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Questions and Answers
What percentage of the Earth's surface would be covered by ocean water if the surface were completely smooth?
What percentage of the Earth's surface would be covered by ocean water if the surface were completely smooth?
What is the average elevation of the continents above sea level?
What is the average elevation of the continents above sea level?
What is the primary source of dissolved components in seawater?
What is the primary source of dissolved components in seawater?
What is the approximate percentage of dissolved substances in seawater?
What is the approximate percentage of dissolved substances in seawater?
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Which of the following is NOT one of the most abundant elements in seawater?
Which of the following is NOT one of the most abundant elements in seawater?
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How do oceanographers typically express salinity?
How do oceanographers typically express salinity?
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What is the approximate amount of dissolved components transported to the oceans by streams annually?
What is the approximate amount of dissolved components transported to the oceans by streams annually?
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What is the Southern Ocean located below?
What is the Southern Ocean located below?
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What is the primary factor that affects the shape of the ocean surface?
What is the primary factor that affects the shape of the ocean surface?
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What is the name given to the edges of diverging plates that are not associated with plate boundaries?
What is the name given to the edges of diverging plates that are not associated with plate boundaries?
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What is the average width of a continental shelf?
What is the average width of a continental shelf?
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What is the purpose of combining satellite altimeter data with sonar measurements?
What is the purpose of combining satellite altimeter data with sonar measurements?
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What type of margins are associated with an abundance of earthquake and volcanic activity?
What type of margins are associated with an abundance of earthquake and volcanic activity?
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What is the name given to the steep structure that marks the boundary between continental and oceanic crust?
What is the name given to the steep structure that marks the boundary between continental and oceanic crust?
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What is the significance of the continental shelf in terms of economic deposits?
What is the significance of the continental shelf in terms of economic deposits?
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What is the average inclination of a continental slope?
What is the average inclination of a continental slope?
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What is the name given to the submerged out edge of a continent?
What is the name given to the submerged out edge of a continent?
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What is the result of a 2,000 meter underwater volcano on the ocean surface above it?
What is the result of a 2,000 meter underwater volcano on the ocean surface above it?
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What is the average slope of the continental rise?
What is the average slope of the continental rise?
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What is characteristic of turbidites?
What is characteristic of turbidites?
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What is the term for the chaotic accumulation of sediment and oceanic material at an active continental margin?
What is the term for the chaotic accumulation of sediment and oceanic material at an active continental margin?
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What is the approximate width of the continental shelf at an active continental margin?
What is the approximate width of the continental shelf at an active continental margin?
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What is the primary location of deep-ocean trenches?
What is the primary location of deep-ocean trenches?
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What is the term for the deepest parts of the ocean?
What is the term for the deepest parts of the ocean?
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What is the relationship between deep-ocean trenches and volcanic activity?
What is the relationship between deep-ocean trenches and volcanic activity?
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What is the term for the movement of dense, sediment-laden water down a slope?
What is the term for the movement of dense, sediment-laden water down a slope?
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What is the term for the gradual incline that grades from the steep continental slope?
What is the term for the gradual incline that grades from the steep continental slope?
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What is the term for the landward wall of the trench at an active continental margin?
What is the term for the landward wall of the trench at an active continental margin?
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What percentage of the Earth's surface is covered by the oceans and marginal seas?
What percentage of the Earth's surface is covered by the oceans and marginal seas?
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Which hemisphere is referred to as the land hemisphere?
Which hemisphere is referred to as the land hemisphere?
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What is the average depth of the Pacific Ocean?
What is the average depth of the Pacific Ocean?
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Which ocean is growing larger?
Which ocean is growing larger?
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What is the primary focus of oceanography?
What is the primary focus of oceanography?
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What percentage of the surface is water in the Southern Hemisphere?
What percentage of the surface is water in the Southern Hemisphere?
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What is the estimated number of seamounts that exist?
What is the estimated number of seamounts that exist?
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What is the process that occurs when rocks rise and experience a reduction in pressure, causing them to melt without additional energy input?
What is the process that occurs when rocks rise and experience a reduction in pressure, causing them to melt without additional energy input?
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What is the term used to describe seamounts with flattened tops that were once islands but have been lowered due to weathering and erosion?
What is the term used to describe seamounts with flattened tops that were once islands but have been lowered due to weathering and erosion?
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What is the longest continuous geographic feature on Earth?
What is the longest continuous geographic feature on Earth?
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What is the approximate percentage of the Earth's solid surface covered by the Mid-Ocean Ridge?
What is the approximate percentage of the Earth's solid surface covered by the Mid-Ocean Ridge?
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What is the primary location where new oceanic crust is being generated?
What is the primary location where new oceanic crust is being generated?
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What is the term used to describe the process of seafloor spreading, where magma rises to the surface and solidifies?
What is the term used to describe the process of seafloor spreading, where magma rises to the surface and solidifies?
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What is the approximate time it takes for newly formed oceanic crust to completely cool and contract?
What is the approximate time it takes for newly formed oceanic crust to completely cool and contract?
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What is the classification of marine sediments that are derived from organisms?
