• The Sun and Atmospheric Circulation
• Atmospheric Circulation and Climate
• Major Biomes
• Patterns of Ocean Circulation
• Life in the Oceans
• Marine Ecosystems
• Freshwater Habitats
• Productivity of Freshwater Ecosystems
• Human Activity and Biosphere Stress
• Global Warming

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The Sun and Atmospheric Circulation

• Biome distribution results from the interaction
  of features of the earth and
• the amount of solar heat that reaches different
  parts of the earth and seasonal variations.
• global atmospheric circulation and resulting
  ocean current patterns.

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Relationships Between the Earth and Sun
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The Sun and Atmospheric Circulation

• Warm tropics
• Because the earth is a sphere, some regions
  receive more solar energy than others.
• Suns rays arrive almost perpendicular to the
  equator.
• Earths annual orbit around the sun and its daily
  rotation on its axis play important roles in
  climate.

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The Sun and Atmospheric Circulation

• Major atmospheric circulation patterns
• Warm air can hold more water vapor than cold air.
• Warm, moist air rises at the equator, cools,
  condenses, and falls as rain near the equator,
  and then flows back toward the poles.
• Air masses descend and produce arid zones at 30o
  N and S latitudes.
• rise again at 60o N and S latitudes

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Atmospheric Circulation
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Atmospheric Circulation and Climate

• Most of the major worlds deserts lie at 30o N
  and S latitude.
• Other major deserts are formed in the interior of
  large continents, or because of the rain shadow
  effect.
• Mountain ranges intercept moisture-laden air
  masses from the sea.
• The air mass rises, cools and drops rain on
  windward side.
• leeward side often much drier

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Rain Shadow Effect
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Atmospheric Circulation and Climate

• Latitude
• Because there are no seasons in the tropics,
  there is little variation in mean monthly
  temperature in tropical ecosystems.
• As you move away from the equator, sunlight
  strikes the earth at a more oblique angle, thus
  less sunlight falls on a given area.

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Atmospheric Circulation and Climate

• Elevation
• Temperature progressively becomes colder as you
  move up in elevation.
• 6o C for every 1000 m increase
• Microclimate
• very localized climatic conditions

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Elevation and Latitude
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Major Biomes

• Biomes are major communities of organisms that
  have a characteristic appearance and are
  distributed over a wide land area defined by
  regional variations in climate.

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Biome Distribution
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Major Biomes

• Biomes and climate
• Temperature and precipitation are two key
  parameters determining biomes.
• In the absence of geologic features and differing
  sea temperatures, each biome would form an even
  belt around the globe, defined largely by
  latitude.

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Predictors of Biome Distribution
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Major Biomes

• Tropical rain forests
• receive 140-450 cm annual rainfall
• contain at least half earths terrestrial plant
  and animal species
• Savannas
• seasonal rainfall (75-125 cm annually)
• dry tropical grassland transitioning from
  tropical rainforests to deserts

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Major Biomes

• Deserts
• less than 25 cm annual rainfall
• plants and animals adapted for water conservation
• Temperate grasslands (prairies)
• highly productive temperate regions
• herds of grazing mammals

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Major Biomes

• Temperate deciduous forests
• mild climates and plentiful rain
• perennial herbs
• Temperate evergreen forests
• cold winters and a strong, seasonal dry period
• nutrient-poor soils
• broad transitional zone

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Major Biomes

• Taiga
• long cold winter
• coniferous trees
• Tundra
• open, windswept, and boggy
• Permafrost (permanent ice) exists within a meter
  of the surface.

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Patterns of Ocean Circulation

• Ocean circulation determined by atmospheric
  circulation and location of land masses.

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Patterns of Ocean Circulation

• El Nino southern oscillation
• Pacific Ocean is normally fanned by constant
  east-west trade winds.
• Pushes warm surface water away from eastern
  coastal areas, and allows cold, nutrient-rich,
  water to well up.
• If winds slacken, warm water moves back inward,
  cutting off nutrient supply.
• Commercial fishing off Peru and Chile decreases
  dramatically.

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El Nino Winter
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Marine Ecosystems

• Oxygen supply can be critical in the ocean.
• As water temperatures rise, the amount of oxygen
  that can be held lowers.
• Carbon dioxide is extremely plentiful.
• uniform distribution of minerals
• Patchy bottom environment may contribute to
  species formation.
• 90 of living species are terrestrial.
• sharp habitat boundaries

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Marine Ecosystems

• Neritic zone
• Area less than 300 m below the surface along
  coasts of continents and islands.
• Intertidal (littoral) region is exposed to air
  when the tides recede.
• Nutrient runoff from the land near coastal
  regions contributes to productive continental
  shelf fisheries.

