Transcript L50-the_hydrosphere-ch6

The Hydrosphere
Observatory textbook pages 200 to 213
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2. The Hydrosphere
• The hydrosphere consists of the Earth’s
water resources: oceans, lakes, rivers,
streams, groundwater, and glaciers
• 97.5% of water on Earth is salt water
• Only 2.5% is freshwater!
• Fig. 6.26 on p. 201
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2.1 Inland Waters
• Inland waters are all the freshwater
resources found on the continents (lakes,
rivers, groundwater)
• A watershed is an area of land in which
all inland waters drain into the same larger
body of water (also called catchment area
or drainage basin)
• eg: St.Lawrence River watershed
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What is a watershed?
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St. Lawrence River Watershed
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Factors that affect how water
flows within a watershed
• Topography slope of the land; steep
slopes drain easily and quickly
• Geology type of rock; holes or gaps in
rock vs. compact clay
• Climate rainfall, winds and temperature
• Vegetation highly vegetated areas can
slow water flow
• Development a dam can prevent water
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2.2 The Oceans
• Five major oceans
– Pacific Ocean
– Atlantic Ocean
– Arctic Ocean
– Indian Ocean
– Southern Ocean (as of 2000)
** Two important factors when studying oceans
are temperature and salinity
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Ocean Temperature
• Ocean temperature varies with depth,
season and latitude
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Depth
• Sunlight warms the top layer of ocean
water which is called the mixed layer
• Below 200m temperature drops quickly;
this zone of rapid temperature change is
called the thermocline
• Beneath the thermocline at about 1000m,
water temperatures are uniformly cold at
about 4oC
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Ocean Temperature and Depth
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Season
• Oceans warm slightly in summer and cool
slightly in winter.
• The changes in temperature are less
pronounced than on the land because
water loses or gains heat much more
slowly than land.
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Latitude
• Ocean waters are 25oC to 28oC at the
equator and only 12oC to 17oC in the
temperate zones.
• They are colder still at extreme northern
and southern latitudes (<10oC).
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Ocean Salinity
• Salts dissolved from the lithosphere create
a salty ocean. These salts dissolve as
rivers flow over the ground and empty into
the ocean.
• Salinity is a measure of the amount of salt
dissolved in a liquid.
• Ocean salinity is about 3.4 to 3.7%
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Ocean Circulation
• Water in the ocean is in constant motion.
• An ocean current is the movement of
seawater in a certain direction.
• Ocean circulation is the combined effect
of all currents that move in oceans.
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Surface Currents
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Wind driven ocean currents
Push the top 400m of water
eg: The Gulf Stream current
See map diagram on p. 204-205 of
Observatory
Ocean surface currents
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Subsurface Currents
• Occur at depths of more than 800m
• Due to variations in density between
layers of water
• Cold water is more dense and tends to
sink
• High salinity water is also more dense and
sinks below less saline water
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Thermohaline Circulation
• The combined effect of surface and
subsurface currents is termed
thermohaline circulation
• Results in water being moved all around
the globe
• Accounts for major transfers of heat
• Dramatically affects global weather
patterns
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2.3 The Cryosphere
• The cryosphere is all the frozen water on
the surface of the earth (pack ice, glaciers,
frozen lakes, permafrost).
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Pack Ice
• Composed of the ice floating on the
oceans near the North and South poles
• Extent of pack ice changes with seasons
• Due to the effect of global warming the
extent of pack ice is shrinking
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Glaciers
• A glacier is a mass of ice on land, formed by
compressed snow
• Contain 79% of world’s freshwater
• Largest glaciers are at the poles (eg: Greenland
icecap), but some smaller glaciers exist in
mountain ranges (eg: in BC and Alberta)
• Glaciers are also melting at a fast rate due to
global warming
• The melting of glaciers and pack ice may lead to
a rise in sea level and consequent flooding of
low lying lands (eg: Florida)
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A high alpine glacier
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2.4 Energy Resources from the
Hydrosphere
• Hydraulic energy energy derived from
moving water
• Three main sources of hydraulic energy:
rivers, waves and ocean currents
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Hydroelectric Dams
• Convert a river’s hydraulic energy into electrical
power
• Quebec derives almost all of its electricity from
hydro dams
• Water flowing through the dam’s turbine creates
electricity which is then distributed to cities and
factories.
• Produce little greenhouse gases, but cause
large areas of flooding upstream of the dam
• This flooding, in turn, can release toxic mercury
into the environment
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James Bay Hydroelectric Dam
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Waves and Ocean Currents
• Buoys that rise and fall with the waves can
be attached to turbines to create electrical
energy
• Underwater turbines can harness ocean
current energy much the same way a
windmill operates
• Most of these ideas are still in the
prototype stage
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2.5 Pollution and Degradation of
Water Resources
• Chemical pollution metals, mercury,
PCB’s, mine drainage
• Thermal pollution heat discharge from
factories can decrease oxygen content
and lead to fish kills
• Oil spills 6 million tonnes per year
• Plastics north Pacific Gyre an ocean
“garbage dump”
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Fish Kill
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Oil Spills
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North Pacific Trash Gyre
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Eutrophication
• Farming activities add excess fertilizers to rivers
and lakes (mostly phosphorus and nitrogen).
• These excess fertilizers can stimulate algae
growth.
• Excess algae growth can then lead to algae
blooms, toxins being produced, reduced oxygen
levels, fish kills and green scum forming on
lakes.
• This whole process is called eutrophication.
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Eutrophication
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Eutrophication
experiment
conducted by
the University of
Manitoba.
Can you guess
to which side of
the lake fertilizer
was added?
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Hydrosphere Review
• Answer questions 20 to 36 on pages 215216.
• Use your notes and refer to pages 200 to
213 in Observatory to guide you in your
answers.
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