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Chapter 9 Lecture Outline Foundations of Earth Science Seventh Edition Oceans: The Last Frontier Natalie Bursztyn Utah State University © 2014 Pearson Education, Inc. Focus Question 9.1 • How does the area of Earth’s surface covered by oceans compare with the area covered by continents? © 2014 Pearson Education, Inc. The Vast World Ocean • Earth is referred to as the blue planet – 71% of Earth’s surface is oceans and marginal seas – Continents and islands comprise the remaining 29% • The Northern Hemisphere is the land hemisphere • The Southern Hemisphere is the water hemisphere © 2014 Pearson Education, Inc. The Vast World Ocean © 2014 Pearson Education, Inc. The Vast World Ocean • Four main ocean basins 1. Pacific Ocean • The largest with the greatest depth 2. Atlantic Ocean • About half the size of Pacific and not as deep 3. Indian Ocean • Slightly smaller than Atlantic, largely in Southern Hemisphere 4. Arctic Ocean • About 7% the size of the Pacific © 2014 Pearson Education, Inc. The Vast World Ocean © 2014 Pearson Education, Inc. Focus Question 9.1 • How does the area of Earth’s surface covered by oceans compare with the area covered by continents? – 71% covered by oceans; 29% by land – Most land in northern hemisphere © 2014 Pearson Education, Inc. Focus Question 9.2 • What are the two primary sources for the elements that comprise the dissolved components in seawater? © 2014 Pearson Education, Inc. Composition of Seawater • Salinity – The total amount of solid material dissolved in water • Typically expressed as a percent • Dissolved substances in seawater are in such small quantities that expressed in parts per thousand • Most of the salt in seawater is sodium chloride © 2014 Pearson Education, Inc. Dissolved Components in Seawater © 2014 Pearson Education, Inc. Composition of Seawater • Sources of sea salts – Chemical weathering of continental rocks – Earth’s interior through volcanic eruptions • Process called outgassing • Composition of seawater has been relatively stable for millions of years – Material removed as rapidly as added © 2014 Pearson Education, Inc. Composition of Seawater • Processes affecting seawater salinity – Changes in water content of the solution • Addition of fresh water – Precipitation – Runoff – Icebergs and sea-ice melting • Removal of fresh water – Evaporation – Formation of sea ice – Latitude and seasons © 2014 Pearson Education, Inc. Composition of Seawater © 2014 Pearson Education, Inc. Focus Question 9.2 • What are the two primary sources for the elements that comprise the dissolved components in seawater? – Chemical weathering of continental rocks – Earth’s interior through volcanic eruptions © 2014 Pearson Education, Inc. Focus Question 9.3 • What two factors influence seawater density? Which one has the greater influence on surface seawater density? © 2014 Pearson Education, Inc. Variations in Temperature and Density with Depth • Temperature variations – Thermocline • Rapid change of temperature with depth • Thermo = heat • Cline = slope • Creates a vertical barrier in ocean column • Not present at high latitudes (isothermal) © 2014 Pearson Education, Inc. Variations in Temperature and Density with Depth © 2014 Pearson Education, Inc. Variations in Temperature and Density with Depth • Density variations – Influenced by salinity • Increased salinity = increased density – Influenced by temperature • Increased temperature = decreased density • Greater variations in temperature result in a greater impact of this factor on density – Influenced by depth • Increased depth = increased density • Pycnocline = rapid change of density with depth • Not present at high latitudes (isopycnal) © 2014 Pearson Education, Inc. Variations in Temperature and Density with Depth © 2014 Pearson Education, Inc. Variations in Temperature and Density with Depth • Layered ocean – Layered according to density – 3-layer structure • Shallow surface mixed zone • Transition zone • Deep zone – Does not exist in high latitudes © 2014 Pearson Education, Inc. Focus Question 9.3 • What two factors influence seawater density? Which one has the greater influence on surface seawater density? – Salinity and temperature – Temperature has the greater influence © 2014 Pearson Education, Inc. Focus Question 9.4 • Describe how satellites orbiting Earth can determine features on the seafloor without being able to directly