Focus Question 9.1 How does the area of Earth’s surface covered by oceans compare with the area covered by continents? 2

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

The Vast World Ocean

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

The Vast World Ocean

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 7

Focus Question 9.2 What are the two primary sources for the elements that comprise the dissolved components in seawater? 8

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

Dissolved Components in Seawater

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

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

Composition of Seawater

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 14

Focus Question 9.3 What two factors influence seawater density? Which one has the greater influence on surface seawater density? 15

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)

Variations in Temperature and Density with Depth

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)

Variations in Temperature and Density with Depth

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

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 21

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. 22

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

An Emerging Picture of the Ocean Floor

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

An Emerging Picture of the Ocean Floor

An Emerging Picture of the Ocean Floor

An Emerging Picture of the Ocean Floor

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

An Emerging Picture of the Ocean Floor

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. 31

Focus Question 9.5 Describe the differences between active and passive continental margins. Where is each type found? 32

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

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

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

Continental Margins Submarine canyons Turbidity currents 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

Continental Margins

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

Continental Margins

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

Continental Margins

Continental Margins

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 43

Focus Question 9.6 Explain how deep-ocean trenches are related to plate boundaries. 44

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

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

Features of Deep-Ocean Basins

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. 48

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. 49

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

The Oceanic Ridge

The Oceanic Ridge

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

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

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 55

Focus Question 9.8 List and describe the three basic types of seafloor sediments. 56

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 deep- ocean floor

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

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

Seafloor Sediments

Seafloor Sediments Hydrogenous sediment Minerals that precipitate directly from seawater Most common types include: Manganese nodules Calcium carbonates Metal sulfides Evaporites

Seafloor Sediments

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)

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

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 65