What is the classification of marine sediments that are derived from organisms?
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What is a characteristic of abyssal plains?
What is a characteristic of abyssal plains?
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What is the term used to describe the process of sediment accumulation on the ocean floor?
What is the term used to describe the process of sediment accumulation on the ocean floor?
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What is the primary source of sediment in abyssal plains?
What is the primary source of sediment in abyssal plains?
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What feature occasionally interrupts the flatness of an abyssal plain?
What feature occasionally interrupts the flatness of an abyssal plain?
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Why are abyssal plains most extensive in the Atlantic Ocean?
Why are abyssal plains most extensive in the Atlantic Ocean?
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What is the process by which sediment is deposited on top of an irregular oceanic floor?
What is the process by which sediment is deposited on top of an irregular oceanic floor?
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What percentage of the ocean water is in the deep zone?
What percentage of the ocean water is in the deep zone?
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What is the primary purpose of bathymetry?
What is the primary purpose of bathymetry?
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What is the name of the deepest point in the ocean?
What is the name of the deepest point in the ocean?
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How do sonar devices measure ocean depth?
How do sonar devices measure ocean depth?
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What is the limitation of multibeam sonar?
What is the limitation of multibeam sonar?
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What is the purpose of seismic reflection profiles?
What is the purpose of seismic reflection profiles?
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What is the role of sidescan sonar?
What is the role of sidescan sonar?
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What is the limitation of satellite/radar altimetry?
What is the limitation of satellite/radar altimetry?
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What is the percentage of the ocean seafloor that has been mapped?
What is the percentage of the ocean seafloor that has been mapped?
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What is the characteristic of the ocean floor in high latitudes?
What is the characteristic of the ocean floor in high latitudes?
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Why is the salinity of the oceans not increasing despite the continuous addition of elements by streams and volcanic eruptions?
Why is the salinity of the oceans not increasing despite the continuous addition of elements by streams and volcanic eruptions?
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What is the main factor that affects the surface water temperature in the open ocean?
What is the main factor that affects the surface water temperature in the open ocean?
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What is the term for the rapid change in temperature observed between 980 feet and 3,300 feet in low-latitude regions?
What is the term for the rapid change in temperature observed between 980 feet and 3,300 feet in low-latitude regions?
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What is the definition of density?
What is the definition of density?
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Which of the following factors has the greatest impact on the density of seawater?
Which of the following factors has the greatest impact on the density of seawater?
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What is the term for the layer of density change with increasing depth in low-latitude regions?
What is the term for the layer of density change with increasing depth in low-latitude regions?
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Why does the salinity of the Persian Gulf and Red Sea exceed 42‰?
Why does the salinity of the Persian Gulf and Red Sea exceed 42‰?
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What is the term for the process of water sinking or rising due to density differences?
What is the term for the process of water sinking or rising due to density differences?
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What is the term for the layer in the ocean where the temperature and density remain constant with increasing depth?
What is the term for the layer in the ocean where the temperature and density remain constant with increasing depth?
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What is the main reason for the variation in salinity of different bodies of water?
What is the main reason for the variation in salinity of different bodies of water?
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What is the primary mode of transportation for larger terrigenous sediment particles?
What is the primary mode of transportation for larger terrigenous sediment particles?
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What is the approximate time required for a 1 centimeter abyssal clay deposit to form?
What is the approximate time required for a 1 centimeter abyssal clay deposit to form?
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What type of biogenous sediment is formed from the remains of organisms that inhabit warm waters?
What type of biogenous sediment is formed from the remains of organisms that inhabit warm waters?
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What is the term for the rounded, hard lumps of manganese, iron, cobalt, and other metals that precipitate in concentric layers around a central object?
What is the term for the rounded, hard lumps of manganese, iron, cobalt, and other metals that precipitate in concentric layers around a central object?
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What is the term for the sediments that form as a result of evaporation of seawater in restricted ocean basins?
What is the term for the sediments that form as a result of evaporation of seawater in restricted ocean basins?
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What type of sediment is formed from the impact of meteorites on Earth or other planets?
What type of sediment is formed from the impact of meteorites on Earth or other planets?
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What is the primary characteristic of deep-ocean sediments?
What is the primary characteristic of deep-ocean sediments?
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What is the primary factor that determines the type of biogenous sediment that forms?
What is the primary factor that determines the type of biogenous sediment that forms?
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Study Notes
The Vast World Ocean
- The Earth is often referred to as the water planet or the blue planet, with approximately 71% of its surface covered by the oceans and marginal seas.
- The distribution of water and land is not uniform between the Northern and Southern Hemispheres:
- Northern Hemisphere: 61% water, 39% land (termed the land hemisphere)
- Southern Hemisphere: 81% water, 19% land (termed the water hemisphere)
- Oceanography is the interdisciplinary science that studies all aspects of the world ocean.