observe them beneath several kilometers of seawater. © 2014 Pearson Education, Inc. An Emerging Picture of the Ocean Floor • Bathymetry – Mapping ocean depths and the shape, or topography, of the ocean floor • Echo sounder (sonar) – Invented in the 1920s – Primary instrument for measuring depth – Reflects sound from ocean floor © 2014 Pearson Education, Inc. An Emerging Picture of the Ocean Floor © 2014 Pearson Education, Inc. An Emerging Picture of the Ocean Floor • Multibeam sonar – Array of sound sources and listening devices – Obtains a profile of a narrow strip of seafloor • Satellite altimeter – Satellites equipped with radar altimeters – Measures variations of the sea surface from space © 2014 Pearson Education, Inc. An Emerging Picture of the Ocean Floor © 2014 Pearson Education, Inc. An Emerging Picture of the Ocean Floor © 2014 Pearson Education, Inc. An Emerging Picture of the Ocean Floor © 2014 Pearson Education, Inc. An Emerging Picture of the Ocean Floor • Provinces of the Ocean Floor – Three major topographic units 1. Continental margins • Passive • Active 2. Ocean basin floor • Seamount • Abyssal plain 3. Mid-ocean ridge • Rift valley © 2014 Pearson Education, Inc. An Emerging Picture of the Ocean Floor © 2014 Pearson Education, Inc. Focus Question 9.4 • Describe how satellites orbiting Earth can determine features on the seafloor without being able to directly observe them beneath several kilometers of seawater. – Satellites measure differences across the ocean surface. These differences are due to water displacement caused by variations of the ocean floor. © 2014 Pearson Education, Inc. Focus Question 9.5 • Describe the differences between active and passive continental margins. Where is each type found? © 2014 Pearson Education, Inc. Continental Margins • Passive continental margins – Found along most coastal areas that surround the Atlantic Ocean – Not associated with plate boundaries • Experience little volcanism • Few earthquakes © 2014 Pearson Education, Inc. Continental Margins • Passive continental margin features – Continental shelf • Flooded extension of the continent • Varies greatly in width • Gently sloping • Contains oil and important mineral deposits • Some areas mantled by extensive glacial deposits • Most consist of thick accumulations of shallow-water sediments © 2014 Pearson Education, Inc. Continental Margins • Passive continental margin features – Continental slope • Marks the seaward edge of the continental shelf • Relatively steep structure • Boundary between continental crust and oceanic crust © 2014 Pearson Education, Inc. Continental Margins • Passive continental margin features – Submarine canyons • Deep, steep-sided valleys cut into continental slope • Some are seaward extensions of river valleys • Most appear to have been eroded by turbidity currents – Turbidity currents • Downslope movements of dense, sediment-laden water • Deposits are turbidites © 2014 Pearson Education, Inc. Continental Margins © 2014 Pearson Education, Inc. Continental Margins • Passive continental margin features – Continental rise • Found in regions where trenches are absent • Continental slope merges into a more gradual incline • At base of the continental slope, turbidity currents deposit deep-sea fans © 2014 Pearson Education, Inc. Continental Margins © 2014 Pearson Education, Inc. Continental Margins • Active continental margins – Continental slope descends abruptly into a deep-ocean trench – Located primarily around the Pacific Ocean – Accumulations of deformed sediment and ocean crust form accretionary wedges – Some subduction zones have little or no accumulation of sediments © 2014 Pearson Education, Inc. Continental Margins © 2014 Pearson Education, Inc. Continental Margins © 2014 Pearson Education, Inc. Focus Question 9.5 • Describe the differences between active and passive continental margins. Where is each type found? – Passive margins mark the boundary between continental and oceanic crust on a single tectonic plate – Passive margins accumulate sediment – Active margins mark the boundary between tectonic plates – Active margins are found along all subduction zones © 2014 Pearson Education, Inc. Focus Question 9.6 • Explain how deep-ocean trenches are related to plate boundaries. © 2014 Pearson Education, Inc. Features of Deep-Ocean Basins • Deep-ocean trenches – – – – – Long, relatively narrow features Deepest parts of ocean Most are located in