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Chapter 15 Grade 8 Earth Science
Earth’s Oceans Chapter 15 Grade 8 Earth Science
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Data Collection and Analysis (15.1)
At the surface Sonar (sound navigation and ranging) Help scientists learn about topography of sea floor Uses sound waves Calculate depth by measuring how long the sound takes to hit the bottom and come back Formula (time)(1500m/s)/2 1500m/s is constant velocity that sound travels in water
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Data Collection and Analysis
At the Surface Side-scan sonar Directs sound waves at ocean floor at an angle Helps get a picture of underwater hills TOPEX/Poseidon Use floats that contain sensors Measures temperature, salinity, concentration of gases and nutrients in surface water
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Data Collection and Analysis
In the Deep Sea Submersibles Underwater vessels that can carry people and instruments into the deepest water Used to observe animals Used to observe geologic features Hydrothermal vents Used to collect sediments from the seafloor for further study
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Data Collection and Analysis
Computers Collects and analyzes data from Satellites Float sensors Produces models that scientists can study Simulate Earth’s changing climate Simulate tides, tsunamis Simulate dispersion of coastal pollution
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Origin of Oceans Hypothesis
Water originated from either a remote source or a local source, or both Comets could have contributed to water Tail of ice Meteorite Composed similar to comet Bombardment of earth over time could have contributed to water accumulation
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Origin of Oceans Volcanism
A mechanism that could have allowed existing water from within the earth to rise Eruptions emit gases Water vapor Carbon dioxide Young earth was hotter with far more eruptions than today Could have released huge amounts of water vapor which condensed to oceans
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Distribution of Earth’s Water
Oceans contain 97% of Earth’s water Frozen ice caps contain 3% Over geologic time the percentage of ice has varied From near 0% to 10%
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The Blue Planet 71% of Earth’s surface covered with water All oceans-
Makes Earth look blue Average depth of oceans: 3800 m Landmasses like islands Most landmasses in Northern hemisphere Water only covers 61% of surface Southern Hemisphere 81% surface covered All oceans- One vast, interconnected body of water
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Sea Level Global Sea Level Level of the oceans’ surface
Has risen and fallen hundreds of meters Response to melting glaciers Tectonic forces pushing continents up or down Rising or sinking seafloor
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Major Oceans Three major oceans
Atlantic water above arctic circle is known as Arctic Ocean Pacific Largest, contains half Earth’s seawater Indian Ocean surround Antarctica is the Southern Ocean Polar Oceans (Arctic and Southern) Covered with snow pack year round No warm summers to thaw them
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Ocean and Atmospheric Interaction
Provide moisture and heat to atmosphere Influence large-scale circulation patterns Warm ocean water aide formations of Hurricanes Tropical cyclones Influences position of jet stream Plays a role in El Nino Huge supply of carbon dioxide Oceans keeps amount of CO2 in check
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Seawater Chapter 15.2
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Seawater Chemical Properties of Seawater Contains
Dissolved gases Oxygen Carbon dioxide Dissolved nutrients Nitrates Phosphates Chemical properties vary with location and depth
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Chemical Properties of Seawater
Salinity The amount of dissolved salts in seawater Expressed as grams of salt per kilogram of water Parts per thousand (ppt) Total salt content of water averages 35 ppt Most abundant salt is sodium chloride Other salts Chlorides Magnesium Potassium Calcium
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Variations in Salinity
Actual salinity vary form place to place Subtropical regions More evaporation than precipitation Can be as high as 37 ppt Equatorial regions Abundant precipitation Salinity lower Polar regions Seawater diluted by melting ice Can be as low as 32 or 33 ppt
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Variations in Salinity
Estuaries Large rivers empty into the oceans Fresh water dilutes seawater Salinity low
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Sources of Sea Salt Geologic evidence indicate salinity of oceans similar to ancient oceans Sources Sulfur dioxide and chlorine Gases released from volcanoes Sodium and calcium From the weathering of crustal rocks
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Removal of Sea Salts Salinity doesn’t constantly increase because sea salts are removed Evaporation leave solid salts behind Organisms use this salt for shells, bones and teeth Become sediments on the sea floor