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Marine Ecosystems

• Pelagic zone
• Open sea supports a diverse biological community,
  primarily composed of plankton.
• most live in top 100 m
• light penetration
• Plankton collectively account for about 40 of
  all photosynthesis on earth.

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Marine Ecosystems

• Benthic zone
• Sea floor is a thick blanket of mud made up of
  sediment.
• Sea floor at depths below 1000 m, abyssal zone,
  has about twice the area of all the land on
  earth.
• Relatively recent discoveries have found high
  diversity of marine life living on sea floor near
  volcanic vents.
• chemosynthesis

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Marine Ecosystems
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Freshwater Habitats

• Inland lakes cover about 1.8 of the earths
  surface, and running water about 0.3.
• Ponds and lakes
• photosynthetic organisms limited to upper photic
  zone heterotrophic organisms occur in lower
  disphotic and aphotic zones
• littoral zone - shallow area along shore
• limnetic zone - surface water away from shore
• profundal zone - below light penetration

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Zones in Ponds and Lakes
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Freshwater Habitats

• In summer, warmer water forms layer over cooler
  water, forming an abrupt thermocline.
• In autumn, surface water temperature drops until
  it reaches temperature of cooler water
  underneath.
• upper and lower layers mix
• fall overturn

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Fresh Water Stratification
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Productivity of Freshwater Ecosystems

• Lakes divided into two categories
• eutrophic - rich in nutrients and organic matter
• oligotrophic - poor in nutrients and organic
  matter
• often deeper than eutrophic lakes, and very
  susceptible to chemical pollutants
• cultural eutrophication

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Productivity of Freshwater Ecosystems

• Wetlands support a wide variety organisms.
• play key ecological role by providing storage
  basins that moderate flooding
• many being disrupted by human activities

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Human Activity and Biosphere Stress

• Pollution
• Widespread modern agriculture introduces large
  amounts of chemicals into the global ecosystem.
• Chlorinated hydrocarbons (DDT) caused severe
  environmental problems due to biological
  magnification.
• eggshell thinning in predatory bird species

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Biological Magnification of DDT
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Acid Precipitation

• Sulfur introduced into the upper atmosphere
  combines with water vapor to produce sulfuric
  acid.
• Natural rain water rarely has a pH lower than
  5.6, but northeastern US has experienced rain
  with pH as low as 3.8.
• aquatic habitats, groundwater, and forests are
  all damaged
• solution is capturing emissions
• difficult and expensive

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Rainwater pH
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Destruction of the Tropical Forests

• More than half worlds population lives in the
  tropics, and the percentage is increasing.
• In mid -1990s, only about half of original
  extent of tropical rainforests existed in an
  undisturbed form.
• At current rates of clearing, all tropical
  rainforests will be gone in 30 years.
• loss of largely unknown levels of biodiversity as
  well as ecological functioning

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The Ozone Hole

• Ozone thinning was detected over Antarctica in
  1975.
• Major cause of depletion is chlorofluorocarbons
  (CFCs).
• Stratospheric ozone protects life from
  ultraviolet rays.
• 1 drop in atmospheric ozone is estimated to lead
  to a 6 increase in skin cancers.

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Antarctica Ozone Hole
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Carbon Dioxide and Global Warming

• Carbon dioxide and other gases trap longer
  wavelength infrared light, heat, radiating from
  the surface of the earth.
• greenhouse effect
• Roughly seven times as much carbon dioxide is
  locked up in fossil fuels as currently exists in
  the atmosphere.
• Estimated increases in atmospheric carbon dioxide
  would raise average global temperature 1.5-4.5o C
  by 2035.

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Effects of Global Warming

• Ecosystems
• prehistoric climate change
• Global temperatures changed as much as 10o C
  between extremes.
• range shifts in contemporary species
• life cycle changes
• Species
• dispersal ability
• reproduction cues
• temperature-sensitive sex determination

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Effects of Global Warming

• Humans
• rising sea levels
• climatic effects
• extreme events
• agriculture
• increased drought frequency
• reduced crop yields
• human health
• loss of safe drinking water
• mosquito-borne diseases

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Summary

• The Sun and Atmospheric Circulation
• Atmospheric Circulation and Climate
• Major Biomes
• Patterns of Ocean Circulation
• Life in the Oceans
• Marine Ecosystems
• Freshwater Habitats
• Productivity of Freshwater Ecosystems
• Human Activity and Biosphere Stress
• Global Warming

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