Divisions of the World Ocean
- The world ocean can be divided into four main ocean basins:
- Pacific Ocean: largest ocean, covering over 50% of the Earth's ocean surface, and the deepest ocean (average depth of 12,927 feet)
- Atlantic Ocean: about half the size of the Pacific Ocean, with a slightly smaller depth
- Indian Ocean: slightly smaller than the Atlantic Ocean, with a similar depth
- Arctic Ocean: about 7% the size of the Pacific Ocean, with a depth of about 1/4 of the other oceans
- Oceanographers also recognize a fifth ocean basin: the Southern Ocean, located below 50° S latitude, surrounding the continent of Antarctica.
Composition of Seawater
- Seawater is not just saltwater; it contains a variety of other salts, metals, and gases dissolved in it.
- Every naturally occurring element is found in seawater, making it unsuitable for drinking or irrigation.
- The dissolved substances in seawater make up about 3.5% of its weight.
- Salinity, the total amount of solid, inorganic material dissolved in seawater, is typically expressed in parts per thousand (‰).
- The most abundant elements in seawater are Cl-, Na+, SO42-, Mg2+, Ca2+, and K+, which make up more than 99% of the dissolved substances.
Sources of Dissolved Components
- There are two sources of dissolved components in seawater:
- Chemical weathering of rocks on the continents, which are transported to the oceans by streams
- Earth's interior, through volcanic eruptions and other processes
Variations in Temperature and Density with Depth
- Surface water temperature varies depending on the amount of solar radiation received, with colder temperatures near the poles and warmer temperatures near the equator.
- Water temperature and density change with depth:
- In low-latitude regions, water temperature decreases rapidly with depth, resulting in a thermocline and a pycnocline
- In high-latitude regions, water temperature and density are relatively constant with depth
- The ocean is layered by density differences, with three main layers:
- Surface mixed zone: nearly uniform temperatures, varying in thickness and temperature due to latitude and season
- Transition zone: temperature falls with increasing depth, including a prominent thermocline and pycnocline
- Deep zone: constant water temperature, just above freezing
An Emerging Picture of the Ocean Floor
- The ocean floor is not smooth, with topography more variable than the landscape of the continents.
- The science of measuring ocean depths and charting the shape of the ocean floor is called bathymetry.
- Three methodologies are used to map the ocean floor:
- Sonar (Sound Navigation and Ranging)
- Seismic Reflection Profiles
- Satellite/Radar Altimeters
Continental Margins
- Continental margins are the submerged outer edges of a continent.
- There are two types of continental margins:
- Passive continental margins: not associated with plate boundaries, with relatively little earthquake or volcanic activity
- Active continental margins: near the edges of converging plates, with abundant earthquake and volcanic activity
- Features of passive continental margins include:
- Continental shelf
- Continental slope
- Continental rise
- Submarine canyons and turbidity currents
Deep-Ocean Basins
- Located between the continental margin and oceanic ridge system, deep-ocean basins cover about 30% of the Earth's surface.
- Features of deep-ocean basins include:
- Deep-ocean trenches
- Abyssal plains
- Seamounts, guyots, and oceanic plateaus### Seamounts, Guyots, and Oceanic Plateaus
- Seamounts are conical volcanic projections that rise more than 0.6 miles above the seafloor, with over 1 million estimated to exist, mostly in the Pacific Ocean.
- Some seamounts grow to become islands, while others form linear chains or near oceanic ridges.
- Guyots, also known as tablemounts, are seamounts with flattened tops, formed when islands sink due to weathering and erosion.
- Oceanic plateaus are flood basalts formed on the ocean seafloor from mantle plumes, composed of basaltic and ultramafic rocks that can exceed 30 km in thickness.
The Oceanic Ridge
- The oceanic ridge is a divergent plate boundary where the ocean seafloor is elevated, characterized by extensive faulting, earthquakes, high heat flow, and volcanic structures.
- It is the longest continuous geographic feature on Earth, covering over 20% of the planet's solid surface and extending over 43,000 miles.
- The crests of the ridge can rise 2 to 3 km above the ocean seafloor, comparable to some mountain ranges on continents.
Seafloor Spreading
- Harry Hess proposed seafloor spreading in the early 1960s, where magma rises to the ridge axis, replacing oceanic material that has shifted horizontally.
- As rocks rise, they experience decompression melting, resulting in new oceanic crust being generated.
- New material is added equally to each side of the ridge, with the process taking approximately 80 million years for the newly formed material to cool and contract.
Seafloor Sediments
- Most of the ocean floor is covered with sediments of varying thicknesses, with marine sediments classified into four categories according to their origin: terrigenous, biogenous, hydrogenous, and cosmogenous.
- Terrigenous sediments consist of mineral grains weathered from continental rocks and transported to the ocean by streams or winds.
- Biogenous sediments consist of shells and skeletons of marine animals and algae, including calcareous ooze and siliceous ooze.
- Hydrogenous sediments consist of minerals that precipitate directly from seawater through chemical reactions, including manganese nodules, calcium carbonates, metal sulfides, and evaporites.
- Cosmogenous sediments, not discussed in the text, include tektites and meteorites.
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Description
Quiz about the Earth's oceans, their distribution and coverage on the planet, and the difference in water and land distribution between the Northern and Southern Hemispheres.