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Physical Properties of Seawater
Density Maximum density of freshwater:1.0 g/cm^2 Salt ions add to mass of seawater Increases density of seawater Cold water more dense than warm water Seawater density ranges 1.02 g/cm^2 to 1.03 g/cm^2
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Physical Properties of Seawater
Freezing point Variations of salinity affect freezing point Lower than freshwater Freshwater freezes 0 degrees C Seawater freezes -2 degrees C
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Absorption of Light Intensity of light decreases with depth
Water absorbs light Light penetrates upper 100 m Many organisms below 100 m are blind
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Temperature Profiles Plot changing water temperatures against depth
Vary depending on location Three layers Surface area 100 m thick Relatively warm Transitional layer Thermocline Characterized by rapidly decreasing temperatures Bottom layer Cold and dark with temperatures near freezing
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Water Masses Deepwater Masses Cold water comes from polar oceans
Surface water under ice of polar oceans cools Cold water is more dense Dense water sinks Three water masses Antarctic Bottom Water North Atlantic Deep Water Antarctic Intermediate Water
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Water Masses Intermediate Water Masses
Form in relatively salty water near Antarctica cools and sinks Water is slightly warmer and less dense Atlantic contains all three major deepwater masses Pacific and Indian oceans contain the two Antarctic deepwater masses
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Ocean Movements Chapter 15.3
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Waves Waves: rhythmic movement that carries energy through space or matter Crest: the highest point of a wave Trough: the lowest point of a wave Wave length the distance from crest to crest
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Waves Wavelength and speed increase when energy is added
Only energy moves forward Water moves in circles
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Wave Height Three factors Fetch Wind duration Wind speed
Expanse of water that the wind blows across Wind duration How long the wind blows Wind speed How fast the wind blows
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Breaking Waves Waves approaches shallow water
Water depth becomes less than half their wavelength Causes changes in movement of waves Waves slow down and catch up with the slower wave crests ahead Crest to crest wavelength decreases Crests collapse forward causing breakers Breakers: collapsing waves
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Tides The periodic rice and fall of sea level Tidal range Tide cycle
High tide: sea level rises Low tide: sea level falls Tidal range Difference in height of high and low tide Tide cycle Takes 24 hours and 50 minutes
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Moon Influence on Tides
Gravitational attraction among Earth, Moon and Sun Earth and Moon orbit a common center of gravity Unbalance forces of moon and Earth cause tidal bulges on opposite sides of Earth
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Sun’s Influence on Tides
Earth’s orbital motion affects tides Lunar tides twice as large as solar tides Moon is closer Depending on the lunar cycle, solar tides can either make tides bigger or smaller
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Tides Spring Tide Neap Tides
During full moon or new moon Earth, the sun and the moon are aligned causing higher tides Have a greater tidal range during winter in Northern Hemisphere, and summer in Southern Hemisphere Neap Tides First or third quarter moon sun and moon are at right angles to Earth Solar tides diminish lunar tides
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Currents Surface currents Occur in the top 100 to 200 m
Daily velocity: 100 km Follow predictable patterns Driven by wind systems Can also be affected by land masses (continents) Affected by Coriolis Effect
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Gyres Land masses deflect currents Five major gyres
Causes them to move in circular patterns Five major gyres North Pacific North Atlantic South Pacific South Atlantic Indian Ocean
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Gyres Northern Hemisphere Southern Hemisphere Around equator
Circulate clockwise Southern Hemisphere Circulate counter clockwise Around equator Move toward west and deflect toward the poles
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Upwelling Water moving vertically Originate in deeper waters
Below the thermocline Usually cold
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Density Currents Caused by the differences of the temperature and salinity of water Denser water sinks After water cools it moves away from the poles Circulate between major ocean basins Less dense water rises
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