The HydrosphereObservatory 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 watershedSTESTAST

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• Wind driven ocean currents• Push the top 400m of water• eg: The Gulf Stream current• See map diagram on p. 204-205 of

Observatory

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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

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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”ESTSE

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.ESTES

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 215-

216.• Use your notes and refer to pages 200 to

213 in Observatory to guide you in your answers.

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