the Pacific Ocean Located at subduction zones Associated with volcanic activity • Volcanic island arcs • Continental volcanic arcs © 2014 Pearson Education, Inc. Features of Deep-Ocean Basins • Abyssal plains – Likely the most level places on Earth – Sites of thick accumulations of sediment – Found in all oceans • Seamounts and guyots – Isolated volcanic peaks – Many form near oceanic ridges – May emerge as islands – May sink and form flat-topped seamounts called guyots or tablemounts © 2014 Pearson Education, Inc. Features of Deep-Ocean Basins © 2014 Pearson Education, Inc. Focus Question 9.6 • Explain how deep-ocean trenches are related to plate boundaries. – Deep ocean trenches form at subduction zones, which are a form of convergent plate boundary. © 2014 Pearson Education, Inc. Focus Question 9.7 • Although oceanic ridges can be as tall as some mountains on the continents, list some ways that oceanic ridges are different. © 2014 Pearson Education, Inc. The Oceanic Ridge • Mid-ocean ridge – Interconnected ridge system is the longest topographic feature on Earth’s surface • Over 70,000 km (43,000 mi) in length • 23% of Earth’s surface • Winds through all major oceans – Along axis of some segments are deep downfaulted structures called rift valleys © 2014 Pearson Education, Inc. The Oceanic Ridge © 2014 Pearson Education, Inc. The Oceanic Ridge © 2014 Pearson Education, Inc. The Oceanic Ridge • Oceanic ridges are characterized by: – An elevated position – Extensive faulting – Numerous volcanic structures that have developed on newly formed crust • Consist of layer upon layer of faulted and uplifted basaltic rocks • Mid-Atlantic ridge has been studied more thoroughly than any other ridge system © 2014 Pearson Education, Inc. The Oceanic Ridge • Elevated position of ridge – Due to hot (less dense) newly formed crust – Cools, contracts and becomes denser as it moves away from mantle upwelling © 2014 Pearson Education, Inc. Focus Question 9.7 • Although oceanic ridges can be as tall as some mountains on the continents, list some ways that oceanic ridges are different. – Type of plate boundary – Type of volcanism (and composition of lava) – Type of tectonic stress and resulting features © 2014 Pearson Education, Inc. Focus Question 9.8 • List and describe the three basic types of seafloor sediments. © 2014 Pearson Education, Inc. Seafloor Sediments • Ocean floor is mantled with sediment • Sources – Turbidity currents – Sediment slowly settles to bottom from above • Thickness varies – Thickest in trenches: up to 10 km – Pacific Ocean: 600 m or less – Atlantic Ocean: 500 to 1000 m – Mud is most common sediment on deepocean floor © 2014 Pearson Education, Inc. Seafloor Sediments • Types of seafloor sediments – Terrigenous sediment • Material weathered from continental rocks • Virtually every part of the ocean receives it • Fine particles remain suspended for a long time • Oxidation often produces red and brown colored sediments © 2014 Pearson Education, Inc. Seafloor Sediments • Biogenous sediment – Shells and skeletons of marine organisms – Most common are calcareous oozes – Siliceous oozes composed of skeletons of diatoms and radiolarians – Phosphate rich materials derived from bones, teeth, and fish scales © 2014 Pearson Education, Inc. Seafloor Sediments © 2014 Pearson Education, Inc. Seafloor Sediments • Hydrogenous sediment – Minerals that precipitate directly from seawater – Most common types include: • Manganese nodules • Calcium carbonates • Metal sulfides • Evaporites © 2014 Pearson Education, Inc. Seafloor Sediments © 2014 Pearson Education, Inc. Seafloor Sediments • Distribution – Coarse terrigenous deposits dominate continental margin areas – Fine terrigenous material common in deeper areas of the ocean basin – Hydrogenous sediment comprises only a small portion of deposits in the ocean – Few places where very little sediment accumulates (mid-ocean ridges) © 2014 Pearson Education, Inc. Seafloor Sediments • A Storehouse of Climate Data – Organisms recording climate data become part of the sedimentary record – Records of temperature changes revealed in sediment cores from ocean floor © 2014 Pearson Education, Inc. Focus Question 9.8 • List and describe the three basic types of seafloor sediments. 1. Terrigenous — weathered from continental rocks 2. Hydrogenous — precipitated directly from seawater 3. Biogenous — produced by marine organisms © 2014 Pearson Education, Inc.