LIFESCI 7B Lecture 10: Week 10
10 Jun 2018
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Week 10
48.1: Physical Basis of Climate
● climate= Long-term average weather
The principal control on Earth’s surface temperature is the angle at which solar radiation strikes the surface.
● Earth at perfect position and perfect temp for liquid water to exist
● Warm temperature at equator, cold at poles; temp distribution result of incoming solar radiation--sun
strikes equitorial regions directly but strikes higher latitudes at more of an angle (causing same amount
of light to be distributed across wider angle
○ amount of solar energy striking a given area in the tropics is about twice that found near the
poles, and so tropical regions are warmer
○ Higher latitudes→ lower temp AND greater variation through the year
● Seasonality a result of earth’s rotational axis (23.5)
○ patterns of temperature variation through the year go a long way toward explaining the
geographic distribution of biomes across the globe
● topography The physical features of Earth;
○ also contributes to global temperature patterns (e.g. temperature declines with increasing
elevation)
■ temperature drops about 4°F for every 1000 feet in elevation (6.5°C per kilometer)
■ Mountains therefore exhibit a pattern in which climate and biomes change as elevation
increases, mirroring the spatial pattern from lower to higher latitudes.
Heat is transported toward the poles by wind and ocean currents.
● Temps at equators are cooler than predicted, temps at poles are warmer than predicted
○ → result of wind and ocean currents that transport heat from low to high latitudes
● Warm air→ faster moving molecules→ less dense→ air rises, which then cools down at a certain latitude
and stops rising but spreads towards poles to about 30*N; from here, some air warns and returns either
to equator (0*) or 30* closer to poles (so 60* latitude)
○ Rise of warm air particularly strong at equator
○ Warm air rises→ cool air rushes in to replace it→ wind; direction of wind depends on latitude and
earth’s rotation about an axis
● Coriolis effect The phenomenon in which, because of Earth’s counterclockwise rotation about its axis,
winds and oceanic currents in the Northern Hemisphere
deflect to the right, and those in the Southern Hemisphere
deflect to the left.
○ Due to different points on different latitudes going at
different speeds (equator=greatest speed)
● wind→ surface currents in ocean→ transports more heat from
equator to poles
○ Cold water sinks below warmer water and moves
more slowly→ 3D circulation of water through Earth’s
oceans that plays an important role in the
determination of regional climates
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● Wind and water transfer heat from the equator toward the poles, modifying the direct effects of solar
radiation→ temperature distribution observed across the planet
○ But not the only factor in distribution of biomes
Global circulation patterns determine patterns of rainfall, but topography also matters.
● Warm air can carry more water vapor than can cold air→ global rainfall patterns
○ Rising warm air carries vapor, when the air cools, water condenses and it rains
○ descending air takes in water vapor as it warms near earth’s surface→ water vapor taken in
instead of being released→ arid (dry) climate
○ rising/falling of air govern distribution of
rainfaill
● rain shadow The area on the lee (sheltered) side of
mountains, where air masses descend, warming and
taking up water vapor; as a result, lands in the rain
shadow are arid.
○ Dry area on lee side of mountain ranges
○ Wet air from oceans moves up mountains
and cools→ releases moisture as rain
○ Air then moves down mountain, warms, takes
up water vapor→ dries the area in rains shadow
● regional climate reflects the interactions among solar radiation, global patterns of circulation, and
Earth’s varying topography. Biomes, in turn, reflect these variations in climate.
48.2: Biomes
● Biomes are recognized by their characteristic communities—most visibly their vegetation, which relfects
evolutionary adaptation of plant form and physiology to climate
Terrestrial biomes reflect the distribution of climate.
● Evapotranspiration: sum of evaporation directly from soils and water bodies plus the amount
transpired by plants→ returns a large amount of water vapor to the atmosphere.
○ Recall physiological tradeoff of plants
○ potential evapotranspiration The amount of evapotranspiration that temperature, humidity,
and wind would cause if water supply weren’t limiting; the demand on the water resources of an
ecosystem. (precipitation reflects water SUPPLY)
■ potential evapotranspiration ratio In an ecosystem: ratio of water demand to supply
→ tells us what type of vegetation can be supported in a given region
○ Deserts have high potential evapotranspiration (up to 20+); limited water/high demand→ plants
must keep evapotrasnpiration (and photosynthetic rate) minimized → plants that store water
○ Rainforests have low potential evapotranspiration (as low as 0.2) → allows development of wet
forests w/ high biomass → high evapotranspiration and high photosynthetic rates
○ Intermediate potential evapotranspiration:
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● Both latitude and altitude influence the potential evapotranspiration ratio through their effects on
temperature and precipitation, and the combined effects of these factors are reflected in the distribution
of biomes around the world
● Similar biomes→ similar plant form, but not often closely related→ convergent evolution as result of
similar environment
○ In terrestrial biomes, vascular plants dominate primary production, although mosses, lichens,
algae, and cyanobacteria also contribute
○ Plants also provide a physical structure for the biome (tall plants→ wet temperate/tropical
forests, short plants→ water is more scarce/short growing season)
○ Food chain in terrestrial biomes
● TERRESTRIAL BIOMES: Tundra, Alpine, Taiga, Temperate Coniferous Forest, Deciduous Forest,
Temperate Grassland, Desert, Chaparral, Savanna, Tropical Rain Forest
○ Often characterized by carniverous vertabrates that live there (lions, tigers, wolves)
○ In all terrestrial biomes, detritus from both plants and animals ends up in ground and may
acculmulate in soil
Aquatic biomes reflect climate, and also the availability of nutrients and oxygen and the depth to which sunlight
penetrates through water.
● Water is denser than air; primary produers can rely on buoyancy for mechanical/mechanical support
(no need for wood), not bound by gravity nutrients all around them (when close to sunlight)
○ structure and distribution of primary producers governs patterns of consumer organisms
■ Aquatic plants and macroscopic algae→ important primary producers in shallow aquatic
environments where they can take advantage of nutrients transported from land while
remaining anchored to the riverbed, lakebed, or seafloor
■ Most productivity near surface where light penetrates
● much plant, algal, and animal debris accumulates in sediments, supporting
luxuriant growth by bacteria.
■ In larger lakes and the open ocean, phytoplankton—photosynthetic microorganisms that
float in sunlit waters—are predominant primary producers, combining high rates of
primary production with low biomass
● FRESHWATER BIOMES: Lakes, Rivers
○ vary tremendously in climate, and also in nutrient input and oxygen availability.
○ turbulent flow of water ensures that rivers are well oxygenated.
○ Some lakes, however, are physically stratified, meaning that the density of bottom waters keeps
them from mixing upward with shallow waters
○ Only about 2.5% of Earth’s water is fresh, and most of this water occurs in glaciers, permafrost,
and groundwater within soils
● REPRESENTATIVE MARINE BIOMES: Intertidal, Coral Reefs, Pelagic Realm, Deep Sea
○ oceans constitute Earth’s largest biomes. In fact, the oceans are so large and so diverse in their
biology that ecologists commonly subdivide them into distinct realms based on depth and
proximity to the shoreline
■ Oceanic dimensions determine the distribution of nutrients, oxygen, and light
● photic zone The surface layer of the ocean through which enough sunlight
penetrates to enable photosynthesis.
○ Viruses play a particularly large role in marine biomes, lysing up to 30% of phytoplankton daily
in coastal ecosystems and releasing large amounts of organic molecules into the water column.
○ Only surface of ocean is well oxygenated
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